Immunology: Medical School Crash Course by AudioLearn

Introduction to Immunology Medical School Crash Course ™

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Table of Contents Preface............................................................................................................................................ 1 Chapter 1: Overview of the Human Immune Response............................................................ 3 Natural Barriers to Pathogens .................................................................................................... 3 Nonspecific Responses............................................................................................................... 4 Specific Responses ..................................................................................................................... 4 Overview of the Human Immune System .................................................................................. 4 The Barrier System .................................................................................................................... 5 Innate Immune System............................................................................................................... 6 Inflammation .............................................................................................................................. 6 Complement System .................................................................................................................. 7 Cellular Immunity ...................................................................................................................... 8 Adaptive Immune System ........................................................................................................ 10 Passive Immunity ..................................................................................................................... 11 Active Immunity ...................................................................................................................... 12 Key Takeaways ........................................................................................................................ 12 Quiz .......................................................................................................................................... 12 Chapter 2: Innate Immunity ...................................................................................................... 16 Innate Immune System Basics ................................................................................................. 16 Barrier Features ........................................................................................................................ 16 The Inflammatory Response .................................................................................................... 17 Phagocytosis............................................................................................................................. 21 Key Takeaways ........................................................................................................................ 22 Quiz .......................................................................................................................................... 23 Chapter 3: Antigens and Antibodies ......................................................................................... 26 Antigens ................................................................................................................................... 26 Antibodies ................................................................................................................................ 30 Key Takeaways ........................................................................................................................ 34 Quiz .......................................................................................................................................... 34 Chapter 4: Adaptive Immunity and the T Cell ........................................................................ 37 Cell-Mediated Immunity .......................................................................................................... 37 T Lymphocytes......................................................................................................................... 39

T Cell Development ................................................................................................................. 40 Activation of T Cells ................................................................................................................ 42 T Cell-Related Diseases ........................................................................................................... 43 Key Takeaways ........................................................................................................................ 44 Quiz .......................................................................................................................................... 44 Chapter 5: Adaptive Immunity and the B Cell ........................................................................ 48 Humoral Immunity ................................................................................................................... 48 Parts of the Humoral Immunity................................................................................................ 48 Mechanism of the Humoral Immune System........................................................................... 49 Complement System ................................................................................................................ 50 Antibodies ................................................................................................................................ 50 B Lymphocyte .......................................................................................................................... 51 B Lymphocyte Diseases ........................................................................................................... 54 Key Takeaways ........................................................................................................................ 54 Quiz .......................................................................................................................................... 55 Chapter 6: The Chemistry of the Immune Response —Cytokines and Complement Systems ......................................................................................................................................... 58 Cytokines.................................................................................................................................. 58 Cytokine Receptors .................................................................................................................. 59 Cytokines and Diseases ............................................................................................................ 60 Complement System ................................................................................................................ 61 Classical Complement Pathway ............................................................................................... 62 Alternative Complement Pathway ........................................................................................... 63 Lectin Complement Pathway ................................................................................................... 63 Complement-related Diseases .................................................................................................. 64 Key Takeaways ........................................................................................................................ 64 Quiz .......................................................................................................................................... 64 Chapter 7: Hypersensitivity Reactions and Allergies .............................................................. 68 Hypersensitivity ....................................................................................................................... 68 Type 1 Hypersensitivity Reactions .......................................................................................... 69 Type II Hypersensitivity Reactions .......................................................................................... 70 Type III Hypersensitivity Reactions ........................................................................................ 70 Type IV Hypersensitivity Reactions ........................................................................................ 71 Allergies ................................................................................................................................... 71 Key Takeaways ........................................................................................................................ 72 Quiz .......................................................................................................................................... 72

Chapter 8: Immunodeficiency States ........................................................................................ 76 HIV Disease ............................................................................................................................. 76 Stages of the Infection.............................................................................................................. 77 HIV Transmission .................................................................................................................... 78 Virology of HIV ....................................................................................................................... 79 Testing and Staging .................................................................................................................. 80 Prevention of AIDS .................................................................................................................. 81 Treatment of HIV ..................................................................................................................... 81 HIV Prognosis .......................................................................................................................... 82 Severe Combined Immunodeficiency Disease (SCID) ............................................................ 82 Key Takeaways ........................................................................................................................ 84 Quiz .......................................................................................................................................... 84 Chapter 9: Leukemias and Lymphomas................................................................................... 88 Leukemia .................................................................................................................................. 88 Explanation of Symptoms of Leukemia ................................................................................... 90 Causes of Leukemia ................................................................................................................. 90 Non-Hodgkin’s Lymphoma ..................................................................................................... 92 Hodgkin’s Lymphoma ............................................................................................................. 94 Key Takeaways ........................................................................................................................ 95 Quiz .......................................................................................................................................... 95 Chapter 10: Immunity and Transplantation ............................................................................ 99 Transplantation......................................................................................................................... 99 Types of Transplanted Grafts ................................................................................................... 99 The Immunology of Rejection ............................................................................................... 101 Rejection Mechanisms ........................................................................................................... 102 Stages of Rejection................................................................................................................. 104 Minimizing the Rejection Process ......................................................................................... 105 Immunosuppression in Transplantation ................................................................................. 105 Key Takeaways ...................................................................................................................... 106 Quiz ........................................................................................................................................ 106 Chapter 11: Autoimmune Diseases ......................................................................................... 109 Autoimmune Basics ............................................................................................................... 109 Types of Autoimmune Diseases............................................................................................. 111 Key Takeaways ...................................................................................................................... 112 Quiz ........................................................................................................................................ 113

Chapter 12: The Immune System and Infectious Diseases ................................................... 116 Infections ................................................................................................................................ 116 Disseminated Intravascular Coagulation................................................................................ 117 Sepsis...................................................................................................................................... 118 Key Takeaways ...................................................................................................................... 120 Quiz ........................................................................................................................................ 120 Summary .................................................................................................................................... 124 Course Questions and Answers ............................................................................................... 126

Preface The subject of this course is immunology and, specifically, human immunology or the responses that happen as part of the human immunological response to a variety of stimuli. The course is designed to cover the basics of what is involved in the human immune response, the cells and molecules involved, and how the immune system relates to certain exposures. Abnormalities of the human immune system are also intended to be covered as part of the course. The first chapter of the course will involve an overview of the human immune response and the various components of the bone marrow, lymph organs, and blood that are a part of this response. The immune response usually involves the response to a pathogen but can involve the response to cancer or to a diseased cell in the body. The second chapter of the course will mainly cover the innate immune system. This is the initial and nonspecific response the human host has to the environment, which involves cells and chemicals that don’t require antibodies or the sensitization of immune cells in which to function. The structure and function of the antigens and antibodies in the immune system will be the main topic of the third chapter of the course. These are molecules that interact with one another in a key part of the immune system. You will learn what constitutes an antigen and about the chemical makeup of antibodies. In the fourth chapter of the course, the adaptive immune system and the T cell will be the focus of discussion. The T lymphocyte is perhaps the main type of cell in the adaptive immune system, which requires the recognition of an antigen as being foreign and creating a cytotoxic response to the antigen. In the fifth chapter of the course, the adaptive immune system will continue to be discussed but the humoral component will be the focus of the discussion. The B cell will be discussed as it is the main cell responsible for making antibodies used by this component of the immune system. The sixth chapter of the course is intended to cover the chemicals involved in the immune system—namely, the cytokines and the complement system. Both molecular systems are in play as part of the humoral and adaptive immune system. Defects in the presence of these chemicals result in a defective immune system. The seventh chapter of the course will be a basic discussion of hypersensitivity reactions, of which allergies are a part. These are situations where the immune system is over-reactive and in which it is over-reactive to things that not everyone mounts an immune response to. 1

The eighth chapter in the course is designed to cover the topic of immunodeficiency states. The two main immunodeficiency states that will be covered include the human immunodeficiency virus disease or HIV disease and severe combined immunodeficiency disease, which is an inherited condition involving a poor immune system. The ninth chapter of the course is intended to be a discussion of various leukemias and lymphomas—both of which are cancers involving the immune system. Leukemias are divided into chronic leukemias and acute leukemias of the myeloid or lymphoid line, while there are a variety of lymphomas derived from either B cells or T cells. The tenth chapter of the course will involve a discussion of transplantation and the immune system. Transplantation involves providing organs or tissues to a person, usually from another person who is not a genetically-identical match to the recipient. The eleventh chapter of the course is intended to be a discussion of autoimmune diseases, which are diseases a person gets when they develop an immune response to something innate in their body that most people don’t mount an immune response to. The last and twelfth chapter of the course is all about the presence of serious infections and the immune response. Sometimes the immune system gets hyperreactive to a pathogen, starting a biochemical and cellular set of circumstances that overwhelm the organs of the body, leading to multiple end organ failure, disseminated intravascular coagulation, and possible death. This will conclude the course topics.

Chapter 1: Overview of the Human Immune Response The human immune system is how we protect ourselves from infection, cancer, and toxic substances. The immune system as a whole is an extremely complex system of cells and biological chemicals that work together to fight pathogens. This first chapter will cover the basics of the human immune response, including the natural barriers that are present, which prevent pathogens from ever invading the human body.

Natural Barriers to Pathogens The skin of the human is the main barrier to pathogens in the human body. It protects the body from most microorganisms unless there is some type of physical disruption. There are exceptions to pathogens the skin is able to protect us from, including human papillomavirus infections (as these can invade the skin) and certain parasitic infections that can invade the skin, such as infections from the Schistosoma species and Strongyloides species. The mucous membranes also provide a barrier to infection. Mucus membranes include those of the mouth, the rest of the respiratory tract, and the vaginal mucous membranes. Some mucous membranes are bathed in secretions that fight microbial organisms. There are secretions, for example, from the reproductive tract of both males and females, as well as eye secretions, that contain lysozyme, which acts to split the muramic acid linkage found in bacterial walls, providing an added antibacterial property to these tissues. IgG and IgA are secreted by other mucous membranes that interfere with the ability of microbes to attach to human tissue. The lining of the respiratory tract is an anti-microbial barrier. If organisms attach to the bronchial tree, there are cilia that move them away from the lungs. The act of coughing also clears microbes from the lungs. If bacteria do get into the alveoli there are macrophages and tissue histiocytes that get rid of the organisms. This works primarily for small numbers of organisms. Large numbers of organisms or things like the inhalation of tobacco smoke can overwhelm these defense mechanisms, leading to infection. The gastrointestinal tract acts like a barrier to infection. The acidic pH of the stomach acts to fight off bacteria and pancreatic enzymes, along with other intestinal secretions, fight off microorganisms. The peristaltic activity of the gastrointestinal tract removes microorganisms and if peristalsis is interrupted, infection can occur. Diseases like achlorhydria can predispose a person to infection. 3

The genitourinary tract also has barriers to infection. The length of the urethra brought in males prevents them from having urinary tract infections and the pH of the vagina is antibacterial. The medulla of the kidney is hypertonic, preventing bacteria from taking hold. The kidneys also produce a large amount of Tamm-Horsfall mucoprotein, which binds to pathogenic bacteria.

Nonspecific Responses There are cytokines, such as tumor necrosis factor-alpha, interleukin-1, and interferon-gamma, that are produced by macrophages and activated lymphocytes. These cause an acute phase response that is independent of the organism. The response involves things like fever and an elevation of the neutrophil count, which are nonspecific responses to infection. Endothelial cells secrete interleukin-8, which is attractive to neutrophils. All of this involves an inflammatory response directed by the immune system toward microbes that nonspecifically fights infection by increasing vascular permeability, increasing blood supply, and allowing immune cells to get into spaces that might be invaded by bacteria. The process of phagocytosis is completely nonspecific so that all types of organisms can be killed by the immune system.

Specific Responses After an infection, the human host can produce antibodies that specifically attack certain organisms. This process depends entirely on being exposed to the pathogen in the past. Antibodies are able to attract immune cells that can eradicate the specific organism. This involves the complement system. The complement system will be discussed in another chapter, but it basically involves destroying the cell walls of microorganisms that have invaded the body. Antibodies deposit opsonins on the surface of microorganisms, which allows for phagocytosis. This process of opsonization is particularly important in fighting certain bacteria, such as pneumococci and meningococci. Individuals who have certain deficiencies in the complement system will have more Infections. This is especially true of Neisseria infections.

Overview of the Human Immune System The human immune system involves many cells and processes that fight disease. To function correctly, the immune system must be able to detect organisms, have means to fight organism, and have means to get rid of organisms. Microorganisms can be viruses, bacteria, or parasites. The immune system must be able to tell the difference between healthy tissue and diseased tissue. There are two types of immune system functions in the body. These are the innate

immune system and the adaptive immune system. These will be discussed separately in other chapters. There is also humoral immunity and cell-mediated immunity. Humoral immunity involves the use of antibodies and chemical reactions that fight off infections the human host has already been exposed to. Innate immunity involves the killing of organisms in a nonspecific way. The human body relies on both systems to fight infection. Pathogens have ways to avoid detection by the immune system. They evolve and adapt to avoid being detected by the immune system. The ability to fight off microorganisms is not unique to humans; however, the human immune system is highly efficient and has evolved fight off many kinds of organisms. We have an immune system that recognizes prior Infections so we don’t get them again. In addition, we have vaccinations that protect against disease so that we never get the infection in the first place. Unfortunately, there are diseases of the immune system, such as autoimmune diseases, immunodeficiency diseases, neoplasms, and inflammatory diseases that can affect the human immune system. Some of these are genetic and some of them are acquired. Immunosuppressive medications are used in some cases to combat these diseases and to allow for things like transplantation and relief from overactive immune system problems. The human immune system is a type of layered defense system, involving barriers, immune cells, and biochemical immune reactions. The first layer involves barriers. If bacteria or other pathogens get through the barriers, the rest of the immune system is activated. The innate immune system uses phagocytosis to engulf bacteria or other pathogens without the need for antibodies. The humoral immune system uses antibodies and chemical reactions to quickly avoid infection. The basis behind the adaptive immune system involves recognizing previous infections by a pathogen and quickly mounting an immune response so that a fast response can be made against the organism, preventing an infection and improving the immune response. There is a form of immunological memory used by the adaptive immune system that lasts a lifetime of the human host. This allows for a stronger attack against an organism the host has encountered before.

The Barrier System Most higher organisms, as mentioned, use the barrier system as a first line of defense against pathogens. In plants, the waxy cuticle of leaves protects the plants against microorganisms. In insects, it is the exoskeleton that provides the barrier against microorganisms. In humans, the barrier system involves the skin, respiratory mucous membranes, genitourinary membranes,

flushing action of tears and urine, and the production of mucus. All of these things nonspecifically repel microorganisms or prevent them from taking hold. The human host has chemical barriers against infection. There are antimicrobial peptides, such as the beta-defensins, and enzymes, such as lysozyme and phospholipase A2, found in saliva, breast milk, in human tears, that act as antibacterial agents. The secretions made by the human vagina act as chemical barriers against infection, while male semen contains defensins as well as zinc that fight off pathogens. Stomach acid and proteases in the stomach are defense mechanisms against ingested pathogens. In the genitourinary system and in the gastrointestinal tract, there are bacterial flora that act as biological barriers prevent pathogenic bacteria from taking hold and causing infection. This involves a symbiotic relationship between the bacteria in the human host. Unfortunately, when we take antibiotics, we often kill off the symbiotic bacteria, compromising immunity. This is how infections like candidiasis can develop in the human host after taking antibiotics. There is evidence to suggest that taking probiotic bacterial products are effective in preventing many types of human infections.

Innate Immune System The innate immune system is found in all forms of life and involves no immunological memory. The response is entirely nonspecific and exposure to the pathogen leads to a maximal immune response, regardless of the number of organisms or pathogens the host is exposed to. Even though the response is nonspecific, it does depend on being able to tell the difference between self-molecules and non-self-molecules. This must be the case so that the nonspecific immune system doesn’t fight off itself. Even the nonspecific immune system recognizes receptors on cells belonging to the host so that host cells are protected. While barriers in the host are the first defense mechanism, the innate immune system can be considered the second line of defense. It becomes involved when the barrier is ineffective. They are pattern recognition receptors on host cells that are recognized by phagocytes whenever a pathogen is identified. A damaged or injured cell will send out a message that activates the innate immune system. This immune system is very fast but is not long-lasting. Nevertheless, it is the dominant system of defense against pathogens of most organisms.

Inflammation Inflammation is part of the innate immune system. Inflammation can be seen in the form of redness, localized heat, swelling, and pain that come when an infection has taken hold. Inflammation is caused by the production of cytokines and eicosanoids, which are molecules 6

released by damaged cells that activate the innate immune system. Eicosanoids include molecules like prostaglandins, which produce blood vessel dilatation and fever, both of which are found in infection. Cytokines include interleukins that help cells communicate with one another. Other cytokines include chemokines, which allow for chemotaxis, and interferons, which kill viruses. Figure 1 describes inflammation around a wound:

Figure 1 There are also cytotoxic factors and growth factors that are released as part of the innate immune system that attract immune molecules and immune cells that are effective in killing off pathogens in a nonspecific way and are involved in the removal of killed pathogen.

Complement System The complement system involves a cascade of biochemical molecules and attack the surfaces of foreign pathogens. There are more than twenty proteins that make up the complement system. The name “complement” is because they complement antibodies and immune cells in killing off pathogens. The complement system is not unique to human and can be found in lower order animals and plants as part of their defense system. 7

Figure 2 shows the complement pathway system:

Figure 2 In the human host, the complement system is activated only when there are antibodies against a pathogen and when the antibodies have bound to the pathogen as part of the humoral immune response. There are specific carbohydrates on the surfaces of pathogens that are recognized as foreign. Complement proteins binds to the carbohydrates, inducing a rapid killing response. The response is so rapid because antibodies allow for signal amplification, which is directly following the activation of the complement system. Most of the complement molecules are proteases. After the complement molecules bind to the pathogen, their proteolytic activity is activated, turning on the activity of still other complement molecules, so that the entire process involves a cascade of proteolytic and catalytic activity. This also results in the production of peptides near the pathogens that increase vascular permeability, attracting immune cells, allowing them to get through to the site of infection, and opsonizing the coating of the pathogen so that it is marked for immune destruction. Complement can also kill pathogens directly by causing a disruption of their cell membrane.

Cellular Immunity Certain leukocytes are part of the innate immune system as well as the humoral immune system. Innate leukocytes include macrophages, dendritic cells, innate lymphoid cells, basophils, natural killer cells, eosinophils, and neutrophils—all of which have phagocytic properties. They have the 8

innate ability to identify and eliminate pathogens by engulfing them entirely or piece-by-piece. Innate phagocytic cells also act in lymphoid organs of the body and are involved in activating the adaptive immune system. The main way that the innate immune cells kill off pathogens is through the phagocytic activity of these cells. Phagocytosis involves engulfing or eating pathogenic organisms or foreign particles. Phagocytes are always on patrol, looking for foreign substances to kill and eat. They can act independently or can be called upon to act by the complement system. The pathogenic particle becomes trapped inside a phagosome made by the phagocyte, which fuses with a lysosome inside the cell to form what is called a “phagolysosome”. This is how the foreign particle is digested. The digestive process can involve proteolysis or the release of free radicals inside the phagolysosome that damage the pathogen. Figure 3 indicates what phagocytosis looks like schematically:

Figure 3 Both macrophages and neutrophils are mobile and can travel to any place in the body to pursue and destroy pathogens. Neutrophils travel mainly through the bloodstream, while macrophages are found in the tissues. Neutrophils that participate in phagocytosis represent more than half of all circulating leukocytes. They go to the site of an infection by means of chemotaxis, which is a signaling mechanism that identifies areas of infection or invasion. Macrophages live within the tissues themselves and produce many types of chemicals, including proteases in the complement system, enzymes, and cytokines, which participate in the 9

identification of foreign substances and in the killing of foreign substances. They also get rid of cellular debris that result from apoptosis of old cells and destroy any antigen-presenting cells that are part of the adaptive immune system. Dendritic cells are also phagocytic cells that reside inside the body’s tissues. They are in direct contact with the external environment, meaning that they are primarily found in the intestinal tract, stomach, lungs, nose, and skin. They have spine-like projections similar to the dendritic cells in the central nervous system but are not nervous system cells. They link the humoral and innate immune system by presenting antigens to T cells in the adaptive immune system. Mast cells are also cells in the innate immune system that reside in both the mucous membranes and in the connective tissues of the body. They are closely linked to the anaphylactic response and to allergy. Mast cells can be basophils or eosinophils, which secrete certain chemical mediators involved in parasitic infections and in allergic reactions. Natural killer cells are specialized lymphocyte and are part of the innate immune system that does not directly attack microbes instead destroy tumor cells in cells infected with viruses. They are involved in a response called the “missing self” response. They identify the major histocompatibility complex on cells and if this complex is altered, the cells are attacked by natural killer cells, leaving normal cells alone, because they have self-recognizing receptors that prevent destruction of these cells.

Adaptive Immune System The adaptive immune system provides for a stronger immune response as well as mechanisms for immunological memory. Immunological memory means that a pathogen is remembered as having a particular antigen on its surface that is recognized by certain cells so that a similar infection cannot occur again. The adaptive immune system involves both antibodies and antigens. Antigen specificity of this immune system allows the host to kill specific pathogens that are identified as being dangerous. There are memory cells that carry the antibody response necessary for eliminating a pathogen that has infected the organism before. The main cells of the adaptive immune system are called B lymphocytes and T lymphocytes. Both of these cells come from the bone marrow; however, B cells come directly from the bone marrow and T cells need to be processed by the thymus. T cells are specifically involved in the cell-mediated immune response. Both types of cells have receptor molecules on their surfaces that recognize specific targets. T cells are able to recognize a pathogen only after parts of the pathogen called antigens have been processed and have been identified as nonself molecules. There are two major types of T cells. 10

These include the killer T cells and the helper T cells. There are also regulatory T cells that are involved in modulating the immune response. Killer cells can only kill antigens that are connected to Class 1 MHC molecules, while the helper T cells and regulatory T cells can only recognize antigens that are connected to class II MHC molecules. The role of the B cells is to make the antibodies that are ultimately connected to a specific antigen that has been identified as being part of a foreign pathogen or foreign cell. Each line of B cell is able to make only one type of antibody so that the body consists of millions of different lines of B cells—each of which expresses a specific antibody that can be produced in large numbers in a short period of time when needed at the outset of an invasion with a cell or microbe the body has encountered before. Killer T cells are specialized T cells that only kill cells that are infected by a virus or similar pathogen, although it can also kill a damaged cell. Each T cell has a specialized receptor that binds to an antigen on the MCH Class I receptor of another cell. If it recognizes the antigen as being part of the self, it leaves the cell alone. If it recognizes the antigen as being non-self, it releases cytotoxins, such as one called perforin, that forms holes in the other cell’s membrane, allowing ions to flow through the cell membrane, swelling and killing the cell. Another cytotoxin called granulysin is a protease that induces programmed cell death. These cells are particularly helpful in killing virally-infected cells. Helper T cells are a part of both the innate and adaptive immune systems. They help decide what response the immune system is going to make but don’t do any actual killing. They simply help other cells by expressing T cell receptors, which recognize antigens that are connected to Class II MCH molecules. It takes many receptors on a helper T cell to bind to the MCH antigen before it is activated, while killer T cells only need one receptor bound to the complex to be activated. B lymphocytes bind to antigens on a foreign pathogen and make an antibody that matches to the antigen. The B cell then displays the antigen on its MCH Class II molecules, which attracts a helper T cell that ultimately releases cytokines, activating the B cell. The B cell divides many times over, releasing antibodies that bind to pathogens, marking them for destruction. Antibodies can bind to bacterial toxins or to receptors on pathogens so they can be destroyed.

Passive Immunity Passive immunity is the type of immunity endowed upon newborns and babies who breastfeed. They have no prior exposure to microbes and get their immunity from IgG antibodies passed through the placenta or in breastmilk that are specific to certain infectious diseases. This keeps the baby temporarily from getting an infection that it has no previous experience with. It is just temporary and does not produce any B cells in the newborn or fetus, making it an immune 11

response that lasts only a few days. Antibody-rich serum can be given to a person medically to give them a type of passive immunity as well.

Active Immunity Active immunity can be conferred by having the infection or by being immunized against the pathogen by means of a vaccination. Vaccination or immunization involves providing an individual with an antigen that is biologically inactive or inert. The person makes B cells that produce antibodies against the antigen, giving immunity against a particular organism. This deliberate activation of the immune response is part of what prevents many diseases in today’s modern world. Viral vaccines can be killed viruses or live attenuated viruses, while bacterial vaccines are a cellular pieces of the bacterium or a harmless component of a bacterial toxin.

Key Takeaways • • • • •

There are many layers to the immune response, beginning with the barrier layer that keeps pathogens from invading in the first place. The innate immune system is not specific to a particular organism but acts to destroy pathogens in a nonspecific way. The adaptive immune system involves being exposed to a pathogen and making antibodies that later remember being infected by the organism. There are many different types of cells and molecules necessary to mount an adequate immune response. Passive immunity is conferred to a fetus or baby through the placenta or breastmilk, providing a temporary type of immunity to infections the baby has never been exposed to before.

Quiz 1. Which infectious organism is not usually able to pass through normal skin? a. b. c. d.

Strongyloides Streptococcus Human papillomavirus Schistosoma Answer: b. All of the above species of organisms are able to penetrate the skin’s natural barrier defenses, except Streptococcus species, which usually is repelled by the skin barrier.

2. What is an added way that the respiratory barrier fights off microbes? a. b. c. d.

It secretes an enzyme that digests bacterial cell walls. It has phagocytes outside of the respiratory tract that digest microorganisms. It has cilia that transport microbes away from the lungs. It secretes amylase that is toxic to invading bacteria. Answer: c. The respiratory tract has cilia that transport bacteria and other microbes away from lung tissue.

3. What is the main way that the stomach fights off bacterial invasion? a. b. c. d.

Enzymes are secreted that kill off bacterial organisms Peristaltic activity in the stomach pushes bacteria out of the stomach’s interior The cells of the stomach secrete IgA antibodies that attack microorganisms The low pH of the stomach is antibacterial in nature Answer: d. The stomach acts to fight bacteria by having a low pH that is antibacterial in nature.

4. There are many ways in which organisms fight off disease and destroy pathogens. What is the dominant immune system found in most organisms, including nonvertebrates? a. b. c. d.

Barrier systems The complement system The innate immune system The antibody system Answer: c. The innate immune system is nonspecific and not long-lasting but it remains the dominant type of immune defense found in most organisms in both the plant and animal world.

5. Cytokines are important parts of the human innate immune response. Which type of molecule is not considered a type of cytokine? a. b. c. d.

Chemokines Interleukins Interferons Prostaglandins

Answer: d. All of the above are considered cytokine molecules, with the exception of prostaglandins, which also act in the innate immune system but are not cytokines. 6. Symbiotic microflora in the gut involve what aspect of the immune system? a. b. c. d.

Barrier immune system Humoral immune system Innate immune system Adaptive immune system Answer: a. Symbiotic microflora in the gut are part of the barrier immune system and are present so that pathogenic bacteria and other types of microorganisms don’t take hold.

7. What is the main killing action that makes the innate immune system so effective? a. b. c. d.

Antibody-targeted cell membrane destruction Proteolytic activity against pathogens Phagocytosis of pathogens Complement destruction of pathogens Answer: c. Phagocytosis of pathogens is the main way that the innate immune system acts to kill off pathogens in a nonspecific way.

8. What organelle inside a macrophage is responsible for the actual destruction of a foreign pathogen? a. b. c. d.

Peroxisome Lysosome Mitochondrion Golgi apparatus Answer: b. it is the lysosome that combines with a vesicle containing a pathogen that ultimately allows for the destruction of the pathogenic organism or pathogenic particle.

9. Which type of cells are the first to reach the site of an infection or a breach in the barrier immune system? a. B lymphocytes b. Neutrophils c. Macrophages 14

d. Mast cells Answer: b. It is the neutrophils that arrive first at the site of an infection or breach in the barrier immune system, after which they participate in phagocytosis to begin the process of controlling the invasion. 10. Which type of molecule is involved in the provision of passive immunity? a. b. c. d.

Cytokine IgG antibody Chemokine Histamine Answer: b. An IgG antibody molecule is passed from mother to infant or fetus to provide passive immunity to the child on a temporary basis.