Immunity – ability of the body to resist infection, or overcome an invading organism.
Immunity can be innate or acquired.
Innate immunity – inborn, unchanging, and non-specific. Skin acts as a barrier. Stomach acid kills pathogens.
Lysozyme in tears.
Also – interferon helps prevent multiplication of viruses, and phagocytosis.
Phagocytosis • ‘cell – eating’ • foreign bodies are engulfed and destroyed • phagocytic cells: monocytes and macrophages • macrophages in connective tissue throughout body • macrophages have many lysosomes with digestive enzymes
1.Macrophage detects bacterium and moves towards it. 2. Phagocytes engulfs bacterium in a vacuole by infolding of membrane.
3. Lysosomes fuse with vacuole. 4. Lysosomes release enzymes which digest bacterium.
5. Bacterium products absorbed by phagocyte. *fig. 7.2 p.52*
• during infection, many phagocytes engulf many bacteria • dead bacteria and phagocytes accumulate at injury site forming pus • large number of immobile macrophages line liver, spleen and lymph nodes to remove foreign bodies from passing blood or lymph.
Acquired Immunity • natural or artificial • it is gained by immune system producing antibodies in response to foreign antigens Antigen – molecule recognised as foreign to body • antigen markers on body cells known by immune system as ‘self’ antigens • carried out by B and T-lymphocytes (white blood cells)
Naturally Acquired Immunity B-cells • made in bone marrow, and pass to lymph nodes • produce antibodies in response to foreign antigens Receptor sites on antibodies specific to particular antigen.
• helper T-cells patrol body and activate B and T-cells when foreign antigen present. • B-cells multiply rapidly • some produce antibodies, some become memory cells • receptor sites on antibodies join with foreign antigen rendering harmless *see fig. 7.5 p.54* • humoral response
T-cells (made in bone marrow, pass to thymus) • when cell becomes infected by pathogen, pathogen’s antigens become present on cell membrane • helper T-cells activate killer T-cells • killer T-cells have specific receptors which join with foreign antigens • killer T-cells release digestive enzymes to destroy infected cell. *see fig. 7.4 p.53* • cell-mediated response • made in bone marrow, pass to thymus
Primary Response • person is infected by pathogen for first time • latent period exists between antigen entering body, and antibodies being produced. • memory B and T-cells produced
Secondary Response
• on next exposure to antigen, memory cells are quickly stimulated to produce clones •antibody production is faster, higher concentration, response lasts longer, often prevents disease. * Fig. 7.5 p.55*
Artificially Acquired Immunity • body is injected with harmless dose of foreign antigen • induces Band T-cell production, and antibody formation • also causes production of memory cells.
Vaccines • antigen can be harmless form (smallpox/cowpox), weakened (polio), dead (cholera), or chemically treated (attenuated) (tetanus).
Active (Acquired) Immunity • protection gained by person making antibodies • natural or artificial
Passive Immunity • protection gained by person being given antibodies • effects are short-lived • natural or artificial
For each situation, say whether the immunity gained is passive/active, and natural/artificial. 1.Person catching cold
Natural active
2.Person given an injection of tetanus antibodies
Artificial passive
3.Breastfeeding
4.A polio vaccine
Natural passive Artificial active
Allergies Allergic reaction – over-reaction of immune system to a harmless substance • immune system produces antibodies, which connect with mast cells in connective tissue • mast cells secrete histamine • histamine causes runny nose, cough etc. • relived by antihistamine drugs * Fig. 7.6 p.57*
• all cells have antigen signature, any different antigens attacked by immune system • transplanted tissues must be as close as possible or are rejected by immune system Autoimmunity – immune system attacks own body cells, e.g. 1. Rheumatoid arthritis – cartilage in joints attacked 2. Multiple Sclerosis (MS) – myelin sheath around nerves attacked
ABO Blood Groups *Copy/Refer Fig. 7.7 p.58* • certain blood groups are non-compatible • if wrong blood groups are mixed, antibodies in person’s own blood attacks foreign cells • red blood cells clump together => agglutination *Fig. 7.8 p.58*