Cellular Defense

molecules together will cause vomiting, diarrhea, and coughing, which help to get rid of pathogens from the body.

Some cytokines will trigger the production and release of prostaglandins. Prostaglandins increase the body temperature, which increases white blood cell activity and blocks the growth of bacteria. Bradykinin can be released as well, which causes tissue edema in an area of infection.

CELLULAR DEFENSE

There are many cells that contribute to the immune response. All cells in the bloodstream are made in the bone marrow by stem cells in the differentiation process called hematopoiesis. Most stem cells make red blood cells but there are others that make platelets, lymphocytes, neutrophils, basophils, monocytes, and eosinophils. Monocytes further differentiate into dendritic cells and macrophages. Lymphocytes further differentiate into natural killer cells, T lymphocytes, and B lymphocytes, which later mature to become plasma cells. Figure 52 shows the hematopoietic process:

Figure 52.

The three types of granulocytes are neutrophils, eosinophils, and basophils. These all have granules that get released as part of the immune response. Neutrophils participate in phagocytosis and are important to the overall immune response. They make defensins and enzymes that destroy bacteria. Pus is a collection of neutrophils at the site of infection along with cell debris and dead bacteria. Eosinophils are important in fighting helminths and protozoa; they also participate in the allergic response. Basophils release histamine as part of the immune response.

Mast cells are derived from the same cells that make granulocytes. They also release histamine, heparin, and leukotrienes. The reside in tissues rather than in the bloodstream like basophils do. They are found near mucous membranes and near the skin.

Agranulocytes do not have visible granules and can be either monocytes or lymphocytes. Lymphocytes make natural killer cells or NK cells, which are crucial to the innate immune system. Lymphocytes involve B cells or T cells, which are more important to the adaptive immune response, which will soon be discussed. Monocytes make dendritic cells and macrophages, which also participate in phagocytosis like neutrophils.

Natural killer cells or NK cells can destroy abnormal cells. Virally infected cells and cancer cells are two types of cells that are killed by natural killer cells. They can recognize normal cells by their receptors and generally leave them alone. Damaged cells are recognized as being abnormal and will be killed. It is the major histocompatibility I complex that needs to be recognized as belong to the self so as to avoid destruction by NK cells.

Natural killer cells can do several things. They can cause apoptosis, which is controlled cell death or cellular suicide. They can release perforin, which is a protein that causes pores in the target cell, killing it. They can also release granzymes, which are proteases that get into the pores and trigger cells to be killed from the inside.

Monocytes are large while blood cells that are not granulocytes. They can differentiate into macrophages and dendritic cells that reside in the tissues and participate in phagocytosis. Macrophages can last in a specific tissue for a long period of time. They also release cytokines that are involved in the immune response. Tissue-resident