4) Antimicrobial Proteins (AMPs): kills microbes or inhibits growth
Short peptides with a broad spectrum of antimicrobial activity. Examples are produced in sweat glands, produced by neutrophils, macrophages, produced by platelets. Microbes exposed to AMPs DO NOT develop resistance which is always the case with antibiotics.
B) Natural Killer Cells (NKs)
If microbes penetrate the skin and mucous membranes or bypass antimicrobial substances in the blood, the next nonspecific response is Natural Killer Cells and Phagocytes. ~5-10% of lymphocytes in the blood are NKs. They are also present in the spleen, lymph nodes, and red bone marrow. NKs kill a wide variety of infected body cells and certain tumor cells. They attack ANY body cell that displays abnormal or unusual plasma membrane proteins. NKs bind to a target cell and release granules containing toxic substances. Some granules contain a protein that attaches to an infected cell and creates channels into the cell. Subsequently, extracellular fluid flows into the infected cell and it bursts (Cytolysis). Other granules release enzymes that induce the infected cell to undergo Apoptosis or self-destruction. This releases the microbes inside which are destroyed by waiting phagocytes.
C) Phagocytes
These are specialized cells that perform phagocytosis which is the ingestion of microbes or other particle such as cellular debris. The two major types are: Neutrophils and Macrophages . When infection occurs, these cells migrate to the infected site. These are wandering macrophages. Others are fixed macrophages standing guard over specific tissues.
Phagocytosis occurs in 5 phases :
Chemotaxis: chemically stimulate movement of phagocytes to site of damage Adherence: phagocyte and microbe attach Ingestion: phagocyte engulfs microbe Digestion: phagocyte merges with lysosome, releases enzymes to break down microbial walls Killing: chemicals and enzymes kill microbe
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