3. cytolysis – several complement proteins (C5b, C6-C9) come together to form a membrane attack complex that punches holes in the plasma membrane of microbes. Natural Killer cells (NK cells) are lymphocytes that have the ability to kill a wide variety of infectious microbes and tumor cells with no prior activation required. They are present in the spleen, lymph nodes, bone marrow, and blood. They kill cells by binding to them and releasing perforin, which causes cytolysis. Phagocytosis is accomplished by neutrophils and macrophages. When an infection occurs both cell types migrate to the infected area. Monocytes from the blood enlarge and develop into highly phagocytic macrophages, called wandering macrophages. Other macrophages are fixed in place and located in the skin, liver, lungs, brain, spleen, lymph nodes, and bone marrow. All the macrophages spread throughout the body is called the reticuloendothelial system. The process of phagocytosis has three phases: chemotaxis (chemical attraction of phagocytes to an area), adherence (attachment of cell membrane of phagocyte to the surface of the microbe or foreign material), and ingestion. Phagocyte lysosomes contain lethal oxidants such as superoxides which destroy the ingested microbe. Objective 7. Describe the signs of inflammation and the underlying processes. When cells are damaged, the response to tissue damage is called inflammation. The signs are redness, pain, heat, and swelling. Inflammation attempts to prevent microbial spread to other areas, mobilizes the body to fight the potential infection, and prepares the site for tissue repair. Three stages are vasodilation, phagocyte migration, and repair. Vasodilation allows more blood to flow through the damaged area and permits defensive materials in the blood to enter the injured area. It also helps remove toxic products released by invading organisms and dead cells. Phagocyte migration occurs in as little as two minutes in response to chemotaxic substances. Neutrophils arrive first and monocytes follow. Neutrophils predominate in the early stages, but tend to die off rapidly. Macrophages are more phagocytic and engulf damaged tissue, worn-out neutrophils, and invading microbes. Fever intensifies the effect of interferons, inhibits growth of some microbes and speeds by body reactions that aid in repair. Objective 8. Describe the two hallmarks of the immune system. Specificity – ability to distinguish self from non-self and also to generate a response to a specific pathogen Memory – previously encountered pathogens are recognized and a second encounter prompts an even more vigorous response. Objective 9. Define antigen and antigenic determinant. Any chemical substance that when introduced into the body is recognized as foreign is known as an antigen. Antigens have two important characteristics: immunogenicity (ability to provoke an immune response) and reactivity (ability to react specifically with the antibodies or cells
produced by the immune response). Antigens are usually proteins, but some large polysaccharides can be antigens. A microbe will usually have several substances associated with it that is antigenic. Specific portions of antigen molecules trigger immune responses. These regions are called antigenic determinants or epitopes. One antigenic molecule may have several
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- Fall '15