Immune System Quiz

Explain how the immune system achieves all of the following


1. Provides an immediate nonspecific immune response


The immune system presents physical barriers, such as skin and mucus membranes, that prevent foreign substances (pathogens) from entering the body. The mucus traps microbes (bacteria microorganisms that cause disease) and sweeps them away, without knowing specifically what that bacterium is. Some more examples are blood clots in wounds (in which inflammation occurs and a large amount of white blood cells are brought in to fight whatever infection exists in that infected area), or flushing of tears or saliva (which wash away pathogens), all of which prevent infection. Two other examples, vomiting and diarrhea, both help get rid of harmful germs. Unfortunately, some substances, such as peanuts, can cause allergic reactions because your body attacks it as it would a virus. 




With infection or injury, inflammation occurs and phagocytes, which ingest harmful germs, are brought to that area. The complement system is activated. Many chemical agents are involved, such as Histamine, which allows for more white blood cells. There are also interferons, which limit virus replication, pyrogens, which cause fever to inhibit bacteria, lysozyme, which breaks down cell walls, and lactoferrin, which limits bacteria growth.

In addition to physical barriers, there are also chemical barriers, such as fatty acids in sweat that prevents bacteria growth. Lysosomes and phospholipase in mucus, saliva, and tears all break down cell walls, killing pathogens. 

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2. Activates T and B cells in response to an infection


MHC molecules (Major Histocompatability Complex) are on the surface of most cells in the body. These MHC molecules interact with the T-receptor on T-cells and help these T-cells to recognize antigens, such as a virus. The MHC molecules bind to virus antigens on infected cells. This antigen presenting cell binds helper T-cells to activate helper T-cells or cytotoxic T-cells. Helper T-cells either activate cytotoxic T-cells or stimulate B-cells.




The T-cell signals the B-cell using cytokines to make a unique antibody that can kill a certain harmful antigen. Interleukin 1 from macrophages activate helper T-cells and Interleukin 2 from helper T-cells activates cytotoxic T-cells or B-cells.

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3. Responds to a later exposure to the same infectious agent


Some of the T-cells and B-cells from the initial infection differentiate into longterm "memory cells", which are specific for the same harmful antigens that were previously seen. Therefore, those memory cells are more attracted to these antigens and respond faster and to a larger extent.




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4. Distinguishes self from non self


Every cell in the body carries distinctive molecules that identify it as self. This set of unique molecules, or markers, are called major histocompatability complex (MHC) molecules. There are MHC I proteins that are on all cells, and MHC II proteins only on specialized cells. Nonself markers that cause an immune response are called antigens, which can be viruses, bacteria, portions of foreign proteins, or a MHC marker protein.

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