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15.3: Unique Characteristics

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    Three characteristics of the immune system make it unique among the body's defense mechanisms. First, it shows self-recognition, which means that the immune system attempts to distinguish between substances that are normal constituents of a person's body and substances that are foreign to it. Upon identifying a substance as foreign, the immune system mounts an immune response against it. It can perform an immune response against some types of cancer cells because they display molecules identified as foreign. Any substance that causes an immune response is called an antigen.

    The second unique characteristic is specificity, which means that an immune response will operate only against one antigen. Therefore, a different immune response must be produced each time a different antigen is encountered. For example, specificity explains why an immune response against the virus that causes measles provides no protection against the virus that causes chickenpox. In contrast to the immune system, other bodily defense mechanisms against harmful chemicals, microbes, viruses, and cancer cells are called nonspecific because each mechanism helps protect the body against a variety of these agents. Some nonspecific defense mechanisms, such as the skin, mucous membranes, and mucus, prevent harmful agents from entering the body, while others, such as movements of cilia, defecation, and urination, help expel them. Other mechanisms, such as fever, perspiration, sebum, and acidic conditions in the stomach and vagina, inhibit the growth of harmful microbes. Finally, phagocytic cells (e.g., WBCs) and natural killer (NK) cells act nonspecifically in killing microbes and cancer cells.

    The third unique characteristic is memory. When the immune system responds against an antigen, it develops a residual set of lymphocytes called memory cells and usually develops a group of long-lasting antibodies. Antibodies are protein molecules that adhere to antigens and help combat them. Each time a particular antigen is encountered, the memory cells and antibodies developed for that antigen cause a quicker and more intense attack and thus eliminate it faster. In contrast, nonspecific defense mechanisms function with the same speed and intensity each time an injurious agent presents itself, allowing for the same risk of injury from the agent before it is eliminated.

    This page titled 15.3: Unique Characteristics is shared under a CC BY-NC-SA 4.0 license and was authored, remixed, and/or curated by Augustine G. DiGiovanna via source content that was edited to the style and standards of the LibreTexts platform; a detailed edit history is available upon request.