Microbiology

Microbiology Study Guide

4.3 Principles of Immunology Antigens Antigens, also known as immunogens, are the foreign substances that encourage a response from the immune system. Most antigens have high molecular weights, but the ones with lowmolecular weight, known as hapten, are also likely to act if they are able to fuse and react with proteins present in the body. This fusion of the hapten with the proteins of the body can encourage the immune system to respond against the antigens. One of the most critical steps undertaken by the immune responses is the processing of these antigens by macrophages in the body tissues. However, the ingestion of the microorganisms, or antigens, may not invoke the response from the immune system, as there is a possibility that the antigen substances are broken down into several pieces before they are ingested by the macrophages. Antigenic Determinants Antigenic determinants are comprised of the cells and molecules of the chemical groups that help to determine the immunogenicity. These are also called epitopes. Epitopes are generally made up of amino acids, but may consist of a number of monosaccharides or a polysaccharide. Every species has different antigens due to the differences in carbohydrates, proteins, and other organic matter. Types of Antigens There are different types of antigens depending upon their nature and function. The most important one is autoantigens, which are natural and are the antigens themselves. The antigens that are found in different organisms of the one same genre of species are known as alloantigens. For instance, antigens A and B of red blood cells are alloantigens. The heterophile antigens are the same antigens but are found in different species. In other words, these are the common antigens shared by different species. Antigens can also be categorized on the basis of their presence on the body. Somatic antigens are the antigens which are found on the cells of the body. Those antigens, which are encapsulated in the bacterial capsule walls, are termed as capsular antigens. H antigens, or flagellar antigens, are the ones which are produced on the flagella of the organisms. It should be noted that the substances of protein, like exotoxin, are also antigenic. The Immune System The immune system acts as a major barrier to organisms causing infection. One of the most vital features of the immune system is the specific resistance, which acts as a defense against a specific type of microorganism in the body. The role of the immune system is to recognize the presence of any foreign substance in the body and consider it as a “non-part” of the body. Upon recognition, the immune system takes necessary actions

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