Lysis Complement Fixation

Lysis Complement Fixation

	Lysis Complement Fixation The somatic antigens of certain types of cells produce antibodies that assist in the lysis of that cell. These antibodies are termed cytolysins. The cytolytic antibody first combines with specific antigens on the surface of the cell that produced it. The cell may be a bacterium (bacteriolysis) or an erythrocyte (haemolysis). This simple combination is, however, not sufficient to destroy the cell. To bring about the lysis of a cell, not only specific antibodies, but a nonspecific unstable component of fresh serum is also required. This non specific component is termed complement.
The complement system has not been fully characterized but it is known to consist of a group of eleven serum proteins, and is present in the serum of normal individuals. The complement of most species reacts with antibody, derived from other species. The common laboratory source of complement is guinea pig serum. If complement interacts with an immune system involving antigens that constitute part of the cytoplasmic membrane of a cell, irreversible cell damage can occur which may result in the lysis of that cell. Although only a few manifestations of antigen antibody reactions depend on the presence of complement, the complement components become bound and are inactivated in almost any immune system. Complement is then said to be fixed.
This phenomenon forms the basis for a very sensitive test that can be used to detect and quantitate antigens and antibodies. The test involves two stages in the first stage, the test antigen and the antiserum (heated to 56°C to inactivate native complement) are mixed in presence of a known amount of complement (guinea pig serum). It is incubated at 4°C for 18 hours. If antibody specific for the known antigen is present in the serum, antigen antibody complexes will be formed that will fix all the complement. However, this reaction cannot be seen. In the second stage, an indicator system is added to test for the presence of free complement.
The indicator system consists of sheep red blood cells plus antibody (haemolysin) specific for sheep red cells. If all of the complement has been fixed, none will be free to lyse sheep red cells (positive complement fixation test). If no antibody is present in the patient’s serum, then the complement is not fixed and is free to interact in the indicator system and lyse the red cells (negative complement fixation test). Properly conducted complement fixation tests require the incorporation of appropriate controls to assure that the results will not be adversely affected by the presence of anticomplementary ingredients. The antigen or the serum itself may have anti complementary properties mediated by, for example, denatured immunoglobulin, heparin, chelating agents, or microbial contaminants. It is absolutely essential that all reactants in the test are accurately adjusted, complement fixation is very useful technique in immunology because it is highly sensitive. Small amount of antigen or antibody are required in the test.
	Also, some immune systems do not cause visible or measurable changes, and complement fixation may be used as an indirect measurement of such reactions. In other words, almost any antigen antibody reaction can be measured in this way. The test is widely used in the laboratory diagnosis of many infectious diseases, including those of bacterial, viral, protozoan, and fungal etiology it is also used for the identification of many microorganisms one of the best known applications of the complement fixation test is Wasserman test for syphilis.

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