Principles of Immunochemical Techniques

The binding of antibodies and their complementary antigens forms the basis of all immunochemical techniques. 

The variable amino acid sequence at the amino terminal end of each chain determines the antigenic specificity of the particular antibody. Each unique amino acid sequence is a product of a single plasma cell line or clone. The normal host response to an immunogen results in the stimulation of one or two major classes of lymphocytes that are able to divide and produce plasma ceUs capable of secreting antibodies. Each plasma cell line produces antibodies with a single specificity. A complex antigen is capable of eliciting a multiplicity of antibodies with different specificities that are derived 

An immunogen is either a protein or a substance coupled to a carrier, usually a protein, that when introduced into a foreign host is capable of inducing the formation of an antibody in the host. The route of introduction of the immunogen is usually, but not always, intradermal. The antibody produced may be either circulating (humoral) or tissue bound (cellular), as in delayed hypersensitivity reactions or graft host reactions. 

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Immunoassay methodologies are now a major method for rapid analysis of many mycotoxins, especially aflatoxins. These immunochemical techniques are based upon quite different principles to chromatographic procedures. In essence, immunochemical procedures involve reversible binding between antigens (the... 

The author s aims are a) to classify as rationally as possible the techniques of immunochemical analysis by antigen-antibody precipitation in gels (,b) to state the more or less general principles and laws which hold true for all or part of the techniques (c) to help the reader in understanding the bases of the different techniques in a way that does not require any special knowledge of physics and (d) to give a few examples to illustrate that this understanding of the principles and laws, plus an analysis of the reactions may raise, and eventually solve, problems of appreciable importance. 

A most important technique which has been developed as an extension of the isotope dilution principle is that of radioimmunoassay (RIA). Analyses by this method employ substoichiometric amounts of specific binding immuno-chemical reagents for the determination of a wide range of materials (immunogens) which can be made to produce immunological responses in animals such as sheep or rabbits. It is possible to combine the specificity of an immunochemical reaction with the extreme sensitivity of radiotracer detection. Analytical methods based upon these principles have achieved wide applicability in the determination of organic compounds at trace levels. 

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