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If the known antigens are on red blood cells, Zeta potential

may need to be reduced in order to increase the affinity

between the epitopes on the antigens and the paratopes.

Paratopes are present on the antibodies, specifically the variable

portion of the Fab fragments where there is a single light chain

and a single heavy chain. This is also the location of the idiotype.

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Testing for immune complexes depends on the presence of an optimal antigen-antibody ratio. The concentration of antibodies is too high in a prozone phenomenon, and the antigen concentration is too high in a postzone phenomenon. Both will prevent optimal reactions and may yield false negative tests.

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When the patient sample is added, any antibody with the specificity to the antigen should attach. These antibodies have attached enzyme.

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Then anything that is not bound to the antibodies is washed out of the well.

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A substrate is added that will react with the enzymes present on the antibodies.

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This reaction causes a color change. More intense reactions indicate a higher concentration of antibodies.

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A direct immunoassay is used to test for the presence of an antigen-antibody

reaction. A common form of a direct immunoassay used is the direct ELISA.

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Enzyme-Linked ImmunoSorbent Assay

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Click on this tile and then scroll down and click on "Source" to test yourself.

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Before the patient sample is added to the well, it is coated with a known antigen that will form an antigen antibody complex with the antibodies for which the patient is being tested.