Antigen antibody generation

Cross-reactivity occurs when antigens share epitopes such that an antibody generated against one antigen will also recognize another. 

Product variants can also be generated by in-process procedures, such as those used for viral inactivation, for example. These procedures could alter the protein structure, forming new epitopes. These types of changes could potentially be detected by ELISA because of the specificity of the antigen-antibody interaction. In the case of vaccine production, an ELISA could be used to monitor viral inactivation. For this, a panel of MAbs, if available, could be used. 

As noted above, the specificity of the antibody-antigen reaction is critical for obtaining reliable, interpretable results. For this reason, the antibody has to be tested rigorously, and essential controls for antibody specificity should be included in any experimental design. A comprehensive discussion on antibody generation, specificity, and testing for immunocytochemical applications can be found in references (27-29) and, for specific applications, see Chapters 17, 50, and 51. 

Fig. 1. Diagram illustrating the molecular interactions of the PAP procedure. The PAP complex is comprised of horseradish peroxidase bound to an antiperoxidase antibody generated in the same animal species as the primary antibody which recognized the tissue antigen of interest. The primary antibody and the PAP complex are linked via a secondary antibody generated in a second animal species against immunoglobulin of the primary animal species (A, immunoglobulin , peroxidase enzyme).

Third, they can act as antigens and generate an immune response which may result in a lower effective concentration of the protein at its effector site (because some of it is bound to the antibody) or occasionally in a clinical allergic syndrome - most particularly if the protein has been derived in whole or in part from non-human DNA (mouse DNA is incorporated with human in some production systems and this tends to produce more common immunological... 

Antibodies can be combined with enzymes and color reagents or radioactive antigens to produce quantitative testing for drugs. The ELISA or Enzyme-Linked ImmunoSorbant Assay uses antibodies generated against the Ag to be tested for covalently linked to an enzyme which can catalyze a color change reaction such as the NADH to NAD conversion (Xmax at 340 nm). When the Ag-Ab complex is formed the enzyme is activated and the color can be detected. 

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