Serological Tests

Abstract

Serological tests are based on the reaction of antibody with antigen. Antibody specifically reacts with the antigen against which it is produced. A large number of serological tests are available for the detection and diagnosis of plant viruses. Traditional methods such as tube precipitin, microprecipitin, chloroplast agglutination and gel diffusion involved direct observation of specific precipitates of virus and antibody, either in liquid media or agar gels. These methods require large quantities of reactants---antiserum and antigens for successful detection. With the advent of enzyme-linked immunoassay (ELISA) during 1980s, traditional methods are replaced by this method. Various formats of ELSA such as double-antibody sandwich (DAS)-ELISA, F(ab)2-ELISA, plate-trapped ELISA, and direct antigen-coated (DAC)-ELISA are used widely for the detection and assay of plant viruses. It is very economical in the use of antiserum, adaptable for large-scale testing and quantitative measurement. ELISA performed on a nitrocellulose or nylon membrane is referred to as dot immunobinding assay (DIBA). Tissue blotting immunoassay (TBIA) is another simple method where crude sap from plants are directly blotted and used for detection through immunology. Immunosorbent electron microscopy (ISEM) combines electron microscopy and serology for the detection and diagnosis of viruses. Electro-blot immunoassay (EBIA) though cumbersome is a confirmatory assay that involves separation of viral antigens on a gel followed by its detection through serology. Lateral flow assay (LFA) or dip stick assay is the latest and the only serological method used for the detection of viruses without the aid of a laboratory and skilled technical personnel. It is an onsite and quick assay that can be performed by anyone and suitable for the detection of viruses that occur in high concentration in plants.