DETECTION OF ANTIVIRAL ANTIBODIES IN SERUM USING AN ELISA TECHNIQUE - Essay Example

These immunoglobulins are of five types and they are different based on size, charge, amino acid composition and carbohydrate content. the class and the type of immunoglobulin molecule is determined by the heavy chain type. There are two light chains and two heavy chains. There are C and N- terminal in the heavy chains. (Crowther 1995). The N-terminals of the IgG constitute the antigen -binding site. Individuals can become resistant to many infectious diseases by active or passive immunization.

The beneficial effects of the immunization are mediated by the antibodies and the effect of immunization is mediated by the immunoassays. (Crowther 2001). The measurement of the antigen and antibody by using sensitive assays are the useful indicators of the immune status. When an infectious agent enters the human body, the component is identified as the foreign particle and antibodies are produced against them. These antibodies interact with the antigens and reduce the load. (Edwards 1999). The immunoassay method identifies the antigens, antigen - particles present in the blood and provide the results.

Each antibody is specific for an antigen. ELISA is basically of two types: competitive and non-competitive ELISA. ELISA involves two site recognition with two different antibodies (i.e.) an indirect estimation. Competitive ELISA is different from the sandwich ELISA and indirect ELISA. In the first step the unlabelled antibody is incubated on the presence of the antigen. This antigen-antibody bounded is added to the antigen- coated well. The plate is washed and the second antibody specific to the primary antibody is added and the second antibody is coupled to the enzyme.

When the substrate is added, the signal is emitted by the remaining enzyme. In this ELISA, if the antigen concentration is very high, then the signal will be very weak. This method is mainly used to test the impure and crude samples. This method is very useful for the detection of HIV. For HIV diagnosis, the patient's sample and the enzyme-labeled antibody (conjugate) is added simultaneously to the solid phase. HIV antibodies, if present in the sample will bind to the conjugate antibody and reduce the signal.

Thus if the color reaction is produced, then it indicates that there are no HIV antibodies in the given sample. Applications of ELISA include screening of the donated blood for viral contaminations( HIV types, Hepatitis B and C, HTLV-1 and 2), measuring the hormone levels( pregnancy(HCG), ovulation( LH), thyroid function ( TSH, T3 and T4), anabolic steroids, hormones), detecting infections( HIV, syphilis, chlamydia, gondii), detecting allergens in foods and toxins in foods, measuring the concentration of the antibodies and detecting illicit drugs ( cocaine, opiates, marijuana, etc.), measuring auto antibodies in autoimmune diseases and measuring rheumatoid factors .

(Sheehan 1997). (Wreghitt and Morgan-Capner 1990). Principle When an antibody is linked to the enzyme and allowed to react with the immobilized antigen, antigen-antibody reaction occurs. This is identified by the production of colour by the substrate enzyme reaction. The antigen is immobilised in either a microtiter plate or on nitrocellulose membrane. An enzyme labelled antibody is added in excess to the system and these binds to the immobilised antigen. Excess antibody is removed by washing and the substrate specific for the