Comparison of diffusion-in-gel enzyme-linked immunosorbent assay with conventional serological methods for detection of class-specific antibodies to Salmonella typhi O antigen.

The diffusion-in-gel enzyme-linked immunosorbent assay (DIG-ELISA) is a new and simple method for quantitation of antibodies, based on the ability of antibodies to diffuse from wells in gel and adsorb to antigen which is bound to a polystyrene surface. The antigen-antibody reaction is visualized with a color reaction caused by horseradish peroxidase-conjugated class-specific anti-immunoglobins. This method was used to study the immunoglobulin G, A, and M immune response to Salmonella typhi O antigen in individuals immunized with a monovalent heat-inactivated typhoid vaccine. The antibody values obtained by the DIG-ELISA method correlated with those evaluated by conventional direct agglutination (Widal) and indirect hemagglutination methods. The DIG-ELISA method was also found to be sensitive, specific, and economical, as well as suitable for handling large numbers of sera while requiring very simple equipment.