Reverse single radial immunodiffusion for estimation of titre of anti IgG antibody.

Reverse Single Radial Immunodiffusion (SRID) for estimating titre of anti IgG antisera is reported. Unlike the conventional radial immunodiffusion, the antigen (IgG) is held immobile in the gel while the antibody (Anti IgG) diffuses radially from the well (7 microliters) and the diameter of the resulting immuneprecipitates after immunodiffusion at 4 degrees C for 24 hr, represents a linear correlation with the antibody titre. The procedure was standardised by an extensive trial and error employing different concentrations of human IgG in the gel (60-240 micrograms) against varying dilutions of the standard antibody (titre: 3.8 mg/ml). The best results were obtained at 80 micrograms of IgG in the gel. The locally raised rabbit anti IgG antisera displayed a distinctive titre pattern under optimised conditions. Technical reproducibility, high-sensitivity threshold (0.25 mg/ml), simultaneous visual scrutiny of several antibody batches at a glance and ability to assess the shelf life of the stored antisera are its distinct assets.