Heterogeneity of bovine IgG2. VI. Comparative specificity of monoclonal and polyclonal capture antibodies for IgG2a (A1) and IgG2a (A2).

The relative specificity of 26 randomly selected polyclonal and monoclonal anti-bovine IgG2 reagents for the A1 and A2 allotypic variants of IgG2a was evaluated in a direct RIA using the reagents as solid-phase capture antibodies (CAbs). More than 70% of these reagents were significantly allotype-biased and > 80% of those were positively biased to IgG2a (A1). Compared as the ratio of the ng of IgG2a (A1) bound versus ng IgG2a (A2) bound per 50 ng added (Krel), bias for IgG2a (A1) of six of these reagents was greater than two-fold. Compared in terms of their solid-phase equilibrium constants (Keq), differences as great as two-logs among these reagents were observed. Steward-Petty plots suggested that differences in Krel of a select panel of reagents was usually due to differences in Keq, but for two reagents with large differences in Krel, the existence of one population of CAbs recognizing an allotope and another recognizing common IgG2a determinants, was indicated. Eight of ten guinea pigs immunized with IgG2a (A1) responded with highly significant specificity bias for A1 whereas only two of 11 rabbits and two of ten guinea pigs immunized with IgG2a (A2) responded weakly with preference for IgG2a (A2). These results concur with the concept of the immunodominant nature of the A1 allotope, but also suggest that immunization with IgG2a (A2) might be a practical means of avoiding allotype bias in IgG2a reagents. The data indicate that the majority of randomly selected anti-bovine IgG2 reagents are allotype biased to the extent that when used as serological reagents to measure total IgG2 or bovine IgG2 antibody responses, the allotype of the animal tested rather than its total IgG2a concentration or IgG2 antibody titer, can determine the outcome of the serological test.