HETEROGENEITY OF BOVINE IGG2 .6. COMPARATIVE SPECIFICITY OF MONOCLONAL AND POLYCLONAL CAPTURE ANTIBODIES FOR IGG2A(A1) AND IGG2A(A2)

The relative specificity of 26 randomly selected polyclonal and monocl onal 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 signi ficantly allotype-biased and > 80% of those were positively biased to IgG2a (A1). Compared as the ratio of the ng ofIgG2a(A1) bound versus n g IgG2a(A2) bound per 50 ng added (K-rel), bias for IgG2a(A1) of six o f these reagents was greater than two-fold. Compared in terms of their solid-phase equilibrium constants (K-eq), differences as great as two -logs among these reagents were observed. Steward-Petty plots suggeste d that differences in K-rel of a select panel of reagents was usually due to differences in K-eq, but for two reagents with large difference s in K-rel, the existence of one population of CAbs recognizing an all otope and another recognizing common IgG2a determinants, was indicated . Eight of ten guinea pigs immunized with IgG2a (A1) responded with hi ghly significant specificity bias for A1 whereas only two of 11 rabbit s and two of ten guinea pigs immunized with IgG2a (A2) responded weakl y with preference for IgG2a(A2). These results concur with the concept of the immunodominant nature of the A1 allotope, but also suggest tha t immunization with IgG2a(A2) might be a practical means of avoiding a llotype bias in IgG2a reagents. The data indicate that the majority of randomly selected anti-bovine IgG2 reagents are allotype biased to th e extent that when used as serological reagents to measure total IgG2 or bovine IgG2 antibody responses, the allotype of the animal tested r ather than its total IgG2a concentration or IgG2 antibody titer, can d etermine the outcome of the serological test.