Differences in the cell binding affinity of a cross-reactive monoclonal anti-Ia alloantibody in mice of different H-2 haplotypes.

The analysis of an Ia specificity was performed in several H-2 haplotypes by evaluating the affinity of the binding to mouse spleen cells of a monoclonal anti-Ia alloantibody. We used the monoclonal antibody 10-2.16 (Oi et al., Curr. Top. Microbiol. Immunol. 1978. 81: 115.) which recognizes on I-A gene products a public specificity common to several H-2 haplotypes (f, ja, k, r, s and u). One parameter of the affinity (dissociation rate constant) was determined by the kinetics of the dissociation of cellbound 125 I-labeled Fab fragments in the presence of homologous antibodies. The dissociation rate constants thus obtained were different when the antibody reacted with cells from mice bearing different haplotypes and were similar for reactions with different mouse strains bearing the same haplotype. These data strongly suggest that the Ia public determinants involved are not strictly identical in different haplotypes, and support the concept that a serological cross-reaction does not necessarily mean structural identity between public antigenic determinants.