B cell differentiation antigens as probes for functional B cell subsets.

In this review I have discussed the serological, biochemical and functional characterization of two differentiation antigens, Lyb3 and Ia. W39, which have the same time distribution; namely, they are selectively expressed on a late maturing subset of B cells (Lyb3 and Ia. W39) and antigen presenting macrophages (Ia. W39, Lyb3?) Antisera against both determinants were raised in xid defective F1 male mice, which were immunized with spleen cells from the normal parent. Lyb3 is an isogenic specificity expressed without allelic forms in all mouse strains, whereas Ia.W39 is a private specificity, encoded by a gene(s) within the I-Ab subregion of the H-2 complex. Interestingly, the xid gene does not control the synthesis of these differentiation antigens, but affects their membrane expression (shown for Ia. W39.) Lyb3 is a polypeptide of 68,000d MW which has a similar IE point in all mouse strains. The molecule bearing Ia. W39 has an identical 2-chain structure (a and beta) and 2-D gel profile as the molecule expressing all the conventional Ia specificities encoded by the I-Ab subregion. However, from the difference in the ontological appearance and the turnover rate and from sequential immunoprecipitation studies we concluded that there are two kinds of glycoproteins containing Aa and Abeta chains; both would express the conventional specificities, and one would, in addition, bear Ia. W39. Functionally, we have defined Lyb3 as a receptor for triggering signals and Ia. W39 as a specific Ir gene epitope.