B-CELLS IN THE BURSA OF FABRICIUS EXPRESS A NOVEL C-TYPE LECTIN GENE

The avian bursa of Fabricius provides an essential microenvironment fo r B cell development and Ab repertoire expansion by a gene conversion mechanism, To explore regulatory interactions between B lineage cells and the bursal microenvironment, we sought to identify genes encoding cell surface molecules selectively expressed on bursal B cells. We rep ort in this work the identification of the chB1 gene that encodes a C- type lectin molecule that is a distant relative of the mammalian B cel l differentiation Ag, CD72. The chB7 gene is expressed by intrabursal B cells and a B cell line, DT40, that also diversifies its Ig V region genes by gene conversion, Two forms of this type II membrane protein, differing in their cytoplasmic domains, are generated by the differen tial usage of two translational initiation sites, The longer chB1 isof orm, which is the most abundant, contains a consensus immunoreceptor t yrosine-based inhibitory motif in its cytoplasmic domain, Cross-linkag e of the chB1 molecules inhibits proliferation of bursal B cells and t he DT40 cell line. The chB1 lectin-like molecule may thus modulate int rabursal B cell development.