THE GENETIC-BASIS OF HUMAN VH4 GENE FAMILY-ASSOCIATED CROSS-REACTIVE IDIOTYPE EXPRESSION IN CD5- CORD-BLOOD B-LYMPHOCYTE CLONES( AND CD5)

In a recent study we have observed a high frequency expression of cros s-reactive idiotypes encoded by genes from the relatively small V(H)4 family of immunoglobulin heavy chain genes in cord blood B-lymphocyte lines. Furthermore, we have demonstrated a selective pattern of expres sion of two V(H)4-associated cross-reactive idiotype (CRI) in B-lympho cyte lines established from CD5+ and CD5- cord blood B-lymphocytes. Th ere was a restricted expression of one CRI marker recognized by the 9G 4 monoclonal antibody in lines established from CD5+ B-lymphocytes but not in those established from the CD5- population. In the current stu dy we examine the molecular basis for the selective pattern of CRI exp ression. Nucleotide-sequence analysis of functional immunoglobulin hea vy chain (IgH) gene rearrangements in three CD5 + lines expressing the CRI recognised by 9G4 reveal that all use a single gene from the V(H) 4 family, the V4.21 gene. However, all three lines have distinct third complementarity determining regions (CDR3) implying different clonal origins. In contrast, four cord blood cell lines (two established from CD5+ B-lymphocytes) expressing the CRI recognized by MoAb Lcl have fu nctional IgH gene rearrangements involving two different genes from th e V(H)4 family, the V71-4, and V2-1 genes. Antigen specificity analysi s reveals that all three 9G4-reactive lines produce antibodies that re act with the I and/or i red blood cell carbohydrate antigens. These da ta suggest that the distinction in V(H)4 gene use in CD5+ B-lymphocyte s in cord blood results from a selection process in vivo that shapes t he repertoire of CD5+ B-lymphocytes. This study extends recent observa tions that the monoclonal anti-CRI antibodies 9G4 and Lc1 are markers of two distinct subgroups of proteins encoded by two subsets of genes within the V(H)4 family. Furthermore, it appears that amino acid resid ues in framework region one and complementarity determining region two are critical for the expression of the cross reactive idiotypes and t he serological distinction between the two subgroups of proteins.