REPERTOIRE OF CD5- CORD BLOOD B-CELLS - SPECIFICITY AND EXPRESSION OFV(H)I AND V(H)III ASSOCIATED IDIOTOPES( AND CD5)

Epstein-Barr (EBV)-immortalized B cell clones were established from CD 5+ and CD5- cord blood B cells separated by flow cytometry. We have pr eviously shown that IgM from many of the clones was polyreactive, exhi biting reactivity with a number of autoantigens. In this study, IgM pr oduced by the clones was analysed by MoAb for the expression of cross- reactive idiotypes (CRI) associated with rheumatoid factor paraprotein s and from defined V(H) and V(K) subgroups of immunoglobulin heavy and light chains. IgM produced by clones established from CD5+ and CD5- B cells expressed the V(H) I associated idiotope G8. Furthermore, IgM p roduced by both sets of clones exhibited a similar frequency of V(H) I II heavy chain subgroup expression, as determined by reactivity with s taphylococcal protein A (SpA) and V(H) III-associated CRI expression ( B6 and/or D12). In contrast, expression of the V(kappa) III-associated 17.109 CRI was significantly higher in IgM antibodies produced by clo nes established from CD5+ compared with the CD5- clones (32 versus 5%: P < 0.05). Analysis of the V(H) and V(L) subgroup expression by IgM p roduced by the CD5+ and CD5- cord blood clones, and their autoantigen reactivity profile did not reveal restriction or selection within CD5 and CD5- populations. However, our data suggest that differences may exist in the expression of certain germline genes between CD5+ and CD5 - cord blood B cells and might indicate an expansion of CD5+ B cells w ithin the fetal environment.