V(H)DJ(H) GENE-SEQUENCES AND ANTIGEN REACTIVITY OF MONOCLONAL-ANTIBODIES PRODUCED BY HUMAN B-1 CELLS - EVIDENCE FOR SOMATIC SELECTION

To understand whether the distinct V(H)DJ(H) gene utilization by natur al polyreactive Abs reflects the developmentally restricted Ig V(H)DJ( H) rearrangements putatively expressed by B-1 cells, we generated 11 ( 8 IgM, 1 IgG3, 2 IgA1), 7 (6 IgM, 1 IgG1), and 7 (2 IgM, 3 IgG1, 2 IgG 3) mAb-producing lines using B-1a (surface CD5(+) CD45RA(low)), B-1b ( surface CD5(-), CD45RA(low), CD5 mRNA(+)), and B-2 (surface CD5(-), CD 45RA(high), CD5 mRNA(-)) cells, respectively,sorted from adult human p eripheral blood. Most B-1a and B-1b, but no B-2, cell-derived mAbs wer e polyreactive; i.e., they bound different self and foreign Ags with d ifferent affinities. B-1a and B-2 mAbs preferentially utilized V(H)4 ( p = 0.003) and V(H)3 (p = 0.010) genes, respectively. All three mAb po pulations utilized DXP, DLR, DN D-H genes, and J(H)6, but no mAb utili zed DHQ52. There were fewer unencoded nucleotide (N) additions in the VHDH, junctions of B-1b (3.00 +/- 2.52, mean +/- SD) than of B-1a (12. 45 +/- 3.93, p = 1.23 x 10(-5)) or B-2 (8.29 +/- 4.75, p = 0.020) mAbs . Partly due to the fewer N additions and a paucity of D-D fusions, th e B-1b mAb CDR3s were significantly shorter than the B-1a mAb CDR3s (p = 0.013), which contained a nonrandom Tyr distribution (p = 0.003). F inally, all but two B-1 cell-derived mAbs were mutated, in a fashion s imilar to that of the Ag-selected B-2 mAbs. Thus, in the human adult, B-1 cells that make natural polyreactive Abs may not be representative of the predominantly B-1 developmental waves of colonization of the f etal and neonatal B cell repertoires, and are somatically selected.