High-frequency representation of a single V_H gene in the expressed human B cell repertoire

Idiotype (Id) 16/6 marks a variable (V) region structure that occurs frequently in the human immunoglobulin repertoire. The basis of the Id has been traced to a germline heavy chain gene segment, V_H18/2 (V_H26). To pursue the molecular basis for the frequency of Id 16/6, we have analyzed polymerase chain reaction-generated Cμ, Cγ, and V_H3 family V gene libraries derived from the circulating and tonsillar B cells of four normal individuals and from the B cells of two patients with active systemic lupus erythematosus (SLE). The frequency of V_H18/2 in these libraries was compared with three control V_H genes, V_H56P1, V_H21/28, and V_HA57. Plaque lifts from Cμ and Cγ V_H cDNA libraries were screened with gene-specific oligonucleotide probes. The frequency of V_H18/2 ranged from 4 to 10% of J_H⁺ plaques (two to five times that of control V_H genes). In four V_H3 family-specific libraries derived from rearranged DNA, V_H18/2 represented 19-33% of V_H3⁺ plaques. Hybridizing V_H18/2 plaques were 98-100% homologous to the germline V_H gene; mutations when present were often in framework 3. Extensive variation was seen in the complementarity determining region 3 sequences of these rearranged V genes. The high frequency of V_H18/2 expression in the B cell repertoire was confirmed by sequencing randomly picked J_H⁺ plaques. In two patients with active SLE the frequency of use of V_H18/2 was not greater than that observed in normal subjects. These results show that V_H18/2 is overrepresented in the B cell repertoire of normal subjects and suggest that the immune repertoire may be dominated by relatively few V genes.