NUCLEOTIDE-SEQUENCE ANALYSIS OF THE V(L) AND V(H) DOMAINS OF 5 HUMAN-IGM DIRECTED TO LAMIN-B - EVIDENCE FOR AN ANTIGEN-DRIVEN PROCESS IN THE GENERATION OF HUMAN AUTOANTIBODIES TO LAMIN-B

Objective. To gain insight into the genetic origin of human antilamin autoantibodies, we determined the nucleotide sequence of the light and heavy chain variable region (V(L) and V(H)) domains of 5 IgM antibodies directed to lamin B. These antibodies represent a distinct subset of antinuclear antibodies, and their presence is associated with a particular lupus-like syndrome. Methods. We derived and cloned lymphoblastoid cell lines from peripheral blood B cells of 3 patients, selected anti-lamin B-producing subclones, and sequenced the messenger RNA coding for Ig heavy and light chains. Results. We isolated 2 subclones (1 IgMkappa, 1 IgMlambda) from one patient (FUR) and 2 subclones (both IgMlambda) from another (HER). In contrast, all 8 lines derived from B cells isolated from the third patient (BEN) synthesized identical anti-lamin B IgMkappa antibodies: All V(L) and V(H) domains from these 5 IgM were encoded by different V(L) Or V(H) genes. D(H) regions were all different, and there was no restriction in the use Of J(L) or J(H) segments. Analysis of the nucleotide sequence of the V(L) domains allowed the identification of the putative germinal gene in 3 instances (VkappaIV, Humkv325, and VlambdaIII.1); the overall ratios of replacement:silent mutations (R:S) were 6.5 and 1.2 in the complementarity determining regions (CDRs) and framework regions (FRs), respectively. The 2 other lambda sequences belonged to the VlambdaIII family. With regard to V(H) domains, 3 of 5 derived from previously identified germline genes (V(H)IV 4.19, V(H)IV 4.22, and V(H)III 9.1); the overall R:S ratio for these genes was 8 and 1.5 in CDRs and FRs, respectively. Conclusion. Taken together, these data provide evidence that the repertoire of human antilamin autoantibodies is not restricted and that the antigen (or another kind of selective pressure) plays a role in the generation of autoantibodies to lamin B. This hypothesis is in accordance with the reactivity of these antibodies to discrete epitopes of lamin B.