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 antibodi es directed to lamin B. These antibodies represent a distinct subset o f antinuclear antibodies, and their presence is associated with a part icular lupus-like syndrome. Methods. We derived and cloned lymphoblast oid cell lines from peripheral blood B cells of 3 patients, selected a nti-lamin B-producing subclones, and sequenced the messenger RNA codin g for Ig heavy and light chains. Results. We isolated 2 subclones (1 I gMkappa, 1 IgMlambda) from one patient (FUR) and 2 subclones (both IgM lambda) from another (HER). In contrast, all 8 lines derived from B ce lls isolated from the third patient (BEN) synthesized identical anti-l amin 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 d ifferent, and there was no restriction in the use Of J(L) or J(H) segm ents. Analysis of the nucleotide sequence of the V(L) domains allowed the identification of the putative germinal gene in 3 instances (Vkapp aIV, Humkv325, and VlambdaIII.1); the overall ratios of replacement:si lent mutations (R:S) were 6.5 and 1.2 in the complementarity determini ng regions (CDRs) and framework regions (FRs), respectively. The 2 oth er 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 fo r these genes was 8 and 1.5 in CDRs and FRs, respectively. Conclusion. Taken together, these data provide evidence that the repertoire of hu man antilamin autoantibodies is not restricted and that the antigen (o r another kind of selective pressure) plays a role in the generation o f autoantibodies to lamin B. This hypothesis is in accordance with the reactivity of these antibodies to discrete epitopes of lamin B.