A natural autoantibody is encoded by germline heavy and lambda light chain variable region genes without somatic mutation.

While nonmutated germline variable region (V) genes have been found to encode heavy or light chains of various human autoantibodies, the use of germline V genes by both chains of a given autoantibody has not been documented. Recently, we reported that the heavy chain V gene (designated Humha346) of the Kim4.6 anti-DNA antibody is identical to a germline VH gene, 1.9III. To investigate whether this autoantibody was entirely germline encoded, we searched for the germline counterpart to the Kim4.6 V lambda segment (designated Humla146) and isolated a V lambda I gene designated Humlv117, which was identical to Humla146. Together with the sequence identity of the Kim4.6/Humha346 and 1.9III VH genes, the current data provide the first direct proof that an autoantibody can be encoded entirely by germline V genes without any somatic change. In addition, Humlv117 is the first V lambda I germline gene that has been isolated, and is highly homologous to the V lambda genes expressed in two lymphomas. Thus, this V lambda I gene should provide a useful tool for investigating the expression of the human V lambda gene repertoire, particularly with regard to autoimmune and/or lymphoproliferative diseases.