MOLECULAR ANALYSIS OF SPONTANEOUS NEPHROTROPIC ANTI-LAMININ ANTIBODIES IN AN AUTOIMMUNE MRL-IPR IPR MOUSE

To explore the genetic relationship between anti-laminin and anti-DNA autoantibodies (autoAb), V(H) gene and gene family expression were det ermined among autoAb derived from an individual 6-mo-old MRL-lpr/lpr m ouse. Whereas 85% of the anti-DNA Ig were identified by one of two V(H ) family probes, 7183 and V(H)J558, none of the anti-laminin antibodie s (Ab) examined were recognized by these probes. Subsequent V region s equence analysis of three of the anti-laminin Ab revealed that they in fact utilized a J558 V(H) gene (V(H)50). Furthermore, FR2 and CDR2 ol igonucleotide probes complementary to V(H)50 recognized multiple anti- laminin Ab by Northern blot analysis; the FR2 probe recognized two con trol anti-DNA Ab, but neither probe recognized anti-DNA Ab from the sa me mouse. Polymerase chain reaction amplification of MRL-lpr/lpr genom ic liver DNA using primers generated from V(H)50 and V(k)50 sequences indicated that all three anti-laminin Ig have a single replacement mut ation in both their V(H) and V(k) genes. Search of the nucleic acid da tabases revealed that both germline V(H) and V(k) genes are expressed unmutated by murine lupus anti-dsDNA autoAb, previously sequenced in o ther laboratories. Sequence comparisons suggest that differences in an ti-DNA and anti-laminin reactivity may be dependent upon somatically g enerated differences in the CDR3 regions of the H and L chains. The re sults indicate that lupus anti-laminin Ab can arise from distinct B ce ll populations but express the same unmutated germline V region genes as lupus anti-dsDNA autoAb. They further raise the possibility that th ese distinct B cell populations may be activated and expanded either: independently, by distinct Ig receptor ligands such as the Ag, laminin and DNA; or simultaneously, by a common ligand such as an anti-Id rec ognizing a common V region epitope.