Growing evidence suggests that recombinatorial events prior to antigen contact can generate pathogenic autoantibodies in the nonautoimmune individual, thus providing potential disease mediators if conditions arise that permit bypass of tolerance and activation of autoreactive lymphocytes. To examine the disease potential of selected germline antibody genes, Ig were created de novo by in vitro recombination of Ig H and L chains. H chain loss variant (i.e., L-chain only) cell lines were transfected with a DNA construct encoding the variable region and regulatory sequences (LamH) of a nephrotropic murine lupus anti-laminin Ig, and the resultant Ig were examined for in vitro antigen reactivity and in vivo glomerular immune deposition. The results indicate that two light chains, LamL (Vk8, Jk5) and 238L (Vk4, Jk5), expressing unrelated germline V¹ genes, combine with LamH to generate Ig that bind basement membrane laminin in vitro, diverge in their capacity to bind ssDNA, and produce two distinct patterns of glomerular immune deposits in vivo: dense mesangial matrix (LamH/LamL) and dramatic linear glomerular basement membrane (LamH/238L) deposits. The Ig genes used by both LamH and 238L are present in nonautoimmune mice as well as in lupus-prone strains. We conclude that certain unmutated Ig genes can contribute to multiple distinct disease associated specificities, including binding to intrinsic kidney antigens, and that mutation is not essential to generate these Ig. Collectively, these observations suggest that pathogenic autoantibodies can be generated in the normal preimmune repertoire by random recombinatorial and somatic events in the absence of mutation.