Immunoglobulin V sub(H)-gene usage of autoantibodies in mercuric chloride-induced membranous glomerulopathy in the rat

Brown-Norway (BN) and Dorus Zadel Black (DZB) rats develop a T-cell-dependent membranous glomerulopathy (MGP) with high proteinuria and antiglomerular basement membrane (GBM) autoreactive antibodies (Abs), upon exposure to mercuric chloride (HgCl sub(2)). Laminin is an important autoantigenic target of the anti-GBM Abs, absorbing approximately 30% of the anti-GBM reactivity. Although many anti-GBM Abs have undergone isotype switching, it is currently unclear whether affinity maturation occurs during the HgCl sub(2)-induced autoimmune response. To address this question we analysed the rearranged immunoglobulin heavy chain variable-region genes (V sub(H)DJ sub(H) regions) of 15 mAbs that were previously obtained from HgCl sub(2)-treated rats. Seven of these mAbs exhibit reactivity towards laminin. Our study showed that the V sub(H)-gene usage of antilaminin mAbs is largely restricted to the PC7183 V sub(H)-gene family (six out of seven). In addition, we demonstrated that at least three out of six laminin reactive and five out of six non-laminin-binding mAbs are encoded by germline V sub(H) genes (a total of eight out of 12 mAbs). Of the eight mAbs that are encoded by germline V sub(H) genes, seven are of a non-immunoglobulin M (IgM) isotype, indicating that isotype switching has occurred in these mAbs in the absence of somatic mutations. The mutations observed in the V sub(H) genes of the four remaining mAbs do not provide strong evidence for antigenic selection. The data support the notion that B cells in this model of MGP are not subjected to affinity maturation and probably result from polyclonal B-cell activation.