Immunoglobulin VH-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 (HgCl2). Laminin is an important autoantigenic target of the anti-GBM Abs, absorbing approximate to 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 HgCl2-induced autoimmune response. To address this question we analyzed the rearranged immunoglobulin heavy chain variable-region genes (V(H)DJ(H) regions) of 15 mAbs that were previously obtained from HgCl2-treated rats. Seven of these mAbs exhibit reactivity towards laminin. Our study showed that the V-H-gene usage of antilaminin mAbs is largely restricted to the PC7183 V-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-H genes (a total of eight out of 12 mAbs). Of the eight mAbs that are encoded by germline V-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-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.