Immunoglobulin V-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-depende nt membranous glomerulopathy (MGP) with high proteinuria and antiglomerular basement membrane (GBM) autoreactive antibodies (Abs), upon exposure to me rcuric chloride (HgCl2). Laminin is an important autoantigenic target of th e anti-GBM Abs, absorbing approximate to 30% of the anti-GBM reactivity. Al though many anti-GBM Abs have undergone isotype switching, it is currently unclear whether affinity maturation occurs during the HgCl2-induced autoimm une response. To address this question we analyzed the rearranged immunoglo bulin 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 exhi bit 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 b y germline V-H genes (a total of eight out of 12 mAbs). Of the eight mAbs t hat 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 gen es 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 ar e not subjected to affinity maturation and probably result from polyclonal B-cell activation.