Isolation and molecular characterization of the B cells producing the paraprotein in a case of benign monoclonal gammapathy in C57BL mice

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 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 HgCl2-induced autoimmune response. To address this question we analysed the rearranged immunoglobulin heavy chain variable-region genes (VHDJH 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 VH-gene usage of antilaminin mAbs is largely restricted to the PC7183 VH-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 VH genes (a total of eight out of 12 mAbs). Of the eight mAbs that are encoded by germline VH 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 VH 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.

Immunoglobulin VH gene sequence analysis of spontaneous murine immunoglobulin-secreting B-cell tumours with clinical features of human disease

The 5T series of multiple myelomas (MM) and Waldenstrsöm's macroglobulinaemia-like lymphomas (WM), which developed spontaneously in ageing mice of the C57BL/KaLwRij strain, shows clinical and biological features that closely resemble their corresponding human diseases. In order to compare the patterns of somatic mutation in VH genes of mouse tumours with those of human counterparts, we have determined and analysed sequences of immunoglobulin VH genes in five cases of murine MM, two of WM and one of biclonal benign monoclonal gammopathy (BMG). Four of five MM and 2/2 WM cases used VH genes of the large J558 family; one MM used a gene of the VGAM3.8 family, and both clones of the BMG used genes of the 36-60 family. N-region insertions were observed in all cases, but D-segment genes were only identified in 6/9 cases, which were all from the D-SP family and translated in reading frame 3. Compared with human MM, in which the VH genes have been found to be consistently hypermutated (mean% +/- SD = 8.8 +/- 3.2), the degree of somatic mutation in the murine tumours was significantly lower (mean% +/- SD = 2.9 +/- 2.3). There was no significant evidence of clustering of replacement mutations in complementarity determining regions (CDR), a feature considered to be characteristic of antigen-selected sequences. However, one clone of the biclonal BMG case showed intraclonal variation, a feature described in some cases of human BMG. These results indicate that murine VH genes in mature tumours differ from human counterparts in the level and distribution of somatic mutations, but support the concept that BMG may be distinct from MM.