Development of murine lupus involves the combined genetic contribution of the SLAM and FcgammaR intervals within the Nba2 autoimmune susceptibility locus

Autoantibodies are of central importance in the pathogenesis of Ab-mediated autoimmune disorders. The murine lupus susceptibility locus Nba2 on chromosome 1 and the syntenic human locus are associated with a loss of immune tolerance that leads to antinuclear Ab production. To identify gene intervals within Nba2 that control the development of autoantibody-producing B cells and to determine the cellular components through which Nba2 genes accomplish this, we generated congenic mice expressing various Nba2 intervals where genes for the FcgammaR, SLAM, and IFN-inducible families are encoded. Analysis of congenic strains demonstrated that the FcgammaR and SLAM intervals independently controlled the severity of autoantibody production and renal disease, yet are both required for lupus susceptibility. Deregulated homeostasis of terminally differentiated B cells was found to be controlled by the FcgammaR interval where FcgammaRIIb-mediated apoptosis of germinal center B cells and plasma cells was impaired. Increased numbers of activated plasmacytoid dendritic cells that were distinctly CD19+ and promoted plasma cell differentiation via the proinflammatory cytokines IL-10 and IFNalpha were linked to the SLAM interval. These findings suggest that SLAM and FcgammaR intervals act cooperatively to influence the clinical course of disease through supporting the differentiation and survival of autoantibody-producing cells.

Separation of the New Zealand Black genetic contribution to lupus from New Zealand Black determined expansions of marginal zone B and B1a cells

The F(1) hybrid of New Zealand Black (NZB) and New Zealand White (NZW) mice develop an autoimmune disease similar to human systemic lupus erythematosus. Because NZB and (NZB x NZW)F(1) mice manifest expansions of marginal zone (MZ) B and B1a cells, it has been postulated that these B cell abnormalities are central to the NZB genetic contribution to lupus. Our previous studies have shown that a major NZB contribution comes from the Nba2 locus on chromosome 1. C57BL/6 (B6) mice congenic for Nba2 produce antinuclear Abs, and (B6.Nba2 x NZW)F(1) mice develop elevated autoantibodies and nephritis similar to (NZB x NZW)F(1) mice. We studied B cell populations of B6.Nba2 mice to better understand the mechanism by which Nba2 leads to disease. The results showed evidence of B cell activation early in life, including increased levels of serum IgM, CD69(+) B cells, and spontaneous IgM production in culture. However, B6.Nba2 compared with B6 mice had a decreased percentage of MZ B cells in spleen, and no increase of B1a cells in the spleen or peritoneum. Expansions of these B cell subsets were also absent in (B6.Nba2 x NZW)F(1) mice. Among the strains studied, B cell expression of beta(1) integrin correlated with differences in MZ B cell development. These results show that expansions of MZ B and B1a cells are not necessary for the NZB contribution to lupus and argue against a major role for these subsets in disease pathogenesis. The data also provide additional insight into how Nba2 contributes to lupus.