Background/Purpose:  Anergic autoreactive B cells are thought to play a critical role in systemic lupus erythematosus (SLE), a chronic autoimmune disease where breach of tolerance to nuclear antigen leads to the production of pathogenic anti-nuclear autoantibodies (ANA). There is evidence that anergic B cells survive longer and are less tolerized in SLE patients and lupus-prone mice; however, their exact contribution to SLE pathogenesis remains unclear. Our laboratory has used congenic derivatives of the lupus-prone New Zealand Black mouse to parse the B and T cell defects involved in SLE, uncovering a B cell defect required for ANA production (in the 170.8-181 Mb interval on chromosome 1 [C1d]) as well as T cell defects (in the 124-181 Mb interval [C1b-d]) that exacerbate disease. Since these defects were sufficient to breach B cell anergy to the neo-self antigen hen egg lysozyme, we hypothesized that a similar breach would occur in the Vκ8/3H9 model of anergy, a better analogue for human SLE.

Methods:  The 3H9 heavy chain and Vκ8 light chain were knocked into their correct loci in the C1d and C1b-d strains to generate mice with homogeneous, ssDNA-specific, anergic B cell repertoires. ANAs in female 8 month old non-autoimmune (B6), C1d and C1b-d wild type (WT) and double knock-in (dKI) mice were measured by ELISA, while splenic B and T cells were examined using flow cytometry. Adoptive transfer of B6 or C1d dKI B cells into B6 or C1d WT recipients was conducted to assess the effect of the anergic milieu on B cell activity; recipients were sacrificed after 7 days and splenocytes analyzed via flow cytometry.

Results:  C1b-d WT mice had significantly increased anti-ssDNA IgG and IgM, and higher proportions of germinal centre (GC) B cells, CD86⁺ B cells and T follicular helper (T_FH) cells than B6 WT mice, with C1d WT mice also trending to significance. Surprisingly, the autoimmune B cell phenotype was attenuated in both C1 dKI strains, such that C1 dKI mice were equivalent to B6 counterparts. While the levels of T_FH cells remained significantly higher in C1 dKI mice than in B6, they were significantly decreased compared to C1 WT mice, suggesting that the attenuated breach of B cell tolerance could result from insufficient T cell priming. This explanation was supported by the observation that anergic C1d dKI B cells adoptively transferred into C1d WT mice showed similar trends to increased GC and CD86⁺ B cells as in C1d WT mice. Finally, while the proportion of T_FH cells was significantly decreased in C1b-d dKI mice compared to their WT counterparts, the proportion of T follicular regulatory (T_FR) cells remained similar to WT levels, suggesting that selective survival or induction of T_FR cells in the dKI congenic strains may play a role in their decreased autoimmune phenotype.

Conclusion:  Our results demonstrate that while the B and T cell defects in New Zealand Black congenic mice generate autoimmunity in an unconstrained immune system, these defects are not sufficient to robustly breach tolerance to endogenous nuclear antigen when the B cell repertoire is predominantly anergic, possibly due to modulation of T cell activation or regulatory cell fate.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/anergic-b-cells-may-preserve-peripheral-tolerance-in-lupus-prone-congenic-mice/