Background/Purpose: Systemic Lupus Erythematosus (SLE) is characterized by autoantibodies (autoAbs) against nucleic acid containing antigens. These antibodies form immune complexes that promote inflammation and cause organ damage. Defining B cell subsets that give rise to these autoAbs may reveal therapeutic approaches for SLE that spare responses to foreign antigens. Mice lacking the tyrosine kinase Lyn, which limits B and myeloid cell activation, develop lupus-like autoimmune disease characterized by a large increase in autoreactive plasma cells (PCs). Here we determine the contribution of T-bet+ age associated B cells (ABCs) and marginal zone (MZ) B cells, both of which have been implicated in lupus pathogenesis, to the accumulation of PCs and autoantibodies in Lyn-/- mice.

Methods: We used fate mapping with Tbx21-cre (Tbx21 encodes T-bet) and a td-tomato cre-inducible reporter to identify PCs derived from ABCs. Autoantibody secretion by reporter expressing and reporter negative PCs was measured by ELISA. To identify the role of MZ B cells, we blocked their development using a B cell specific, heterozygous mutation in Notch2, and assessed the effect on autoantibodies by ELISA. We also blocked PC differentiation via IRF4-deficiency and used flow cytometry to determine whether MZ B cells were increased.

Results: 40% of splenic PCs in Lyn-/- mice were derived from T-bet expressing cells, a significant increase compared to wt mice that was not seen in the bone marrow PC population. Reporter positive PCs produced anti-dsDNA IgM and IgG at levels equal to or greater than reporter negative PCs. Total IgM and anti-dsDNA IgM and IgG remained elevated in mb1-cre.Notch+/f.Lyn-/- mice, and MZ B cells were not increased in Lyn-/-IRF4-/- mice.

Conclusion: T-bet expressing B cells, but not MZ B cells, contribute to the autoreactive PC pool in Lyn-/- mice. Their enrichment in the spleen, but not BM, suggest an extrafollicular, rather than germinal center, pathway of activation. T-bet expressing cells were not the sole source of autoreactive PCs, however. Ongoing studies are aimed at identifying the role of other subsets such as B-1a cells.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/b-cell-subsets-contributing-to-the-autoreactive-plasma-cell-pool-in-lyn-mice/