B cells can either augment or inhibit immune responses due to the presence both regulatory (Bregs) and effector (Beff) B cells expressing anti- or pro- inflammatory cytokines, respectively. The phenotype of Beff and spectrum of their cytokine repertoire is unknown, limiting understanding. We found that TIM-4 is expressed on a subset of B cells enriched for both IFNg and IL17 expression. Adoptive transfer of TIM-4⁺ Beff from alloimmunized B6 mice into B cell-deficient uMT (B6) recipients augments Th1 and Th17 responses and accelerates rejection of Balb/c (Bc) islets vs. control recipients without B cell transfer (MST 11 vs. 15d; p<0.05). In contrast, TIM-4⁺ B cells from IFNg^-/- mice do not accelerate rejection, indicating that IFNg contributes to Beff function. Surprisingly, transfer of IL17^-/- TIM-4⁺ B cells induced long-term GS in >85% of mMT recipients of Bc islets, suggesting that in the absence of IL17, these B cells exhibit potent regulatory activity. Moreover, mixed bone marrow chimera “B-IL-17^−/−”mice specifically lacking IL17 in B cells, exhibit markedly prolonged GS (MST 45d; 33% long-term GS) compared to control “B-WT” chimeras (MST 20d; p<0.05). Because IL-17 is not yet floxed, we examined RORgt, a transcription factor essential for Th17 differentiation. RORγt was also found to be essential for B cell IL17 expression. RORγtfl/fl [times]hCD20Tam-Cre mice were treated with Tamoxifen to specifically delete B cell RORgt and IL17 expression. Similar to B-IL17^−/− mice, 35% of these “B-RORgt^−/−“ mice had 35% long-term GS (Bc islets) whereas all TAM-treated Cre- controls rejected by 30d (p<0.05). Thus, B cell IL17 is an important mediator of the alloimmune response.

To specifically address the role of B cell IL17 in the T cell allo-response, CFSE-labeled OTII CD4 cells were adoptively transferred into B-IL17^−/− vs. B-WT chimeric mice immunized with allogeneic cells expressing act-mOVA. OTII cells in B-IL17^−/− vs. B-WT hosts, exhibit a 50% ↓ in proliferation, a 250% ↓ inIFNg and IL17 and 80-100%↑ in IL-4 and IL-10 (p<0.05 for all). Collectively, our data indicate that B cell IFNg, and particularly IL17, play a critical role in priming proinflammatory Teff responses that lead to rejection. Targeting TIM-4+ B cells and/or B cell IL17 may reduce rejection and unleash potent Breg activity.

CITATION INFORMATION: Ding Q, Mohib K, Rothstein D. TIM-4 Identifies Pro-Inflammatory B Effector Cells That Are Potent Drivers of Alloimmunity and Allograft Rejection Through Expression of Both IFN-γ and IL-17. Am J Transplant. 2017;17 (suppl 3).

« Back to 2017 American Transplant Congress