Background:

Alloreactive memory T cells mediate accelerated rejection of allografts and prevent tolerance induction. While regulatory B cells (Bregs) can promote tolerance induction through suppression of naïve T cell activation, their ability to suppress memory T cell responses is unknown. In this study, we tested whether TIM-1+ B cells can suppress IFN-y production of alloreactive memory T cells activated in vitro through direct allorecognition.

Methods:

B cells were purified from BALB/c (H2Kd) mouse splenocytes and co-cultured with CD40L transfected NIH/3T3 feeder cell line at a 1:1 ratio in the presence of BAFF and IL-4 for the first 4 days, followed by BAFF and IL-21 for the last 96 hours. CD19+ TIM1+ or TIM1- cells were FACS-sorted.

Next, BALB/c mice were primed with a fully mismatched skin graft from a C57BL/6 (H2Kb) mouse. Unmanipulated and syngeneic grafted mice were used as controls. Splenocytes were harvested at day 60. The frequency of memory T cells producing IFN-y was measured by ELISPOT after 48 hours stimulation with donor irradiated splenocytes with or without TIM1+ or TIM1- B cells (1:1 ratio).

Results:

We observed a 56% reduction of the frequency of activated memory T cells producing IFN-y, and 80.7% reduction of the response by T cells from naïve mice in the presence of TIM-1+ B cells, while TIM-1- B cells had no effects. In addition, the average size of the IFN-y spots (which reflects the quantity of cytokine produced per cell) was significantly smaller (p<0.0001) when TIM1+, but not TIM1-, B cells were cultured with alloreactive memory T cells.

Conclusion:

CD19+ TIM1+ regulatory B cells can inhibit the expansion and inflammatory cytokine release of memory T cells activated in vitro through direct allorecognition.

CITATION INFORMATION: Gonzalez-Nolasco B, Tector H, Markmann J, Benichou G. Inhibition of Memory T Cell Alloresponses by TIM-1+ B Cells. Am J Transplant. 2017;17 (suppl 3).

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