Endogenous DAMPs elicited during transplantation are recognized via TLR-MyD88 and NLRP3-inflammosome pathways that are expressed in APCs including B cells. Here, we asked whether B cell intrinsic NLRP3-activation is essential for B cell mediated functions in chronic rejection.

Methods: We made bone marrow chimeras lacking NLRP3 only in B cells. Irradiated [mu]MTCD45.1/CD45.2 mice were transplanted with bone marrow cells from [mu]MTCD45.1/CD45.2 and wtCD45.2 ([mu]MT+wt) or [mu]MTCD45.1/CD45.2 and NLRP3-/-CD45.2 ([mu]MT+NLRP3-/-). NLRP3 deficiency (CD45.2+) was restricted to B cells (98±0.5%) and limited in non-B cells (15±5%). 12 weeks later, chimeras received OT1 (1 x 10⁶) and OT2 (3 x 10⁶) Thy1.1+ T cells followed by H2b/d-Ova heart transplants. Extent of chronic allograft vasculopathy (CAV) was assessed by morphometric quantitation of luminal occlusion of vessels at 70days. We examined endogenous (Thy1.1-) and transferred T cell (Thy1.1+) functions after restimulation with donor cells by FACS. B cell cytokines were analyzed after CpG DNA and donor cell stimulation.

Results: Heart allografts in [mu]MT+NLRP3-/- showed significantly diminished CAV than in [mu]MT+wt chimeras (p < 0.005, n=6–8/grp). Graft reactive IgM and IgG were preserved in [mu]MT+NLRP3-/- with similar titers to [mu]MT+wt mice. At 30days after transplantation, graft reactive endogenous CD4 and CD8 IFNγ+ T cells were significantly diminished in [mu]MT+NLRP3-/- than in [mu]MT+wt recipients (p < 0.05, n=4-5/grp) while T_REG were similar. Similarly, graft reactive IFNγ+, TNFα+ and IL2+ cells within the harvested OT1 and OT2 populations were significantly decreased in [mu]MT+NLRP3-/- than in [mu]MT+wt recipients (p < 0.005, n=4-5/grp). Also, OT1 T cells infiltrating the allografts were reduced in [mu]MT+NLRP3-/- recipients. Upon analyses of APCs, expression of MHCII, CD40, CD80 and CD86 on B cells was reduced in [mu]MT+NLRP3-/- than in [mu]MT+wt mice suggesting possibly impaired antigen presentation by B cells. However, B cell cytokine expression (IL6, IL10, IFNγ, TNFα) was largely preserved in [mu]MT+NLRP3-/- except for decreased IL12p35 (p < 0.05, n=4/grp).

Conclusions: (a) NLRP3 is not essential for B cell antibody production in response to alloantigens (b) Intrinsic NLRP3-dependent B cell functions are important for alloreactive T cell cytokine production and graft infiltration in mediating chronic rejection.

CITATION INFORMATION: Nie J., Ramaswami B., Guo X., Hoffman R., Chalasani G. Role of B Cell Intrinsic NLRP3 in the Development of Chronic Rejection Am J Transplant. 2017;17 (suppl 3).

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