NLRP6 Regulates CD4 Mediated Graft-Versus-Host Disease in Experimental Murine BMT

Abstract

NLRP6 (NOD-like receptor family pyrin domain containing 6) is an important inflammasome component and is highly expressed in intestinal epithelial and immune cells. NLRP6 mediated inflammasome activation plays a critical role in response to intestinal infection and preventing dysbiosis of gut microbiota. However, we recently found that NLRP6 plays a pathogenic role in GVHD. Interestingly, we also found that activated T cells increased NLRP6 expression, but the T cell autonomous role of NLRP6 in regulating T cell responses is unknown. Because NLRP6 is an important regulator of GVH responses, we tested the hypothesis that NLRP6 deficiency in donor T cells would ameliorate GVHD. To test our hypothesis, we first performed a detailed phenotypic analysis of various T cell subsets and activation markers in naive NLRP6−/− and wild-type (WT) B6 animals and found a similar distribution of naive, memory, effector and regulatory T cells. In order to examine whether the absence of NLRP6 in donors affects GVHD, WT-BALB/c animals were lethally irradiated and transplanted on day 0 with 5 × 106 bone marrow and 1.0 × 106 splenic CD90+T cells from either syngeneic WT-BALB/c, allogeneic MHC-mismatched WT-B6 or NLRP6−/− animals. Contrary to our hypothesis, the recipients receiving donor T cells from NLRP6−/− animals showed a significantly worse survival compared to allogeneic WT-B6 animals (p We hypothesized that GVHD severity and mortality was similar in the B6 into C3H.sw model because NLRP6 regulates CD4+ and CD8+ T cell responses, differently. In order to test this, we transplanted C3H.sw recipients as above except we infused either 1 × 106 CD4+ or CD8+ T cells from B6-WT or NLRP6−/− animals. GVHD severity and mortality (P To explore how NLRP6 effects T cell responses independent of inflammasome activation, we tested naive T cell proliferation in vitro after allogeneic or non-specific TCR stimulation by anti-CD3 and CD28 antibody and found that NLRP6−/− CD4+ but not CD8+ T cells proliferated more than WT-B6 CD4+ or CD8+ T cells, respectively, following either stimulus. In addition, activated NLRP6−/− CD4+ T cells showed less apoptosis than WT. Absence of NLRP6 in T cells promotes naive CD4 T cells into Th1 cell differentiation. These data suggest that NLRP6 regulates CD4+ T cell mediated immune responses and that NLRP6 in donor T cells is critical for controlling CD4+ T cell mediated GVHD.