Antibody-suppressor CD8+ T cells require CXCR5.

BACKGROUND: We previously reported the novel activity of alloprimed CD8 T cells that suppress post transplant alloantibody production. The purpose of the current study is to investigate the expression and role of CXCR5 on antibody-suppressor CD8 T cell function.

METHODS: C57BL/6 mice were transplanted with FVB/N hepatocytes. Alloprimed CD8 T cells were retrieved on day 7 from hepatocyte transplant recipients. Unsorted or flow-sorted (CXCR5CXCR3 and CXCR3CXCR5) alloprimed CD8 T cell subsets were analyzed for in vitro cytotoxicity and capacity to inhibit in vivo alloantibody production following adoptive transfer into C57BL/6 or high alloantibody-producing CD8 KO hepatocyte transplant recipients. Alloantibody titer was assessed in CD8 KO mice reconstituted with naïve CD8 T cells retrieved from C57BL/6, CXCR5 KO or CXCR3 KO mice. Antibody suppression by OVA-primed monoclonal OT-I CXCR5 or CXCR3 CD8 T cell subsets was also investigated.

RESULTS: Alloprimed CXCR5CXCR3CD8 T cells mediated in vitro cytotoxicity of alloprimed "self" B cells while CXCR3CXCR5CD8 T cells did not. Only flow-sorted alloprimed CXCR5CXCR3CD8 T cells (not flow-sorted alloprimed CXCR3CXCR5CD8 T cells) suppressed alloantibody production and enhanced graft survival when transferred into transplant recipients. Unlike CD8 T cells from wild-type or CXCR3 KO mice, CD8 T cells from CXCR5 KO mice do not develop alloantibody-suppressor function. Similarly, only flow-sorted CXCR5CXCR3 (and not CXCR3CXCR5) OVA-primed OT-I CD8 T cells mediated in vivo suppression of anti-OVA antibody production.

CONCLUSION: These data support the conclusion that expression of CXCR5 by antigen-primed CD8 T cells is critical for the function of antibody-suppressor CD8 T cells.