A novel population of myeloid Gr-1+ cells expressing FasL and perforin mediate contact hypersensitivity responses in skin (CAM5P.236)

Allergic contact hypersensitivity (CHS) is a CD8 T cell mediated response to hapten sensitization and challenge of the skin. Hapten-primed CD8 cell infiltration into the skin challenge site requires prior Gr-1+ cell infiltration into the site. Despite WT levels of CD8 priming, sensitized gld/perforin-/- mice have no CHS to hapten challenge. The response is restored in these mice by transfer of WT bone marrow derived Gr-1+ cells at the time of hapten challenge. The goal of this study was to further characterize these Gr-1+ cells. Gr-1+cells were purified from the bone marrow of sensitized and challenged mice by depletion of CD3+, B220+, NK1+, F4/80+, and Ly6G+ cells. qRT-PCR and Western Blot analyses confirm expression of FasL and perforin by the negatively selected cells that are 90% Gr-1+CXCR2+. Flow cytometry analyses indicate the FasL+ cells within this population express CD11c, CXCR2, CCR2, Ly6C, and CX3CR1. These Gr-1+cells, but not neutrophils, induce apoptosis of cultured endothelial cells. Transfer of these Gr-1+ myeloid cells to sensitized gld/perforin-/- mice during hapten challenge induces expression of the T cell chemoattractants CCL1, CCL2, and CCL5 in the challenged skin. These results describe a novel population of bone marrow derived Gr-1+CXCR2+ myeloid cells expressing FasL and perforin that induce expression of the chemoattractants required to direct hapten-primed T cell infiltration into the challenged skin site to mediate CHS.