Epithelial membrane protein 3 (Emp3) downregulates induction and function of cytotoxic T lymphocytes by macrophages via TNF-α production

Tetraspanin membrane protein, epithelial membrane protein 3 (Emp3), is expressed in lymphoid tissues. Herein, we have examined the Emp3 in antigen presenting cell (APC) function in the CD8⁺ cytotoxic T lymphocytes (CTLs) induction. Emp3-overexpressing RAW264.7 macrophage cell line derived from BALB/c mice reduced anti-C57BL/6 alloreactive CTL induction, while Emp3-knockdown RAW264.7 enhanced it compared with parent RAW267.4. Emp3-overexpressing RAW264.7 inhibited, but Emp3-knockdown RAW264.7 augmented, CD8⁺ T cell proliferation, interferon-γ secretion, IL-2 consumption, and IL-2Rα expression on CD8⁺ T cells. The supernatant from co-culture with Emp3-overexpressing RAW264.7 contained higher amount of TNF-α, and TNF- α neutralization significantly restored all these inhibitions and the alloreactive CTL induction. These results suggest that Emp3 in allogeneic APCs possesses the inhibitory function of alloreactive CTL induction by downregulation of IL-2Rα expression CD8⁺ T cells via an increase in TNF-α production. This demonstrates a novel mechanism for regulating CTL induction by Emp3 in APCs through TNF-α production.