Immune synapses between mast cells and γδ T cells limit viral infection

Mast cells (MCs) are immune sentinels, but whether they also function as antigen-presenting cells (APCs) remains elusive. Using mouse models of MC deficiency, we report on MC-dependent recruitment and activation of multiple T cell subsets to the skin and draining lymph nodes (DLNs) during dengue virus (DENV) infection. Newly recruited and locally proliferating gamma delta T cells were the first T cell subset to respond to MC-driven inflammation, and their production of IFN-gamma was MC dependent. MC-gamma delta T cell conjugates were observed consistently in infected peripheral tissues, suggesting a new role for MCs as nonconventional APCs for gamma delta T cells. MC-dependent gamma delta T cell activation and proliferation during DENV infection required T cell receptor (TCR) signaling and the nonconventional antigen presentation molecule endothelial cell protein C receptor (EPCR) on MCs. gamma delta T cells, not previously implicated in DENV host defense, killed infected targeted DCs and contributed to the clearance of DENV in vivo. We believe immune synapse formation between MCs and gamma delta T cells is a novel mechanism to induce specific and protective immunity at sites of viral infection.