Toll-like receptor 4 signaling in T cells promotes autoimmune inflammation

Toll-like receptors (TLRs) are critical components of innate immunity and function as rapid pathogen sensors. TLR4 is expressed on CD4 ⁺ T cells as well, the functional significance of which is unclear. In this study, we analyzed the function of TLR4 in T cells but did not find a role in promoting T helper (Th) cell polarization. Instead, TLR4 ligation enhanced both CD4 ⁺ T-cell proliferation and survival in vitro. Using the experimental autoimmune encephalomyelitis (EAE) model, we found that the loss of TLR4 solely in CD4 ⁺ T cells almost completely abrogated disease symptoms, mainly through blunted Th17 and, to a lesser degree, Th1 responses. Moreover, Tlr4 ⁻/⁻ γδ T cells were defective in IL-17 and IFN-γ production following EAE induction. This study supports an important role of this innate receptor in the direct regulation of T-cell activation and survival during autoimmune inflammation.