TLR7 induces anergy in human CD4+ T cells

The role of TLRs in CD4 + T cells is poorly understood. Hafler and colleagues demonstrate that ligation of TLR7 initiates an anergic program in CD4 + T cells and might have implications for HIV infection. The recognition of microbial patterns by Toll-like receptors (TLRs) is critical for activation of the innate immune system. Although TLRs are expressed by human CD4 + T cells, their function is not well understood. Here we found that engagement of TLR7 in CD4 + T cells induced intracellular calcium flux with activation of an anergic gene-expression program dependent on the transcription factor NFATc2, as well as unresponsiveness of T cells. As chronic infection with RNA viruses such as human immunodeficiency virus type 1 (HIV-1) induces profound dysfunction of CD4 + T cells, we investigated the role of TLR7-induced anergy in HIV-1 infection. Silencing of TLR7 markedly decreased the frequency of HIV-1-infected CD4 + T cells and restored the responsiveness of those HIV-1 + CD4 + T cells. Our results elucidate a previously unknown function for microbial pattern–recognition receptors in the downregulation of immune responses.