Regulatory CD8+ T cells suppress disease

Description A subset of CD8+ T cells regulate chronic inflammation by killing pathogenic CD4+ T cells In vertebrates, precise orchestration of immune responses largely relies on two major subsets of T lymphocytes. CD8+ T cells are cytotoxic and can eliminate virus-infected host cells, whereas CD4+ T cells provide signals that help the activation of CD8+ T cells and antibody production by B lymphocytes. To avoid hyperactivation that may lead to irreparable tissue damage but also to prevent inadvertent responses against host tissues, a complex set of regulatory mechanisms exist. CD4+ regulatory T cells (Tregs) have been well characterized (1). By contrast, the existence of regulatory CD8+ T cells is a matter of debate. In mice, regulatory CD8+ T cells elicited in a model of multiple sclerosis reduced disease severity by suppressing autoimmune CD4+ T cells (2). On page 265 of this issue, Li et al. (3) provide evidence that a subset of human CD8+ T cells also selectively suppress pathogenic CD4+ T cells during autoimmune or infectious diseases, including flu and COVID-19.