| Summary: | Summary: Mucosal-associated invariant T (MAIT) cells can be activated via either their T cell receptor (TCR), which recognizes MR1-bound pyrimidines derived from microbial riboflavin biosynthesis, or via cytokines. These two modes of activation may act in concert or independently, depending upon the stimulus. It is unknown, however, how MAIT cell responses differ with the mode of activation. Here, we define transcriptional and effector responses of human CD8+ MAIT cells to TCR and cytokine stimulation. We report that MAIT cells rapidly respond to TCR stimulation, producing multiple cytokines and chemokines, altering their cytotoxic granule content and transcription factor expression, and upregulating co-stimulatory proteins. In contrast, cytokine-mediated activation is slower and results in a more limited response. Therefore, we propose that, in infections by riboflavin-synthesizing bacteria, MAIT cells play a key early role in effecting and coordinating immune responses, while in the absence of TCR stimulation, their role is likely to differ. : Lamichhane et al. compare the response of human CD8+ mucosal-associated invariant T (MAIT) cells to T cell receptor (TCR) and cytokine stimuli, demonstrating distinct transcriptional responses. Early TCR-stimulated MAIT cells are polyfunctional and produce multiple proinflammatory cytokines and chemokines. In contrast, response to cytokine stimulation is more restricted. Keywords: mucosal-associated invariant T cells, T cell receptor, interleukin-12, interleukin-18, activation, effector functions, transcriptome, transcription factors
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