Circulating Mucosal‐Associated Invariant T Cells Are Associated With Acute Human Ischemic Stroke and Predict Poor Outcome

Mucosal-associated invariant T (MAIT) cells are involved in acute ischemic stroke in mice models. This study aimed to clarify the dynamics and role of circulating MAIT cells in patients with acute ischemic stroke. Patients with acute ischemic stroke were classified according to the National Institutes of Health Stroke Scale into severe (score ≥ 10) and mild (score < 10) groups; outpatients with matched sex and age were selected as controls. Circulating MAIT cells, activation (CD69+), and cytokine production (IFN-γ [interferon-gamma] + and IL-17 [interleukin-17]+) on days 3, 10, and 17 after stroke, along with invariant natural killer T cells, gamma delta T cells, CD4+, and CD8+ T-cell populations, were analyzed by flow cytometry. The relationship between MAIT cell dynamics and clinical outcomes was examined. One hundred participants (30 severe, 40 mild, 30 controls) were included. On day 3, patients with severe stroke had a significantly lower proportion of MAIT cells than the mild group and controls (severe, mild, control [median]: 0.09%, 0.33%, 0.38%, respectively; P < 0.001), which gradually recovered on day 17. Severe stroke MAIT cells showed higher frequencies of CD69 expression and IL-17 production. Multivariate analysis showed patients in the lowest MAIT cell population quartile on day 3 had a significantly higher probability of poor outcomes at 3 months than those in the highest quartile (odds ratio, 21.64 [95% CI, 1.41-331.58]; P = 0.027). An early decrease in MAIT cells with higher activity and proinflammatory cytokine production correlated with stroke severity and poor outcomes, suggesting a significant role of MAIT cells in acute cerebral infarction and unfavorable outcomes.