Activation and functional modification of mucosal-associated invariant T cells in patients with intracranial infection following craniotomy

•To the best of our knowledge, this is the first study to investigate the level and function of MAIT cells in the CSF of patients with intracranial infections, an essential component in inflammatory development.•Our results show for the first time an abundance of MAIT cells in the cerebrospinal fluid compared to the blood of patients with intracranial infections. Notably, a higher proportion of IL-17 + MAIT cells was observed in the cerebrospinal fluid of these patients. Furthermore, CD25 and Tim-3 markers were significantly upregulated in cerebrospinal fluid MAIT cells.•Our results demonstrate that the potential role of MAIT cells in the pathogenesis of intracranial infections and that MAIT cells can be a therapeutic target of intracranial infections. Intracranial infections are among the most common complications of neurosurgery, with their incidence remaining high despite advancements in current neurosurgical techniques and aseptic technology. While the role of mucosal-associated invariant T (MAIT) cells, a subset of innate-like T lymphocytes, in bacterial defense is well-established, their involvement in intracranial infections remains unclear. In this study, we utilized flow cytometry to assess the phenotype and function of circulating and CSF MAIT cells. Our findings revealed that MAIT cells were higher in the CSF compared to blood. Notably, a higher percentage of IL-17A + MAIT cells was detected in the CSF of patients with intracranial infections. Moreover, markers indicating activation and exhaustion were significantly upregulated in CSF MAIT cells. Furthermore, elevated levels of pro-inflammatory cytokines, including IL-1β, IL-12, and IL-18, were detected in the CSF supernatants. We hypothesized that the elevated levels of IL-1β, IL-12, and IL-18 in the inflammatory milieu synergistically activate MAIT cells in the CSF. In particular, CD25 and Tim-3 expression of MAIT cells was increased by stimulation with IL-1β, IL-12, and IL-18 or CSF supernatants of intracranial infection patients. Collectively, these findings provide important information underlying the innate immune response of patients with intracranial infections.