Reduction in mucosal‐associated invariant T cells (MAIT) in APECED patients is associated with elevated serum IFN‐γ concentration

Mucosal‐associated invariant T cells (MAIT) are innate‐like lymphocytes enriched in mucosal organs where they contribute to antimicrobial defense. APECED is an inborn error of immunity characterized by immune dysregulation and chronic mucocutaneous candidiasis. Reduction in the frequency of circulating MAITs has been reported in many inborn errors of immunity, but only in a few of them, the functional competence of MAITs has been assessed. Here, we show in a cohort of 24 patients with APECED, that the proportion of circulating MAITs was reduced compared with healthy age and sex‐matched controls (1.1% vs. 2.6% of CD3+ T cells; p < 0.001) and the MAIT cell immunophenotype was more activated. Functionally the IFN‐γ secretion of patient MAITs after stimulation was comparable to healthy controls. We observed in the patients elevated serum IFN‐γ (46.0 vs. 21.1 pg/mL; p = 0.01) and IL‐18 (42.6 vs. 13.7 pg/mL; p < 0.001) concentrations. Lower MAIT proportion did not associate with the levels of neutralizing anti‐IL‐22 or anti‐IL‐12/23 antibodies but had a clear negative correlation with serum concentrations of IFN‐γ, IL‐18, and protein C‐reactive protein. Our data suggest that reduction of circulating MAITs in patients with APECED correlates with chronic type 1 inflammation but the remaining MAITs are functionally competent.