MAIT cells kill bacteria-infected cells and suppress bacterial loads.

(A) Assessment of apoptosis of E. coli EC120S-infected HeLa cells by Casp3 activity and MAIT cell degranulation by CD107a, Gnly, and GrzB expression. (B) Apoptosis of infected HeLa cells at indicated time point (n = 9–11). (C) Measurement of early apoptosis (Casp3⁺DCM⁻) on uninfected or EC120S-infected HeLa cells, (D) degranulation by MAIT cells, and (E) bacterial counts following lysis of infected HeLa cells after 3 h of co-culture with and without MAIT cells in the presence of anti-MR1 or isotype control (n = 7–8 for EC120S-infected HeLa cells+anti-MR1, n = 24–25 for others). (F) Bacterial counts in infected HeLa cell lysates or in total lysates (cell lysates plus supernatants) after 3 h of co-culture with or without MAIT cells (n = 14). (G) MAIT cell degranulation, (H) apoptosis of EC120S-infected HeLa cells, and (I) relative bacterial loads following co-culture of EC120S-infected HeLa cells with MAIT cells derived from D0, 2, and 15 of culture (n = 4). (J) Percentage of cytolytic proteins expressed by MAIT cells from D0, 2, and 15 of culture assessed by flow cytometry (n = 3–10). (K, L) Flow cytometry analysis on frequency (K) and levels (MFI) (L) of cytolytic protein expression by PB (n = 4) and NP (n = 3) MAIT cells at various time points. (M) Representative FACS plot of apoptosis of EC120S-infected HeLa cells and MAIT cell degranulation following co-culture with PB or NP MAIT cells (n = 3). Data presented as heat map shows the mean, whereas data presented as line or bar graphs with error bars represent the mean and standard error. Box and whisker plots show median, the 10th to 90th percentile, and the interquartile range. Statistical significance was calculated using mixed-effects analysis followed by Tukey’s multiple comparison test (C–E), Wilcoxon’s signed-rank test or Friedman’s test with Dunn’s multiple comparisons test (F), or repeated-measure one-way ANOVA (G–I). ****p < 0.0001, ***p < 0.001, **p < 0.01, *p < 0.05. The underlying data of this figure can be found in S1 Data. Casp, caspase; CFU, colony-forming units; D, day; DCM, dead cell marker; FACS, fluorescence-activated cell sorting; Gnly, granulysin; GrzB, Granzyme B; MAIT, Mucosa-associated invariant T; MFI, mean fluorescence intensisty; MR1, MHC-Ib-related protein; NP, nasopharyngeal; ns, not significant; PB, peripheral blood.