The MAIT TCRβ chain contributes to discrimination of microbial ligand

Mucosal-associated invariant T (MAIT) cells are key players in the immune response against microbial infection. The MAIT T-cell receptor (TCR) recognizes a diverse array of microbial ligands, and recent reports have highlighted the variability in the MAIT TCR that could further contribute to discrimination of ligand. The MAIT TCR complementarity determining region (CDR)3β sequence displays a high level of diversity across individuals, and clonotype usage appears to be dependent on antigenic exposure. To address the relationship between the MAIT TCR and microbial ligand, we utilized a previously defined panel of MAIT cell clones that demonstrated variability in responses against different microbial infections. Sequencing of these clones revealed four pairs, each with shared (identical) CDR3α and different CDR3β sequences. These pairs demonstrated varied responses against microbially infected dendritic cells as well as against 5-(2-oxopropylideneamino)-6-d-ribitylaminouracil, a ligand abundant in Salmonella enterica serovar Typhimurium, suggesting that the CDR3β contributes to differences in ligand discrimination. Taken together, these results highlight a key role for the MAIT CDR3β region in distinguishing between MR1-bound antigens and ligands.