supplied critical reagents. MR1 and MR1T cells also play a significant role in bat immune defense. hybridization (Flow-FISH) technology for gene expression at the mRNA level, both CD4+ and CD8+ T?cells can be identified in pteropodid bats (Martinez Gomez et?al., 2016). In addition, subsets of B cells have been explained in pteropodid bats by employing a similar strategy of screening for suitable species cross-reactive antibodies (Periasamy et?al., 2019). Lastly, several subsets of blood monocytes and alveolar macrophages were identified using a comparable approach (Gamage et?al., 2020). The major histocompatibility complex (MHC)-Ib related protein (MR1) presents vitamin B2-related antigens (Corbett et?al., 2014; Kjer-Nielsen et?al., 2012), to a Swertiamarin group of unconventional innate-like T?cell populations expressing semi-invariant T?cell receptor (TCR) rearrangements collectively known as MR1-restricted T (MR1T) cells (Godfrey et?al., 2019; Huang et?al., 2005; Treiner et?al., 2003). MR1 displays an extraordinary level of evolutionary conservation among eutherian mammals (Huang et?al., 2009; Mondot et?al., 2016; Riegert et?al., 1998; Tsukamoto et?al., 2013), with the corresponding invariant TCR rearrangements and MR1T cell populations in eutherians where MR1 is present (Boudinot et?al., 2016; Goldfinch et?al., 2010; Rahimpour et?al., 2015; Xiao et?al., 2019). In contrast, specific lack of the corresponding invariant TCR rearrangements and MR1T cell populations are noted in some mammals where the gene for MR1 is usually absent, such as mammals belonging to the orders of Carnivora and Lagomorpha, as well as the armadillos (Xenarthra) (Boudinot et?al., 2016). Overall, these observations suggest that MR1 and MR1T cells have co-evolved under selection pressure and implicate their importance in the immune system of eutherian mammals (Boudinot et?al., 2016; Godfrey et?al., 2019; Huang et?al., 2009). In mice and humans, classical mucosal-associated invariant T (MAIT) cells expressing an invariant TCR with the TRAV1-2 segment represent the vast majority of MR1T cells (Godfrey et?al., 2019). MAIT cells identify vitamins B2 (riboflavin) and B9 (folic acid)-related microbial metabolites and are an antimicrobial T?cell populace present in high large quantity in tissues and blood circulation (Godfrey et?al., 2019). MAIT cells rapidly perform a range of effector responses following MR1-restricted acknowledgement of antigen, including cytokine production, cytotoxicity, antimicrobial activity, and tissue repair (Boulouis et?al., 2020b; Constantinides et?al., 2019; Dusseaux et?al., 2011; Gibbs et?al., 2017; Hinks et?al., 2019; Lamichhane et?al., 2019; Leeansyah et?al., 2013; Leng et?al., 2019; Meierovics et?al., 2013). MAIT cell development and functional characteristics are under the control of the grasp transcription factor promyelocytic leukemia zinc finger (PLZF, or zinc finger and BTB domain name made up of 16, ZBTB16), the Th17-associated retinoid-related orphan receptor (ROR) t, as well as the T?cell transcription factors eomesodermin (eomes) and T box transcription factor 21 (TBX21, or T-bet) (Dusseaux et?al., 2011; Koay Swertiamarin et?al., 2016, 2019; Leeansyah et?al., 2014, 2015; Martin et?al., 2009; Savage et?al., 2008). Evidence from human and challenge studies, as well as murine and non-human primate models of infectious diseases, strongly support an important role Swertiamarin of MAIT cells in various bacterial and viral infections (Boulouis et?al., 2020b; Ellis et?al., 2020; Howson et?al., 2018; Le Bourhis et?al., 2010; Meierovics et?al., 2013; Salerno-Goncalves et?al., 2017; Fzd4 van Wilgenburg et?al., 2018; Wang et?al., 2018, 2019). Interestingly, this includes Swertiamarin the recent observation that MAIT cells respond strongly to SARS-CoV-2 contamination in humans (Flament et?al., 2020; Jouan et?al., 2020; Parrot et?al., 2020). Altogether, these characteristics strongly support the notion that MR1 Swertiamarin and MR1T cells perform crucial functions in the immune system of placental mammals. In the current study, we investigated the phenotypic and functional characteristics of MR1T cells in a model pteropodid bat, the fruit-eating black flying fox (Pa) belonging to the suborder Yinpterochiroptera. We provide here the first evidence of a highly abundant MR1T cell populace with MAIT cell-like characteristics in the pteropodid bats, including reactivity, proliferation, cytokine production, and cytotoxicity in response to activation by an agonist MR1-binding ligand and the model microbe and 1B). In contrast, pre-blocking with titrated hMR1-5-OP-RU tetramer completely abolished hMR1-6-FP binding at the highest hMR1-5-OP-RU tetramer concentration (Physique?1A, and 1B). These results indicate that this poor binding of Pa CD3+ T?cells to 6-FP-loaded hMR1 tetramer was of low-affinity, whereas the strong binding to 5-OP-RU-loaded hMR1 tetramer was highly specific. Open in a separate window Physique?1 MR1T Cells Are Present in Blood circulation and Tissues of MR1T cells expressed low levels of the pore-forming protein perforin (Prf), although significantly more than Pa non-MR1T cells (Figures 1E, 1F, and S2F). This is reminiscent of hMAIT cell Prf expression (Kurioka et?al.,.