Fig. 2

Here we compare the human TCRαβ⁺CD8αβ⁺ IEL subset with the TCRαβ⁺CD8αβ⁺ and TCRαβ⁺CD8αα⁺ IEL subsets found in mouse for NK receptor expression and cytokine producing capacity. a The human TCRαβ⁺CD8αβ⁺ IEL expresses NK receptors such as the activating NKG2D and inhibitory NKG2A/CD94 in the steady state, whereas the TCRαβ⁺CD8αα⁺ IEL and not the TCRαβ⁺CD8αβ⁺ IEL subset is enriched for NK receptor expression in mouse. These TCRαβ⁺CD8αα⁺ IEL express NK receptors that can be found in steady-state human IEL such as NKG2D in addition to receptors such as those of the Ly49 family and NKG2C/CD94 which can associate with the ITAM adapter molecule DAP12. Interestingly, human IEL can also gain expression of ITAM bearing NK receptors such as NKG2C/CD94 in patients with CeD. The propensity for autoreactivity of IEL TCRs is shown with more autoreactive TCRs, such as those attributed to the development of TCRαβ⁺CD8αα⁺ IEL, illustrated in red and less autoreactive TCRs illustrated in green. The threshold for TCR/non-cognate antigen interactions to result in activation can be met in the case of human TCRαβ⁺CD8αβ⁺ IEL in CeD via the costimulatory impact of inflammatory signals such as IL-15 and the engagement of activating NK receptors. b Freshly isolated IEL were treated with 50 ng/mL of PMA and 500 ng/mL of Ionomycin for 3 h to assess the expression of Granzyme B and IFN-γ at steady state for human TCRαβ⁺CD8αβ⁺ IEL from a 30-year-old individual and TCRαβ⁺CD8αβ⁺ and TCRαβ⁺CD8αα⁺ IEL from 4-week and 11-week-old C57BL/6 SPF mice, revealing human TCRαβ⁺CD8αβ⁺ IEL are potent cytokine producers and simultaneously express Granzyme B, while cytokine production is age dependent and exclusive to the mouse TCRαβ⁺CD8αβ⁺ IEL with TCRαβ⁺CD8αα⁺ IEL being more potent expressers of Granzyme B. Representative flow cytometry contour plots with outliers and large dots are shown for intracellular staining with fluorescently labeled antibody against IFN-γ and Granzyme B for human (left) and mouse (right)