a, Immunohistochemistry and quantification of GLP-1-producing L-cells in whole ileum preparations of 6 wild-type and 5 β7−/− mice. b, Small-intestinal IEL mixtures were incubated with the fluorescently (Cys40SeTau647) labelled GLP-1R agonist exendin-4 and the capacity of agonist binding by the different subsets—natural IELs (Glp1rhigh), induced IELs (Glp1rlow) and non-T cells—was analysed by flow cytometry. Sorted Glp1rhigh and Glp1rlow cells were also incubated with recombinant GLP-1 and the remaining supernatant GLP-1 was plotted against the relative Glp1r mRNA levels of the cells. c, GLP-1-producing GLUTag cells were co-cultured with sorted natural (Glp1rhigh) or induced (Glp1rlow) IELs. After 24 h, the concentration of GLP-1 in the supernatant was measured. n = 5 biologically independent samples for Glp1rhigh IELs and n = 4 biologically independent samples for Glp1rlow IELs. d, Left, GLUTag cells were co-cultured with sorted Glp1rhigh IELs in the presence of exendin-4 (100 nM) or control. n = 3 independent biologically samples per group. Right, GLUTag cells were stimulated with exendin-4 (100 nM) or control. n = 4 independent biological samples per group. After 24 h, the concentration of GLP-1 in the supernatant was measured. e, Sorted Glp1rhigh IELs were incubated with exendin-4 (100 nM) or control. After 24 h, samples were centrifuged and supernatants were transferred to ex vivo ileum fractions of wild-type mice. GLP-1 levels were determined 24 h later from ex vivo supernatants. n = 10 biologically independent mice per group. f, Whole gut preparations of wild-type or β7−/− mice were treated with or without the GLP-1 receptor antagonist exendin-9 (100 nM). After 24 h, the concentration of GLP-1 in the supernatant was measured. n = 5 biologically independent samples for wild-type or β7−/− mice without exendin-9; n = 4 biologically independent samples for wild-type mice with exendin-9. Data are mean ± s.e.m. *P < 0.05, **P < 0.01. All P values from two-tailed unpaired Student’s t-test. Source data