a Two-photon microscopy of the testis of adult TcrdH2BeGFP mice demonstrating γδ T cells (green) and collagen structures (white–grey). Using IMARIS software, motile γδ T cells were tracked (cyan lines). Scale bar represents 70 μM (n = 6 movies). b Representative immunofluorescence staining of cross sections from the testis of adult TcrdH2BeGFP mice against CD3 (red) and DAPI (white) for nuclear visualisation. Scale bars represent 50 μM (n = 4). c Representative histogram of germ cells in a WT mouse. Plot shows frequencies of germ cells of WT, Tcrδ−/− and Il17−/− mice (n = 3–5, one to two independent experiments). d Representative microphotographs of the testis of WT and Il17−/− mice. Organs are alike in aspect, proportion and volume, with similar contribution of seminiferous tubules (white arrowhead), Leydig cells in the stromal compartment (black arrowhead) and with numerous spermatozoa in the lumen of the epididymis (asterisk). Haematoxylin and eosin staining. Original magnification ×1.25 (top column, bar, 2 mm) and ×20 (middle and lower columns, bar, 100 µm) (n = 3). e Scatter plot displays ng of testosterone/mg of protein in Tcrδ−/− and Il17−/− mice compared with the respective littermate controls (n = 16–25, four independent experiments). Data represented as mean ± SD.