Characterisation of macaque testicular leucocyte populations and T-lymphocyte immunity

The rodent testis is well established as a site of immune privilege where both innate and acquired immune responses are suppressed. Immune cells and responses within human or non-human primate testes, by contrast, are poorly characterised. This study used multi-colour flow cytometry to characterise the leukocytes in testicular cells isolated from 12 young adult pigtail macaques (Macaca nemestrina) by collagenase dispersal, and to measure the cytokine responses of macaque testicular T-lymphocytes to mitogens. B-lymphocytes and granulocytes were present in very low numbers (0.24% and 3.3% of leukocytes respectively), indicating minimal blood contamination. A median of 30.8% of the recovered testicular leukocytes were CD3+ lymphocytes, with CD4 and CD8 T-lymphocyte proportions similar to those in the blood. The proportion of naïve T-lymphocytes in the testis was low, with significantly higher frequencies of central memory cells, compared with the blood. A median of 42.7% of the testicular leukocytes were CD163+ macrophages, while 4.5% were CD14+CD163- monocyte-like macrophages. Small populations of myeloid and plasmacytoid dendritic cells, NK cells and NKT cells were also detected. Following mitogen stimulation, 19.7% of blood T-lymphocytes produced IFNγ and/or TNF, whereas significantly fewer (4.4%) of the testicular T-lymphocytes responded to stimulation. Our results characterise the immune cells within the adult macaque testis and identify a suppression of T-lymphocyte responses. This study provides a baseline to examine the immunology of the primate testis and suggests that testicular immune privilege could also be present in primates.