Figure 4.

Immune regulation in the testis. Under normal circumstances, cells in the testis (including Sertoli cells) produce immunoregulatory factors that favor the presence of regulatory immune cells, including M2 macrophages, Tregs, and tolerogenic dendritic cells, that maintain a milieu supporting germ cell survival. On the other hand, if bacteria and viruses invade the testis, to eliminate the pathogen, the testis can initiate an inflammatory response that includes activation of PRRs, production of inflammatory cytokines and antimicrobial factors, and recruitment and activation of inflammatory immune cells such as M1 macrophages and cytotoxic T cells. If this response to infection is kept in check it does not disrupt normal testicular function and the testis is able to maintains a delicate balance to promote spermatogenesis and prevent infection. However, if it gets out of control, inflammation in the testis can lead to disruption of the BTB and loss of germ cells. At the same time, if the response is not strong enough to eliminate the infection, it can lead to a sanctuary reservoir for viruses and bacteria. Solid red lines indicate inhibition and dashed green lines indicate potential (but not proven) functions.