Innate Immune Defense Mechanisms In Mouse Male Germ Cells

Background and Objectives:The mammalian testis is an immunoprivileged organ, where allo-and auto-antigens can be tolerated by systemic immunity. Microbial pathogens, including bacteria, fungi, viruses, and parasites, may infect the testis. To overcome the immune privilege and elicit an appropriate local response against invading microbes, local testicular cells have acquired effective innate immune function. However, the innate immune function of the germ cells, majority of the testicular cells, has not been intensively investigated. This thesis focused on the pattern recognition receptor (PRR)-initiated innate immune response in mouse male germ cells.Materials and Methods:Primary mouse germ cells were isolated for in vitro study. Real-time quantitative RT-PCR was used to examine gene expression at mRNA levels. Immunohistochemistry, Western blotting, and ELISA, were used for the analysis of protein distribution and quantification. The innate immune response in vivo was investigated after injection of pathogens into the testis.Results:Several PRRs were expressed in different stages of germ cells. Toll-like receptor (TLR)11and melanoma differentiation-associated protein5(MDA5) were expressed in round and elongating spermatids. TLR3was expressed in spermatogonia and spermatocytes. TLR11can be activated by T. gondii profilin and uropathogenic E. coli (UPEC), and initiate innate immune response. Profilin induced the expression of monocyte chemotactic protein1(MCP-1), interleukin12(IL-12) and interferon gamma (IFN-y) through the activation of nuclear factor κB (NF-κB). UPEC induced the expression of multiple inflammatory cytokines, including MCP-1, IL-12, IL-6, tumor necrosis factor alpha (TNF-a), as well as IFN-β and IFN-y, through the activation of IFN regulatory factor3, NF-κB, and mitogen-activated protein kinases. MDA5initiated innate antiviral response through the induction of interferon (IFN)-α/β and antiviral proteins in the germ cells. In addition to the induction of innate antiviral response in the spermatogonia and spermatocytes, TLR3signaling induced germ cell apoptosis through activation of Caspase3/8.Conclusions:Mouse round and elongating spermatids abundantly express TLR11, which initiates innate immune response to T. gondii and UPEC stimulation. MDA5mediates antiviral response in round and elongating spermatids. TLR3signaling induces germ cell apoptosis through extrinsic apoptotic pathway. Data reveal the innate immune function of male mouse germ cells.