The Good, the Bad and the Ugly of Testicular Immune Regulation: A Delicate Balance Between Immune Function and Immune Privilege.

The testis is one of several immune privilege sites. These sites are necessary to decrease inflammation and immune responses that could be damaging to the host. For example, inflammation in the brain, eye or placenta could result in loss of cognitive function, vision or rejection of the semi-allogeneic fetus, respectively. In the testis, immune privilege is "good" as it is necessary for protection of the developing auto-immunogenic germ cells. However, there is also a downside or "bad" part of immune privilege, where pathogens and cancers can take advantage of this privilege and persist in the testis as a sanctuary site. Even worse, the "ugly" of privilege is how re-emerging viruses, such as Ebola and Zika viruses, can establish persistence in the testes and be sexually transmitted even months after they have been cleared from the bloodstream. In this review, we will discuss the delicate balance within the testis that provides immune privilege to protect the germ cells while still allowing for immune function to fight off pathogens and tumors.

Hypoxia inducible factor-1α (HIF-1α) is required for neural stem cell maintenance and vascular stability in the adult mouse SVZ.

HIF-1α is a hypoxia-inducible protein that regulates many cell and molecular processes, including those involved in angiogenesis and stem cell maintenance. Prior studies demonstrated constitutive HIF-1α stabilization in neural stem cells (NSCs) of the adult mouse SVZ, but its role there has not been elucidated. Here, we tested the hypothesis that HIF-1α plays an essential role in the maintenance of adult NSCs and stabilization of the SVZ vascular niche using conditional, tamoxifen-inducible Hif1a knock-out mice. We generated nestin-CreER(T2)/R26R-YFP/Hif1a(fl/fl) triple transgenic mice, to enable tamoxifen-inducible Hif1a gene inactivation in nestin-expressing NSCs within the adult SVZ. Hif1a gene deletion resulted in a significant loss of YFP(+) NSCs within the SVZ by 45 d post recombination, which was preceded by significant regression of the SVZ vasculature at 14 d, and concomitant decrease of VEGF expression by NSCs. Loss of YFP(+) NSCs following Hif1a gene inactivation in vivo was likely an indirect consequence of vascular regression, since YFP(+) neurosphere formation over serial passage was unaffected. These results identify NSC-encoded HIF-1α as an essential factor in the maintenance of the adult SVZ, and demonstrate that NSCs within the SVZ maintain the integrity of their vascular niche through HIF-1α-mediated signaling mechanisms.

Neonatal Pig Sertoli Cells Survive Xenotransplantation by Creating an Immune Modulatory Environment Involving CD4 and CD8 Regulatory T Cells.

The acute cell-mediated immune response presents a significant barrier to xenotransplantation. Immune-privileged Sertoli cells (SC) can prolong the survival of co-transplanted cells including xenogeneic islets, hepatocytes, and neurons by protecting them from immune rejection. Additionally, SC survive as allo- and xenografts without the use of any immunosuppressive drugs suggesting elucidating the survival mechanism(s) of SC could be used to improve survival of xenografts. In this study, the survival and immune response generated toward neonatal pig SC (NPSC) or neonatal pig islets (NPI), nonimmune-privileged controls, was compared after xenotransplantation into naïve Lewis rats without immune suppression. The NPSC survived throughout the study, while NPI were rejected within 9 days. Analysis of the grafts revealed that macrophages and T cells were the main immune cells infiltrating the NPSC and NPI grafts. Further characterization of the T cells within the grafts indicated that the NPSC grafts contained significantly more cluster of differentiation 4 (CD4) and cluster of differentiation 8 (CD8) regulatory T cells (Tregs) at early time points than the NPI grafts. Additionally, the presence of increased amounts of interleukin 10 (IL-10) and transforming growth factor (TGF) ß and decreased levels of tumor necrosis factor (TNF) α and apoptosis in the NPSC grafts compared to NPI grafts suggests the presence of regulatory immune cells in the NPSC grafts. The NPSC expressed several immunoregulatory factors such as TGFß, thrombospondin-1 (THBS1), indoleamine-pyrrole 2,3-dioxygenase, and galectin-1, which could promote the recruitment of these regulatory immune cells to the NPSC grafts. In contrast, NPI grafts had fewer Tregs and increased apoptosis and inflammation (increased TNFα, decreased IL-10 and TGFß) suggestive of cytotoxic immune cells that contribute to their early rejection. Collectively, our data suggest that a regulatory graft environment with regulatory immune cells including CD4 and CD8 Tregs in NPSC grafts could be attributed to the prolonged survival of the NPSC xenografts.

Metabolic benefits of annatto-extracted tocotrienol on glucose homeostasis, inflammation, and gut microbiome.

Emerging evidence suggests that the gut microbiome plays an important role in the pathophysiology of both obesity and type 2 diabetes mellitus. We previously reported that dietary annatto-extracted tocotrienol exerts beneficial effects by modulating inflammatory responses in mice fed a high-fat diet (HFD). The purpose of this study was to test the hypothesis that tocotrienol supplementation when combined with an HFD would result in an altered gut microbiota composition. For 14 weeks, forty-eight male C57BL/6J mice were assigned to 4 groups-low-fat diet, HFD, HFD supplemented with annatto-extracted tocotrienol at 800 mg/kg diet (AT), and HFD supplemented with metformin at 200 mg/kg diet. Glucose homeostasis was assessed by glucose and insulin tolerance tests, serum and pancreas insulin levels, and histological assessments of insulin and glucagon in pancreatic tissue. The concentrations of adipokines were measured in white adipose tissues. For the gut microbiome analysis, cecal content was collected, DNA was extracted, and 16S rRNA gene sequencing was performed. AT supplementation improved glucose homeostasis and lowered resistin, leptin, and interleukin-6 levels in white adipose tissue. Relative to the HFD group, AT-supplemented mice showed a decrease in the Firmicutes to Bacteroidetes ratio and had a lower abundance of Ruminococcus lactaris, Dorea longicatena, and Lachnospiraceae family. The relative abundance of Akkermansia muciniphila was increased in the AT group compared to the low-fat diet group. The association between the metabolic improvements and the identified bacterial taxa suggests a potential metabolic modulation caused by AT supplementation through the gut microbiota composition in mice fed an HFD.

Xenotransplanted Pig Sertoli Cells Inhibit Both the Alternative and Classical Pathways of Complement-Mediated Cell Lysis While Pig Islets Are Killed.

Xenotransplantation has vast clinical potential but is limited by the potent immune responses generated against xenogeneic tissue. Immune-privileged Sertoli cells (SCs) survive xenotransplantation long term (≥90 days) without immunosuppression, making SCs an ideal model to identify xenograft survival mechanisms. Xenograft rejection includes the binding of natural and induced antibodies and the activation of the complement cascade. Using an in vitro cytotoxicity assay, wherein cells were cultured with human serum and complement, we demonstrated that neonatal pig SCs (NPSCs) are resistant to complement-mediated cell lysis and express complement inhibitory factors, membrane cofactor protein (MCP; CD46), and decay- accelerating factor (DAF; CD55) at significantly higher levels than neonatal pig islets (NPIs), which served as non-immune-privileged controls. After xenotransplantation into naive Lewis rats, NPSCs survived throughout the study, while NPIs were rejected within 9 days. Serum antibodies, and antibody and complement deposition within the grafts were analyzed. Compared to preformed circulating anti-pig IgM antibodies, no significant increase in IgM production against NPSCs or NPIs was observed, while IgM deposition was detected from day 6 onward in both sets of grafts. A late serum IgG response was detected in NPSC (days 13 and 20) and NPI (day 20) recipients. Consistently, IgG deposition was first detected at days 9 and 13 in NPSC and NPI grafts, respectively. Interestingly, C3 was deposited at days 1 and 3 in NPI grafts and only at day 1 in NPSC grafts, while membrane attack complex (MAC) deposition was only detected in NPI grafts (at days 1-4). Collectively, these data suggest NPSCs actively inhibit both the alternative and classical pathways of complement-mediated cell lysis, while the alternative pathway plays a role in rejecting NPIs. Ultimately, inhibiting the alternative pathway along with transplanting xenogeneic tissue from transgenic pigs (expressing human complement inhibitory factors) could prolong the survival of xenogeneic cells without immunosuppression.