The role of germinal epithelium and spermatogenesis in the privileged survival of intratesticular grafts

An overview of a Sertoli cell transplantation model to study testis morphogenesis and the role of the Sertoli cells in immune privilege

Advanced testicular germ cells, expressing novel cell surface and intracellular proteins, appear after the establishment of central tolerance and thus are auto-immunogenic. However, due to testis immune privilege these germ cells normally do not evoke a detrimental immune response. The Sertoli cell (SC) barrier (also known as the blood-testis barrier) creates a unique microenvironment required for the completion of spermatogenesis and sequesters the majority of the advanced germ cells from the immune system. Given that an intact SC barrier is necessary for spermatogenesis and that disruption of the SC barrier results in loss of advanced germ cells independent of an immune response, this dual role of the SC barrier makes it difficult to directly test the importance of the SC barrier in immune privilege. The ability of SCs to survive and protect co-grafted cells when transplanted ectopically (outside the testis) across immunological barriers is well-documented. Here, we will discuss the use of a SC transplantation model to investigate the role of SC and the SC barrier in immune privilege. Additionally, the formation of cord/tubule like structures in this model, containing both SCs and myoid cells, further extends its application to study testis morphogenesis. We will also discuss the potential use of this model to study the effects of drugs/environmental toxins on testis morphogenesis, tight junction formation and SC-myoid cell interactions.

Genetically engineered immune privileged Sertoli cells: A new road to cell based gene therapy

Sertoli cells are immune privileged cells, important for controlling the immune response to male germ cells as well as maintaining the tolerogenic environment in the testis. Additionally, ectopic Sertoli cells have been shown to survive and protect co-grafted cells when transplanted across immunological barriers. The survival of ectopic Sertoli cells has led to the idea that they could be used in cell based gene therapy. In this review, we provide a brief overview of testis immune privilege and Sertoli cell transplantation, factors contributing to Sertoli cell immune privilege, the challenges faced by viral vector gene therapy, the use of immune privileged cells in cell based gene therapy and describe several recent studies on the use of genetically engineered Sertoli cells to provide continuous delivery of therapeutic proteins.

Cell lines: Valuable tools or useless artifacts

Cell lines are often used in place of primary cells to study biological processes. However, care must be taken when interpreting the results as cell lines do not always accurately replicate the primary cells. In this article, we will briefly talk about advantages and disadvantages of cell lines and then discuss results using the mouse Sertoli cell line, MSC-1, compared with primary mouse Sertoli cells. MSC-1 cells resemble Sertoli cells morphologically and possess several biochemical markers associated with Sertoli cells. Studies have demonstrated that the function and regulation of retinoic acid receptor α (RARα) is similar between MSC-1 and rat Sertoli cells. However, MSC-1 cells lack some of the immune privilege properties associated with primary Sertoli cells, including survival in animals with a fully functional immune system. Therefore, it has to be kept in mind that cell lines do not behave identically with primary cells and should not be used to replace primary cells. In order to strengthen the findings, key control experiments using primary cells should always be performed.

Reduced immunogenicity of induced pluripotent stem cells derived from Sertoli cells

Sertoli cells constitute the structural framework in testis and provide an immune-privileged environment for germ cells. Induced pluripotent stem cells (iPS cells) resemble embryonic stem cells (ES cells) and are generated from somatic cells by expression of specific reprogramming transcription factors. Here, we used C57BL/6 (B6) Sertoli cells to generate iPS cells (Ser-iPS cells) and compared the immunogenicity of Ser-iPS cells with iPS cells derived from mouse embryonic fibroblast (MEF-iPS cells). Ser-iPS cells were injected into syngeneic mice to test for their in vivo immunogenicity in teratoma assay. Teratoma assay allows assessing in vivo immunogenicity of iPS cells and of their differentiated progeny simultaneously. We observed that early-passage Ser-iPS cells formed more teratomas with less immune cell infiltration and tissue damage and necrosis than MEF-iPS cells. Differentiating Ser-iPS cells in embryoid bodies (EBs) showed reduced T cell activation potential compared to MEF-iPS cells, which was similar to syngeneic ES cells. However, Ser-iPS cells lost their reduced immunogenicity in vivo after extended passaging in vitro and late-passage Ser-iPS cells exhibited an immunogenicity similar to MEF-iPS cells. These findings indicate that early-passage Ser-iPS cells retain some somatic memory of Sertoli cells that impacts on immunogenicity of iPS cells and iPS cell-derived cells in vivo and in vitro. Our data suggest that immune-privileged Sertoli cells might represent a preferred source for iPS cell generation, if it comes to the use of iPS cell-derived cells for transplantation.

The Warburg effect revisited--lesson from the Sertoli cell

Otto Warburg observed that cancerous cells prefer fermentative instead of oxidative metabolism of glucose, although the former is in theory less efficient. Since Warburg's pioneering works, special attention has been given to this difference in cell metabolism. The Warburg effect has been implicated in cell transformation, immortalization, and proliferation during tumorigenesis. Cancer cells display enhanced glycolytic activity, which is correlated with high proliferation, and thus, glycolysis appears to be an excellent candidate to target cancer cells. Nevertheless, little attention has been given to noncancerous cells that exhibit a "Warburg-like" metabolism with slight, but perhaps crucial, alterations that may provide new directions to develop new and effective anticancer therapies. Within the testis, the somatic Sertoli cell (SC) presents several common metabolic features analogous to cancer cells, and a clear "Warburg-like" metabolism. Nevertheless, SCs actively proliferate only during a specific time period, ceasing to divide in most species after puberty, when they become terminally differentiated. The special metabolic features of SC, as well as progression from the immature but proliferative state, to the mature nonproliferative state, where a high glycolytic activity is maintained, make these cells unique and a good model to discuss new perspectives on the Warburg effect. Herein we provide new insight on how the somatic SC may be a source of new and exciting information concerning the Warburg effect and cell proliferation.

Immunoprotective properties of primary Sertoli cells in mice: potential functional pathways that confer immune privilege

Primary Sertoli cells isolated from mouse testes survive when transplanted across immunological barriers and protect cotransplanted allogeneic and xenogeneic cells from rejection in rodent models. In contrast, the mouse Sertoli cell line (MSC-1) lacks immunoprotective properties associated with primary Sertoli cells. In this study, enriched primary Sertoli cells or MSC-1 cells were transplanted as allografts into the renal subcapsular area of naive BALB/c mice, and their survival in graft sites was compared. While Sertoli cells were detected within the grafts with 100% graft survival throughout the 20-day study, MSC-1 cells were rejected between 11 and 14 days, with 0% graft survival at 20 days posttransplantation. Nonetheless, the mechanism for primary Sertoli cell survival and immunoprotection remains unresolved. To identify immune factors or functional pathways potentially responsible for immune privilege, gene expression profiles of enriched primary Sertoli cells were compared with those of MSC-1 cells. Microarray analysis identified 2369 genes in enriched primary Sertoli cells that were differentially expressed at ±4-fold or higher levels than in MSC-1 cells. Ontological analyses identified multiple immune pathways, which were used to generate a list of 340 immune-related genes. Three functions were identified in primary Sertoli cells as potentially important for establishing immune privilege: suppression of inflammation by specific cytokines and prostanoid molecules, slowing of leukocyte migration by controlled cell junctions and actin polymerization, and inhibition of complement activation and membrane-associated cell lysis. These results increase our understanding of testicular immune privilege and, in the long-term, could lead to improvements in transplantation success.

Immunological, paracrine and endocrine aspects of testicular immune privilege

Protection of the spermatogenic cells from the host immune response is fundamental to male fertility. Significantly, this protection extends to the tolerance of foreign tissue grafts placed within the testicular environment, a phenomenon that is called 'immune privilege'. This privilege of the testis appears to involve several levels of immune control, encompassing the normal mechanisms of immune tolerance, antigen sequestration behind the blood-testis barrier, reduced immune activation, localised immunosuppression and antigen-specific immunoregulation. Central to these regulatory processes are the somatic cells of the testis, particularly the Sertoli cells, and testicular secretions, including androgens, cytokines, peptides and bioactive lipids. Failure of these protective mechanisms, which may be precipitated by trauma, inflammation or infection, or as the consequence of genetic factors, can lead to androgen deficiency, infertility and autoimmunity.

Immunoprotective Sertoli cells: making allogeneic and xenogeneic transplantation feasible

The testis as an immune-privileged site allows long-term survival of allogeneic and xenogeneic transplants. Testicular Sertoli cells (SCs) play a major role in this immunoprotection and have been used to create an ectopic immune-privileged environment that prolongs survival of co-transplanted allogeneic and xenogeneic cells, including pancreatic islets and neurons. Extended survival of such grafts testifies to the immunoprotective properties of SCs. However, there is still variability in the survival rates of the co-grafted cells and rarely are 100% of the grafts protected. This emphasizes the need to learn more about what is involved in creating the optimal immunoprotective milieu. Several parameters including organization of the SCs into tubule-like structures and the production of immunomodulatory factors by SCs, specifically complement inhibitors, cytokines, and cytotoxic lymphocyte inhibitors, are likely important. In addition, an intricate interplay between several of these factors may be responsible for providing the most ideal environment for protection of the co-transplants by SCs. In this review, we will also briefly describe a novel use for the immune-privileged abilities of SCs; engineering them to deliver therapeutic proteins for the treatment of diseases like diabetes and Parkinson's disease. In conclusion, further studies and more detailed analysis of the mechanisms involved in creating the immune-protective environment by SCs may make their application in co-transplantation and as engineered cells clinically feasible.

Sertoli cell line lacks the immunoprotective properties associated with primary Sertoli cells

Sertoli cells are important for maintenance of the immune privileged environment of the testis and prolong survival of cotransplanted cells. The objective of the current study was to examine the immunoprotective properties of a mouse Sertoli cell line (MSC-1) in order to identify a Sertoli cell line that could be used to aid in investigation of the immunoprotective abilities of Sertoli cells. BALB/c islets were cotransplanted with 0-9 million primary BALB/c Sertoli cells or MSC-1 cells into diabetic C3H or BALB/c mice and protection of grafted islets was examined by monitoring blood glucose levels and immunohistochemical analysis. Additionally, expression of potential immunoprotective factors in MSC-1 cells was examined. Cotransplantation of islets with 3 million primary Sertoli cells significantly prolonged islet allograft survival (61.1 +/- 6.9 days; p < 0.05) compared with control mice that received allogeneic islets alone (26.9 +/- 2.1 days). Grafts collected from normoglycemic C3H mice at 100 days posttransplant contained insulin-positive beta-cells adjacent to allogeneic Sertoli cells arranged in tubule-like structures. In contrast, cotransplantation of islet allografts with MSC-1 cells did not prolong islet survival (average 29.8 +/- 3.3 days) regardless of the number of MSC-1 cells transplanted and the rejected grafts contained very few beta-cells and randomly arranged MSC-1 cells. The lack of islet cell survival was not due to detrimental effects of MSC-1 cells because syngneic islets cotransplanted with MSC-1 cells were functional throughout the study. MSC-1 cells were found to express known Sertoli cell-expressed, immunoprotective factors, clusterin, Fas ligand, and transforming growth factor-beta1, suggesting additional factors may be involved in Sertoli cell immune privilege. These data indicate the MSC-1 cell line lacks the immunoprotective properties associated with primary Sertoli cells. Further study of this cell line could be useful in examining the mechanisms that enable Sertoli cells to provide immune privilege.

Comparison of successful and unsuccessful islet/Sertoli cell cotransplant grafts in streptozotocin-induced diabetic mice

Sertoli cells (SC) protect islet allografts from immune destruction in diabetic rodents. In this study, we examined the difference between successful and rejected islet/SC cografts in order to further improve this procedure for optimal extension of islet allograft survival. We cotransplanted 500 BALB/c islets with 1-8 million BALB/c SC under the kidney capsule of diabetic BALB/c, C3H-HeJ, and C57BL/6 mice. Cotransplantation of islets with up to 8 million SC was not detrimental to long-term islet graft function in syngeneic mice. However, large numbers of SC were detrimental to islet graft survival in allogeneic mice with the optimal dose for cotransplantation of 4 or 1 million SC in C3H-HeJ or C57BL/6 mice, respectively. Examination of successful grafts, from euglycemic recipients, revealed the presence of SC arranged in tubule structures with islets surrounding these tubules. Cellular infiltrate in successful grafts revealed CD4 T cells and macrophages along the periphery and within the grafts, and very few CD8 T cells. Conversely, examination of unsuccessful grafts, harvested from hyperglycemic recipients at the time of rejection, revealed the presence of SC arranged randomly with islets adjacent to the Sertoli cells, when present, and massive CD4 and CD8 T cell as well as macrophage cell infiltration. Prolongation of islet allograft survival appeared to be a function of SC transplant mass and recipient genetic background. A consequence of long-term graft acceptance is the formation of SC tubule structures, which may be an additional requirement for optimal protection of islet allografts.

In vivo immune modulatory activity of hepatic stellate cells in mice

Accumulating data suggest that hepatic tolerance, initially demonstrated by spontaneous acceptance of liver allografts in many species, results from an immune regulatory activity occurring in the liver. However, the responsible cellular and molecular components have not been completely understood. We have recently described profound T cell inhibitory activity of hepatic stellate cells (HSCs) in vitro. In this study, we demonstrate in vivo evidence of immune modulatory activity of HSCs in mice using an islet transplantation model. Co-transplanted HSCs effectively protected islet allografts from rejection, forming a multi-layered capsule, which reduced allograft immunocyte infiltrates by enhancement of apoptotic death. The immune modulation by HSCs appeared to be a local effect, and regulated by inducible expression of B7-H1, an inhibitory molecule of B7 family. This may reflect an intrinsic mechanism of immune inhibition mediated by liver-derived tissue cells. In conclusion, these results may lead to better understanding of liver immunobiology and development of new strategies for treatment of liver diseases.

Tissue microcircumstances for leukocytic infiltration into the testis and epididymis in mice

Spermatozoa do not appear in the seminiferous epithelium until puberty, when immune tolerance has already been established. Therefore, they contain various autoimmunogenic materials which are recognized as foreign by the self immune system. However, the testis and epididymis are known as immunologically privileged organs. In particular, the blood-testis barrier (BTB) formed by Sertoli cells and the blood-epididymal barrier formed by epididymal epithelial cells protect autoimmunogeneic spermatozoa from attack by the self immune system. The immune privileged circumstances in the testis and epididymis have been demonstrated by many studies to involve a local transplantation system. We review here the immune privileged status of these organs from the viewpoint of induction of inflammatory cell responses in mice. The testicular interstitium in mice is resistant to vasculitis, lymphangitis, spermatic granuloma and polymorphonuclear cell infiltration: however, the epididymal interstitium is vulnerable to them. Therefore, the testicular tissue outside BTB is also protected from inflammatory cell infiltration, although many resident macrophages are normally present in the testis. In sharp contrast, subcutaneous injection of viable syngeneic testicular germ cells (TGC) alone induces autoimmune orchitis with no involvement of the epididymitis in mice. In the testes of TGC-immunized animals, severe lymphocytic infiltration with aspermatogenesis was seen in spite of no use of adjuvants. Unexpectedly, injections of viable epididymal spermatozoa (ES) did not evoke any autoimmune inflammation in the epididymides. Therefore, the testis rather than the epididymis may easily become an unprivileged organ as to autoimmunity under some special conditions.

Neonatal Porcine Sertoli Cells Inhibit Human Natural Antibody-Mediated Lysis1

Sertoli cells protect cotransplanted cells from allogeneic and xenogeneic rejection. Additionally, neonatal porcine Sertoli cells (NPSCs) survive long-term as xenografts in nonimmunosuppressed rodents. This has led to the hypothesis that NPSCs could be used to prevent cellular rejection in clinical transplantation, thereby eliminating the need for chronic immunosuppression. Prior to transplantation of NPSCs in humans it is necessary to determine whether they are also protected from humoral-mediated xenograft rejection. The presence of Gal alpha(1,3)Gal beta(1,4)GlcNAc-R (alphaGal epitope) as well as binding of human immunoglobulin G (IgG) and IgM to NPSCs was examined by immunocytochemical and fluorescence-activated cell sorter analysis. alphaGal was detected on 88.5% +/- 3.0% of NPSCs. Consistent with this, 71.7% +/- 1.0% and 65.4% +/- 5.2% of NPSCs were bound by IgG and IgM, respectively. When cultured NPSCs underwent an in vitro cytotoxicity assay by incubation with human AB serum plus complement, no increase in cellular lysis was observed, while controls--porcine aorta endothelial cells--were shown to contain > 60% dead cells. Finally, activation of the complement cascade was examined by immunohistochemistry. C3 and C4 were deposited on the surface of the NPSC membrane, indicating activation of complement. Although the complement cascade was activated, the membrane attack complex (MAC) was not formed. These data demonstrate that despite expression of alphaGal, binding of xenoreactive antibodies, and the activation of complement, NPSCs survive human antibody and complement-mediated lysis by preventing MAC formation. This suggests that NPSCs may be able to survive humoral-mediated rejection in a clinical situation.

Genetically engineered Sertoli cells are able to survive allogeneic transplantation

The immunoprotective nature of the testis has led to numerous investigations for its ability to protect cellular grafts. Sertoli cells (SCs) are at least partially responsible for this immunoprotective environment and survive allogeneic and xenogeneic transplantation. The ability of SCs to survive transplantation leads to the possibility that they could be engineered to deliver therapeutic proteins. As a model to test this hypothesis, we examined the ability of SCs that produce green fluorescent protein (GFP) to survive transplantation and continue expressing GFP. SCs were isolated from transgenic mice engineered to express GFP and transplanted as aggregates under the kidney capsule of severe combined immunodeficient (SCID) and Balb/c mice. Using this paradigm, it was possible to compare the survival of transgenic SCs directly in both immunodeficient and immunocompetent recipients. Fluorescence microscopy of the kidney capsule and immunohistochemistry of the grafts for GFP and GATA-4 revealed the presence of GFP-expressing SCs under the kidney capsule of SCID and Balb/c mice at both 30 and 60 days post-transplantation. In contrast, islets transplanted to Balb/c mice were rejected. Thus, SCs survive transplantation and continue to express GFP raising the possibility that SCs can be engineered using transgenic technology to produce proteins, such as insulin, factor VIII, or dopamine for the treatment of diabetes, hemophilia or Parkinson's disease, respectively.

Long-term survival of neonatal porcine Sertoli cells in non-immunosuppressed rats

Sertoli cells from the testis contain immunoprotective properties which allow them to survive as allografts and also to protect islets and adrenal chromafin cells from immune rejection without the use of immunosuppressive drugs. Experiments were designed to determine whether xenogeneic neonatal porcine Sertoli cells (NPSCs) survive transplantation in rats without the use of immunosuppression. NPSCs (92.2 +/- 5.1%) were isolated, cultured and then transplanted under the kidney capsule of non-immunosuppressed Lewis rats. To assess survival, grafts were removed after 4, 20, 30, 40, 60, and 90 days post-transplant and immunostained for the Sertoli cell marker vimentin. Survival was confirmed by polymerase chain reaction (PCR) for the porcine mitochondrial cytochrome oxidase II (COII) subunit gene, a marker for porcine tissue. In both methods, NPSCs were detected in the grafts for at least 90 days. Histologically, NPSCs were clustered in small aggregates or organized in tubule-like structures. When stained for the presence of proliferating cell nuclear antigen (PCNA), many Sertoli cells stained positive at 20 days post-transplant, indicating not only cell survival but also Sertoli cell proliferation. The number of PCNA positive cells decreased somewhat by 40 days with almost no positive Sertoli cells at 60 and 90 days. These data demonstrate that NPSCs survive long-term following xenotransplantation in rats, which to our knowledge is the first report of a discordant xenograft surviving without immunosuppression in a non-immunoprivileged site. Further study of the mechanism of NPSC xenograft survival may provide clues for promoting a local tolerogenic environment.

Harnessing the Immunomodulatory Properties of Sertoli Cells to Enable Xenotransplantation in Type I Diabetes

Islet transplantation has emerged as a viable long-term means of treating type I diabetes. This is largely due to the success of the "Edmonton protocol" which has produced insulin independence in 85% of patients 1 year after transplantation of allogeneic islets together with a non-steroid immunosuppressive regimen. While these data provide a clear and unequivocal demonstration that islet transplantation is a viable treatment strategy, the shortage of suitable donor tissue together with the debilitating consequences of life-long immunosuppression necessitate the development of novel means to enable transplantation of all type 1 diabetics including the young juvenile diabetics. One potential means of enabling islet transplantation takes advantage of the ability of Sertoli cells to provide local immunoprotection to co-grafted islets, including those from xenogeneic sources. Sertoli cells are normally found in the testes where one of their functions is to provide local immunologic protection to developing germ cells. In animal models, allogeneic and xenogeneic islets survive and function for extended periods of time when grafted into the testes. Moreover, isolated Sertoli cells protect co-grafted allogeneic and xenogeneic islets from immune destruction and reverse diabetes in immunocompetent and autoimmune animals. These benefits are discussed in the context of several potential underlying biological mechanisms.

Germ cell transplantation in goats

Transplantation of spermatogonial stem cells provides a unique approach for the study of spermatogenesis and manipulation of the male germ line. This technique may also offer an alternative to the currently inefficient methods of producing transgenic domestic animals. We have recently established the technique of spermatogonial transplantation, originally developed in laboratory rodents, in pigs, and this study was aimed to extend the technique to the goat. Isolated donor testis cells were infused into the seminiferous tubules of anesthetized recipient goats through an ultrasonographically-guided catheter inserted into the rete testis. Donor cells were obtained by enzymatic digestion of freshly collected testes from immature goats (either from the recipients' contralateral testis or from unrelated donors). Prior to transplantation, testis cells were labeled with a fluorescent marker to allow identification after transplantation. Recipient testes were examined for the presence and localization of labeled donor cells at 3-week intervals up to 12 weeks after transplantation. Labeled donor cells were found in the seminiferous tubules of all testes, comprising 10-35% of the examined tubules. Histological examination of the recipient testes did not reveal evident tissue damage, except for limited fibrotic changes at the site of needle insertion. Likewise there were no detectable local or systemic signs of immunologic reactions to the transplantations. These results indicate that germ cell transplantation is technically feasible in immature male goats and that donor-derived cells are retained in the recipient testis for at least three months and through puberty. This study represents the first report of germ cell transplantation in goats.

Germ cell transplantation in goats

Transplantation of spermatogonial stem cells provides a unique approach for the study of spermatogenesis and manipulation of the male germ line. This technique may also offer an alternative to the currently inefficient methods of producing transgenic domestic animals. We have recently established the technique of spermatogonial transplantation, originally developed in laboratory rodents, in pigs, and this study was aimed to extend the technique to the goat. Isolated donor testis cells were infused into the seminiferous tubules of anesthetized recipient goats through an ultrasonographically-guided catheter inserted into the rete testis. Donor cells were obtained by enzymatic digestion of freshly collected testes from immature goats (either from the recipients' contralateral testis or from unrelated donors). Prior to transplantation, testis cells were labeled with a fluorescent marker to allow identification after transplantation. Recipient testes were examined for the presence and localization of labeled donor cells at 3-week intervals up to 12 weeks after transplantation. Labeled donor cells were found in the seminiferous tubules of all testes, comprising 10-35% of the examined tubules. Histological examination of the recipient testes did not reveal evident tissue damage, except for limited fibrotic changes at the site of needle insertion. Likewise there were no detectable local or systemic signs of immunologic reactions to the transplantations. These results indicate that germ cell transplantation is technically feasible in immature male goats and that donor-derived cells are retained in the recipient testis for at least three months and through puberty. This study represents the first report of germ cell transplantation in goats.

Leydig cell apoptosis after the administration of ethane dimethanesulfonate to the adult male rat is a Fas-mediated process

Leydig cells undergo apoptosis in response to the cytotoxin ethane dimethanesulfonate (EDS), with numbers declining at 12-18 h and maximal apoptosis at 24 h postinjection. The Bcl-2 family members, Bcl-2, Bcl-xl, and Bax, appear not to be involved in this process. To further investigate this phenomena, a single dose of EDS was administered to adult rats to induce the killing of Leydig cells. The interstitial cells were examined up to 3 days after EDS administration by Western blot analysis for the Bcl-2 family members (Bak and Bcl-w). Western blotting showed that Bak expression in the interstitial cell preparations was unchanged after EDS, and immunohistochemistry showed that it was not up-regulated in Leydig cells in response to EDS. Bcl-w expression in the Leydig cells and interstitial cell preparations was unchanged until 48 h when it became undetectable, suggesting that Leydig cell-associated Bcl-w is not involved in initiating apoptosis. We also investigated the role of the Fas system in Leydig cell apoptosis. Both Fas receptor and Fas ligand protein levels increased after EDS, peaking at 12-18 h and declining thereafter. Fas receptor and ligand were shown by immunohistochemistry to be present in Leydig cells, and after EDS all Leydig cells became strongly positive for both proteins. The intensity of staining increased in the early stages of apoptosis and decreased as the nuclear morphology became more fragmented. These data suggest that Bcl-2 family members are not involved in Leydig cell apoptosis after EDS administration. However, up-regulation of the Fas system does occur, implicating activation of Fas receptor in the induction of Leydig cell apoptosis.

Potential application of neonatal porcine islets as treatment for type 1 diabetes: a review

Islet transplantation has been shown to be a viable option for treating patients with type 1 diabetes. However, widespread clinical application of this treatment will necessitate an alternative source of insulin-producing tissue. Porcine pancreata may be a potential source of islets since pigs are inexpensive, readily available, and exhibit morphological and physiological characteristics comparable to humans. Recently, we developed a simple, standardized procedure for isolating large numbers of neonatal porcine islets with a reproducible and defined cellular composition. Following nine days of in vitro culture, tissue from one neonatal pig pancreas yielded approximately 50,000 islet cell aggregates, consisting of primarily epithelial cells (57%) and pancreatic endocrine cells (35%). In addition, neonatal porcine islets were responsive to glucose challenge in vitro and were capable of correcting hyperglycemia in alloxan-induced diabetic nude mice. Although neonatal porcine islets constitute an attractive alternative source of insulin-producing tissue for clinical transplantation, many aspects such as the immunological responses to these tissue and the latent period (2 to 8 weeks) between transplantation of these islets and the reversal of hyperglycemia need further investigation. This article discusses these issues and presents possible solutions to problems that may hinder the potential application of neonatal porcine islets for transplantation into patients with type 1 diabetes.

A role for CD95 ligand in preventing graft rejection

Testis is a remarkable immune-privileged site, long known for its ability to support allogeneic and xenogeneic tissue transplants. Here we have investigated the molecular basis for testis immune privilege. Testis grafts derived from mice that can express functional CD95 (Fas or Apo-1) ligand survived indefinitely when transplanted under the kidney capsule of allogeneic animals, whereas testis grafts derived from mutant gld mice, which express non-functional ligand, were rejected. Further analysis of testis showed that CD95 ligand messenger RNA is constitutively expressed by testicular Sertoli cells, and that Sertoli cells from normal mice, but not gld mice, were accepted when transplanted into allogeneic recipients. CD95 ligand expression in the testis probably acts by inducing apoptotic cell death of CD95-expressing, recipient T cells activated in response to graft antigens. These findings indicate that CD95 ligand could be used to create immune-privileged tissue for a variety of transplant uses.

Immunology of the testicular excurrent ducts

The sperm autoantigen concentration in the epididymis equals or exceeds that in the testis. This makes the epididymis a probable site of initiation of an antisperm autoimmune response. The mechanisms regulating antisperm antibody formation in the testicular excurrent ducts and some related aspects with clinical interest are reviewed.

A new murine model of autoimmune orchitis induced by immunization with viable syngeneic testicular germ cells alone. II. Immunohistochemical findings of fully-developed inflammatory lesion

Previous studies demonstrated that experimental autoimmune orchitis (EAO) was produced in C3H/He mice with very high incidence by two or three subcutaneous injections of viable syngeneic testicular germ cells, without the use of any adjuvants or immunopotentiators and that the disease induced was characterized by a complete lack of epididymitis despite a definite orchitis with hypospermatogenesis. In this report, immunohistochemical characterization of immune cells in the fully-developed orchitic lesion was carried out using monoclonal antibodies and immunoperoxidase staining. Thy-1.2+ cells, Mac-1+ cells, B220+ cells and cytoplasmic Ig-bearing cells in the lesion were estimated to be approximately 30, 15, 20 and 30% of all inflammatory cells, respectively. Major phenotype of T cells in the lesion was CD4+ (approximately 85%) with the remainder (approximately 15%) being CD8+. The percentages of cytoplasmic IgG-, IgA- and IgM-bearing cells were estimated as approximately 35, 60 and 5% of all cytoplasmic Ig-bearing cells, respectively. Deposits of immunoglobulins and third component of complement were identified on the basement membrane of the seminiferous tubules, interstitium between the tubules, vessel endothelium and degenerated germ cells in the lesion. Circulating antibodies directed against the acrosomal portion of germ cells were detected in IgG and IgM classes but not in IgA class. Inflammatory cells (including macrophages, B cells and, probably, activated T cells) in the lesion were Ia+, but Leydig cells, Sertoli cells and germ cells did not stain for Ia at all.

Testicular immunoregulatory factors

The present data indicate that immune cells are regulated locally in the testis by Leydig cells, Sertoli cells and resident testicular macrophages. The effects of these cells are mediated by several peptide factors, including protectin, a group of high molecular weight testicular immunosuppressive factors, and testicular interleukin-1 alpha-like factor. The testicular interleukin-1 alpha-like factor is produced by Sertoli cells and is under hypophyseal control. Its synthesis starts at puberty concomitantly with the onset of spermatogenesis and it may act as a spermatogonial growth factor. Protectin, which is under hypophyseal control, may be involved in the mechanism of prolonged transplant survival in the testicular interstitial tissue. Its levels increase at puberty. Both the testicular interleukin-1 alpha-like activity and protectin may be important in testicular pathophysiology.

Recent evidence for immune privilege in the testis

In the last 20 years, it has been shown that while first-set intra-testicular grafts rarely induce systemic immunity, second-set intra-testicular grafts are usually rejected, if a pre-existing immunity has been generated by first-set skin grafts. These observations suggest that while the efferent limb of the pre-sensitized immune response is operative in the testis, the immune system can not be activated against antigens present only in this site. Various theories have been advanced to explain this phenomenon. The most likely explanation at present seems to be that the testis contains specific immunosuppressive factors that inhibit lymphocyte activation in this site.

Testicular immunosuppressive protein

Auto-, allo- and xenografts of various endocrine tissues survive for prolonged periods in the testicular interstitium. The reason for transplant survival outside the blood-testis barrier has been obscure. In the present paper we describe a high molecular weight (Mr = 130,000), heat- and pH-labile immunosuppressive factor with an isoelectric point of 6.3-7.3 in extracellular fluid collected from the rat testicular interstitium. The results show that the testicular immunosuppressive agent is not a steroid, but a protein. This testicular immunosuppressive protein may contribute to the immune privilege in the testicular interstitium.

Fetal and postnatal testis shows immunoprivilege as donor tissue

We evaluated the immunogenicity of the testis by transplanting adult, postnatal, and fetal rat testicular tissue into outbred adult female and male rats for 10 days. Testis grafts were evaluated morphometrically and histologically, and selectively compared to renal grafts previously reported in part. Testis grafts from days 15 to 21 of gestation, and from three, nine, 12 and 15 days after birth showed an overall increase in growth, with maintenance of architecture and minimal lymphocytic infiltrate. In contrast, only fetal renal tissue from days 15 to 17 demonstrated an increase in growth with maintenance of architecture and minimal lymphocytic infiltrate; grafts from later in gestation grew only slightly and showed progressive deterioration in architecture with an increasing lymphocytic infiltrate. Fifteen day fetal testis grafts were also implanted for longer intervals up to 45 days. The fetal testis grafts implanted for 20 and 30 days showed an increase in size with maintenance of architecture and minimal lymphocytic infiltrate. The observed fetal and postnatal testis growth in the non-immunosuppressed adult host makes compelling further studies directed at determining those factors contributing to the decreased immunogenicity of this organ.