Fas ligand expression in colon cancer:A possible mechanism of tumor immune privilege

AIM: To detect the expression of Fas ligand (FasL) in colon cancer tissues and cell lines and analyze the function of FasL-expressing colon cancer cells in inducing Fas-sensitive T lymphocyte apoptosis. METHODS: Ninety surgically resected colon cancer tissues and 15 hepatic metastasis specimens were investigatedby immunohistochemical method with normal colon mucosa and colon adenoma as control. The relationship between FasL expression and pathologic features was also analyzed.FasL expression of 4 colon cancer cell lines, SW620, Lovo, LS-174T and SW1116, were detected by Western blotting assay. The function of FasL expressed on colon cancer cells was determined by coculture assay with Jurkat T lymphocytes, the apoptotic rate of which was detectedby flow cytometry assay.RESULTS: Fifty-six (62.22%) cases of all the 90 colon cancer tissues and all (100%) the liver metastasis specimens expressed FasL, significantly higher than normal colon mucosa and colonic adenoma. Higher expression of FasL was found in more advanced stage of colon cancer and in cancer tissues with lymphatic or hepatic metastasis.All the colon cancer cell lines were found to express FasL.After coculture with the SW1116 cells for 24 h with an effector: target ratio 10:1, the rate of apoptosis of Jurkat cells rose from 1.9% to 21.0%.CONCLUSION: The expression of FasL is upregulated in colon cancer and the functionally expressed FasL can induce apoptosis of Fas-expressing T lymphocytes.

Effect of Vasocation Intestinal Peptide on Immune Privilege of the Rat Testis

Objective To study the effect of vasocation intestinal peptide （VIP） on immune privilege of the rat testis. Methods The UU infected SD rats and Leydig cells were intervened by VIP, the secretion of TGF-β and the expression of FasL in rat Leydig cells were compared between VIP-intervened group and control group to test the effect of VIP on immune privilege of the rat testis in vitro and in vivo. Results In vitro, the secretion of TGF-β in Leydig cells could be increased by low dosage of VIP while inhibitited by high dosage of VIP; expression of FasL mRNA in Leydig cells could be decreased by VIP In vivo, increased expression of TGF-β mRNA and decreased FasL mRNA were observed in VIP group in 2-3 weeks after infected by UU. In addition, the apoptosis of Jurkat cells mediated by Leydig cells could be prevented by VIP Conclusion When Leydig cells or testis infected by UU, VIP could regulate the immune function of rat Leydig cells and participate in the regulation of immune privilege of testis through the regulation of TGF-β secretion and FasL expression pattern of Leydig cells.

Immune privilege induced by cotransplantation of islet and allogeneic testicular cells

Objective To induce islet allograft long-term survival through cotransplantation of islet cells with sertoli cells.Methods Testicular sertoli cells were prepared by digestion with collagenase, trypsin and DNase, and were cultured for 48 hours. Collagenase digested and Ficoll purified donor (Wistar rat) islets were cotransplanted with allogeneic sertoli cells in the absence of systemic immunosuppression. Terminal leoxynucleotidyl transferase-mediated X-dUTP nick-end labeling (TUNEL) was used to label apoptosis of lymphocytes surrounding the islet graft.Results Cotransplantation of islets and 1 × 107 sertoli cells reversed the diabetic state for more than 60days in 100% (6/6) of the chemically diabetic Sprague Dawley rats. Grafts consisting of islets alone or islets plus 1 × 105 sertoli cells survived only for 5 - 6 days. Apoptosis of lymphocytes surrounding the islets was quite clear.Conclusion Cotransplantation of islets with FasL+ sertoli cells induces local immune privilege and allows long-term graft survival without systemic immunosuppression.

Testicular defense systems： immune privilege and innate immunity

The mammalian testis possesses a special immunological environment because of its properties of remarkable immune privilege and effective local innate immunity. Testicular immune privilege protects immunogenic germ cells from systemic immune attack, and local innate immunity is important in preventing testicular microbial infections. The breakdown of local testicular immune homeostasis may lead to orchitis, an etiological factor of male infertility. The mechanisms underlying testicular immune privilege have been investigated for a long time. Increasing evidence shows that both a local immunosuppressive milieu and systemic immune tolerance are involved in maintaining testicular immune privilege status. The mechanisms underlying testicular innate immunity are emerging based on the investigation of the pattern recognition receptor-mediated innate immune response in testicular cells. This review summarizes our current understanding of testicular defense mechanisms and identifies topics that merit further investigation.

Mechanisms of testicular immune privilege

The testis exhibits a distinctive form of immune privilege to protect the germ cells from the host immuneattack. The property of testicular immune privilege was originally attributed to the blood-testis barrier in theseminiferous epithelium, which sequesters antigens. Recent studies have uncovered several levels of immune controlbesides the blood-testis barrier involved in the privilege of the testis, including the mechanisms of immune tolerance,reduced immune activation, localized active immunosuppression and antigen-specific immunoregulation. The somaticcells of the testis, especially Sertoli cells, play a key role in regulating the testicular immune privileged status. Theconstitutive expression of anti-inflammatory factors in the testis by somatic cells is essential for local immunosuppression.Growing evidence shows that androgens orchestrate the inhibition of proinflammatory factors and shift cytokinebalance toward a tolerogenic environment. Disruption of these protective mechanisms, which may be caused by trauma,infection and genetic factors, can lead to orchitis and infertility. This review article highlights the unique immuneenvironment of the testis, particularly focuses on the regulation of testicular immune privilege.

Effects of Ureaplasma Urealyticum on Fas Ligand Expression in Rat Sertoli Cell

To investigate the effect of ureaplasma urealyticum (UU) on the expression of Fas ligand (FasL) on rat Sertoli cell Materials & Method Isolated rat Sertoli cells were infected by living UU, UU super- natants, inactivated UU, then Fluorescence Activated Cell Sorter and observed fluores- cence microscopy were used to assay for the FasL expression on the surface of Sertoli cells. Results UU infection could increase the expression of FasL in Sertoli cell. Conclusion The functional expression of FasL is related to the immune privilege and can give the immune regulation on the testis.

The effect of FasL gene transfer to islet cells on pancreatic islet allografts

OBJECTIVE: To investigate the effect of FasL gene transfer to islet cells on pancreatic islet allografts. METHODS: A recombinant and replication-deficient type-5 adenovirus encoding murine FasL (AdV- FasL) was constructed by the method of calcium phosphate precipitation. Pancreatic islets were infected with the recombinant adenovirus AdV-FasL, and transplanted into diabetic recipients. FasL expression was detected by RT-PCR and immunohistochemistry. The survival of allografts and the apoptosis of gene transferred islet allografts were analyzed. RESULTS: All animals receiving islet allograft alone returned to a diabetic state by several days (mean survival time 6.3±0.6 days). Compared with the control group, no delayed rejection and prolonged survival of allografts were observed in the group of FasL gene transfer. The rejection was accelerated and the allograft survival was shortened to 3.4±0.2 days (P<0.05). Pancreatic islets infected with AdV- FasL demonstrated positive staining of FasL at 24 h, with an increased intensity at 48 h, but not in AdV-5 infected or uninfected islets. TUNEL labeling of pancreatic islet allografts at 24, 48 h revealed apoptosis that was not in AdV-5 infected allografts. CONCLUSIONS: Though co-transplantation of FasL-expressing testicular cells can induce privilege of islet allografts and prolong allograft survival, direct expression of FasL on islet allografts infected with AdV-FasL may accelerate islets rejection by islet apoptosis and granulocyte infiltration.