Characteristics of immunotolerance induced by intratesticular injection of S-antigen

Testicular-associated immune deviation: flushing of the testicular lymph sinusoids induces immunosuppression and inhibits formation of EAE in SJL mice

Injection of antigen into the testis has been previously proved to induce systemic tolerance in rats. Testicular-associated immune deviation (TAID) has thus far been induced and studied only in the rat and the present study was planned to study if TAID could be induced in mice as well. In addition, it was studied if TAID is organ-specific. Mouse spinal cord homogenate (MSCH), as well as phosphate-buffered saline (PBS), was injected into the testes of SJL and BALB/c male mice before the induction of experimental allergic encephalomyelitis into the animals. The control animals received MSCH intramuscularly into the hamstring muscles. The animals were followed and graded daily for symptoms attending the next 30 days. In the SJL strain, mice treated with an intratesticular (i.t.) MSCH injection prior to the induction of experimental autoimmune encephalomyelitis (EAE) had the shortest duration of symptoms and the longest time to the onset of the first symptoms. In addition, the mice injected i.t. with PBS had as mild symptoms as those injected with MSCH. There was a statistically significant difference, however, between the groups injected either with MSCH or PBS intratesticularly. In general, mice treated with an intramuscular injection of MSCH got sick first, and had the most severe symptoms for the longest duration of time. In the case of the BALB/c mice, there were no statistical differences between the groups investigated. It is concluded that TAID is a testis- and strain-specific phenomenon in the mouse, and not specific to the rat. In addition, i.t. injection of PBS is just as effective in creating tolerance against EAE as i.t. injection of MSCH in the SJL mice.

Regulatory cells generated by testicular tolerization to retinal S-antigen: possible involvement of IL-4, IL-10, and TGF-beta in the suppression of experimental autoimmune uveoretinitis

Intratesticular injection of a retinal protein (S-antigen) into Lewis rats induces systemic immunotolerance (designated orchidic tolerance) and renders animals refractory to experimental autoimmune uveoretinitis (EAU) produced by S-antigen immunization. We demonstrated in this work that the immunotolerance could be transferred to syngeneic naive rats by both CD4+ and CD8+ regulatory cells. Attempts were then made to characterize the cytokines involved in the immunosuppressive activity of these regulatory cells. Using the in vitro lymphoproliferation assay, the inhibitory effect of CD4+ cells on effector cells was found to be reversed by antibodies against IL-4 and IL-10 but not by anti-TGF-beta antibody. IL-4 (IC50 = 1.6 ng/10(6) cells) and IL-10 (IC50 = 0.6 ng/10(6) cells) added to the assay medium were potent inhibitors of effector cell proliferation. Increased immunoreactivity and mRNA expression for IL-4 and IL-10 was observed for CD4+ regulatory cells. The inhibitory effect of CD8+ regulatory cells was reversed by anti-TGF-beta antibody but not by antibodies against IL-4 and IL-10. Compared with control CD8+ cells, CD8+ cells from tolerized rats demonstrated higher immunoreactivity for TGF-beta but did not show an enhanced expression of mRNA for TGF-beta. TGF-beta 1 and TGF-beta 2 added to effector cells showed dichotomous effects; both isoforms stimulated cell proliferation at 2.5 ng/10(6) cells and inhibited at lower or higher concentrations. These results led us to conclude that IL-4 and IL-10 are important cytokines for the immunosuppressive effect of CD4+ regulatory cells generated in orchidic tolerance. TGF-beta is an important immunosuppressive cytokine for CD8+ regulatory cells but further studies will determine whether other cytokines are also involved.

Immunotolerance induced by intratesticular antigen priming: expression of TGF-beta, Fas and Fas ligand

The authors have previously reported that an injection of S-antigen (S-Ag) into rat testes prior to immunization induces systemic tolerance (designated orchidic tolerance) and protects the animals from experimental autoimmune uveoretinitis (EAU) and that the signal for orchidic tolerance induction emigrates from the testis within a few hours after antigen priming of the testis. In order to understand the mechanism by which the signal or signal carrier is generated, they determined in this study changes in immunoreactivity for transforming growth factor-beta (TGF-beta), IFN-gamma, IL-2, Fas and Fas ligand in the testis following an injection of S-Ag. Immunoreactivity for TGF-beta increased with time, reaching a maximum in six hours and declining thereafter. The time required for the maximum expression of TGF-beta coincided well with the time-dependent profile of orchidic tolerance signal generation within the testis. Little or no immunoreactivity was observed for IFN-gamma and IL-2 in normal (control) and S-Ag-injected testes. Immunoreactivity for Fas and Fas ligand was detected both in control and experimental testes and did not change appreciably with time following Ag-priming of the testis. Fas immunoreactivity was found in spermatids and virtually absent in the interstitial tissue, while Fas ligand immunoreactivity was primarily associated with the interstitial cells such as Leydig cells. Fas ligand immunoreactivity was very weak, if any, in the germ cells and Sertoli cells. These results suggest that TGF-beta and Fas ligand expressed in MHC-positive interstitial cells may play an important role in the generation of orchidic tolerance induction signal. A preliminary study showed that splenocytes preincubated with testis extracts and S-Ag, when transferred to naive rats, induced systemic tolerance in recipient animals. Inclusion of anti-TGF-beta or a carboxyl terminal peptide of Fas in the testis extract reduced the potency of incubated splenocytes to induce systemic tolerance in recipient rats. These results indicate that generation of the orchidic tolerance signal does not require the anatomical structure of the testis but is mediated by molecular entities such as TGF-beta and Fas ligand.

Induction of immunotolerance in rats by intratesticular administration of an eicosapeptide of bovine S-antigen

Immunization of albino LEW rats with a retinal soluble antigen (S-antigen) induces experimental autoimmune uveoretinitis (EAU) which shows clinical features resembling those of human uveitis. Several uveitogenic epitopes have been identified in the antigen. This study reports that an intratesticular injection of low doses of a uveitogenic eicosapeptide (P343-362) of S-antigen prior to immunization with the same peptide prevented the onset of EAU by inducing systemic tolerance, designated orchidic tolerance. Splenic lymphocytes of both CD4+ and CD8+ subsets from tolerized rats transferred orchidic tolerance to syngeneic recipients and protected them from subsequent EAU induction. Orchidic tolerance elicited by low antigen dosage was mediated, in part, by active suppression due to suppressor or regulatory cells. At high antigen doses, however, regulatory activity was reduced possibly due to the induction of anergy in regulatory cells, and EAU severity increased. The CD4+ regulatory T cells from tolerized rats showed enhanced expression of IL-4 mRNA compared with CD4+ cells from control rats. Increased immunoreactivity for IL-4, IL-10 and TGF-beta was observed in the spleen and lymph nodes of tolerized animals. The results suggest that orchidic tolerance induced by low doses of P343-362 is mediated in part by CD4+ regulatory cells secreting Th2 cytokines.