A potent immunosuppressive activity was found in the culture broth of the fungus Isaria sinclairii (ATCC 24400). The metabolite, ISP-I ((2JS,3^,4^)-(j&)-2-amino-3,4-dihydroxy-2-hydroxymethyl-14-oxoeicos-6-enoic acid, myriocin = thermozymocidin) suppressed the proliferation of lymphocytes in mouse allogeneic mixed lymphocyte reaction, but had no effect on the growth of humantumor cell lines. It also suppressed the appearance of plaque-forming cells in response to sheep red blood cells and the generation of allo-reactive cytotoxic T lymphocytes in mice after intraperitoneal or oral administration.The metabolite was 10-to 100-fold more potent than cyclosporin A as an immunosuppressiveagent of the immuneresponse in vitro and in vivo, and appears to be a candidate for clinical application as a powerful immunosuppressant.

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A new compound with an immunosuppressive property was purified from culture filtrates of Isaria sinclairii and was chemically modified to FTY720. Rat spleen cells incubated with FTY720 demonstrated features characteristic of apoptosis--such as the absence of surface microvilli, chromatin condensation, and the formation of apoptotic bodies--by electron microscopy, and genemic DNA fragmentation by agarose gel electrophoresis. When FTY720 was administered in liver-allografted rats at a dose of 0.5 mg/kg from day 1 to day 14 after transplantation, the recipients survived significantly longer than the control group. Pretransplant treatment with 5 mg/kg of FTY720 one day before and on the day of grafting induced a remarkable prolongation of recipient survival, and three of 10 recipients survived for longer than 50 days. Furthermore, administration of FTY720 at 5 mg/kg on days 3 and day 4 after grafting also prolonged survival. In canine kidney allografting, a pretransplant 2-day course of FTY720 at 5 mg/kg prolonged graft survival. Daily administration of FTY720 in combination with CsA resulted in a significant prolongation of graft survival in a synergistic manner. In addition, FTY720 appeared to be nontoxic in canine recipients. These results demonstrated that FTY720, having a unique mechanism of action, induces long-term graft acceptance in rat and dog allotransplantation.

A series of 2-substituted 2-aminopropane-1,3-diols was synthesized and evaluated for their lymphocyte-decreasing effect and immunosuppressive effect on rat skin allograft. A phenyl ring was introduced into the alkyl chain of the lead compound 3, which is an immunosuppressive agent structurally simplified from myriocin (1, ISP-I) via compound 2. The potency of the various compounds was dependent upon the position of the phenyl ring within the alkyl side chain. The most suitable length between the quaternary carbon atom and the phenyl ring was two carbon atoms. 2-Substituted 2-aminoethanols were successively synthesized and evaluated for their T-cell-decreasing effect and immunosuppressive effect using a popliteal lymph node gain assay in rats. The absolute configuration at the quaternary carbon affected the activity, and the (pro-S)-hydroxymethyl group of compound 6 was essential for potent immunosuppressive activity. Favorable substituents for the (pro-R)-hydroxymethyl group of 6 were hydroxyalkyl (hydroxyethyl and hydroxypropyl) or lower alkyl (methyl and ethyl) groups. 2-Amino-2-[2-(4-octylphenyl)ethyl]propane-1,3-diol hydrochloride (6, FTY720) was found to possess considerable activity and is expected to be useful as an immunosuppressive drug for organ transplantation.

Psychiatric disorders such as schizophrenia and major depressive disorder were thought to be caused by neurotransmitter abnormalities. Patients with these disorders often experience relapse and remission; however the underlying molecular mechanisms of relapse and remission still remain unclear. Recent advanced immunological analyses have revealed that M1/M2 polarization of macrophages plays an important role in controlling the balance between promotion and suppression in inflammation. Microglial cells share certain characteristics with macrophages and contribute to immune-surveillance in the central nervous system (CNS). In this review, we summarize immunoregulatory functions of microglia and discuss a possible role of microglial M1/M2 polarization in relapse and remission of psychiatric disorders and diseases. M1 polarized microglia can produce pro-inflammatory cytokines, reactive oxygen species, and nitric oxide, suggesting that these molecules contribute to dysfunction of neural network in the CNS. Alternatively, M2 polarized microglia express cytokines and receptors that are implicated in inhibiting inflammation and restoring homeostasis. Based on these aspects, we propose a possibility that M1 and M2 microglia are related to relapse and remission, respectively in psychiatric disorders and diseases. Consequently, a target molecule skewing M2 polarization of microglia may provide beneficial therapies for these disorders and diseases in the CNS.

Dendritic cells (DCs) and lymphocytes are known to show a migratory response to the phospholipid mediator, sphingosine 1-phosphate (S1P). However, it is unclear whether the same S1P receptor subtype mediates the migration of lymphocytes and DCs toward S1P. In this study, we investigated the involvement of S1P receptor subtypes in S1P-induced migration of CD4 T cells and bone marrow-derived DCs in mice. A potent S1P receptor agonist, the (S)-enantiomer of FTY720-phosphate [(S)-FTY720-P], at 0.1 nM or higher and a selective S1P receptor type 1 (S1P1) agonist, SEW2871, at 0.1 μM or higher induced a dose-dependent down-regulation of S1P1. The pretreatment with these compounds resulted in a significant inhibition of mouse CD4 T cell migration toward S1P. Thus, it is revealed that CD4 T cell migration toward S1P is highly dependent on S1P1. Mature DCs, when compared with CD4 T cells or immature DCs, expressed a relatively higher level of S1P3 mRNA. S1P at 10–1000 nM induced a marked migration and significantly enhanced the endocytosis of FITC-dextran in mature but not immature DCs. Pretreatment with (S)-FTY720-P at 0.1 μM or higher resulted in a significant inhibition of S1P-induced migration and endocytosis in mature DCs, whereas SEW2871 up to 100 μM did not show any clear effect. Moreover, we found that S1P-induced migration and endocytosis were at an extremely low level in mature DCs prepared from S1P3-knockout mice. These results indicate that S1P regulates migration and endocytosis of murine mature DCs via S1P3 but not S1P1.

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