Chronic relapsing experimental allergic encephalomyelitis in the Lewis rat: studies on immune regulation.

To study immunoregulation of chronic relapsing experimental allergic encephalomyelitis (CR-EAE) in Lewis rats, we adoptively transferred concanavalin A-activated lymph node cells (LNC) or splenocytes, from hind footpad-inoculated donors at the onset (day 11), or recovery (day 16), of the first attack. Popliteal LNC, especially from day 16 donors, provided significant and dose-dependent, but incomplete, protection of recipients from encephalitogenic challenge; maximal mean delay in EAE onset was 10 days later than controls, with subsequent paralysis reduced more than 6-fold. In contrast, particularly from day 11 donors, superficial inguinal LNC recipients developed actively induced disease of normal severity up to 4 days earlier than CR-EAE controls. Furthermore day 11 EAE splenocytes, but not day 16 ones, adoptively transferred disease into 50-88% of naive recipients. In separate studies, we demonstrated unresponsiveness to active induction of disease in all rats re-challenged during stable late remission, as well as in a minority of animals pretreated with antigen in incomplete Freund's adjuvant. These results suggest an organ-dependent and time-dependent balance between effector and suppressor populations in the model.

Syngeneic graft-versus-host disease induced by cyclosporine--a reappraisal.

Cyclosporine-induced graft-versus-host disease has been described in lethally irradiated rats and mice following syngeneic bone marrow reconstitution. To further study this apparently CsA-restricted phenomenon, we followed reported protocols by administering CsA orally at 50 or 100 mg/kg/day to irradiated, syngeneically reconstituted C57B1/6 mice. No clinical evidence of GVHD was observed for more than 8 weeks after CsA discontinuation. Ear biopsies and circulating immunoglobulin levels 2-4 weeks after stopping CsA failed to demonstrate histological or serological evidence of GVHD, respectively, compared with mice allogeneically reconstituted with Balb/c marrow. To further follow a previous report, CsA 50 mg/kg/day orally or 10 mg/kg/day intraperitoneally was given to normal C57B1/6 mice prior to using their spleen or bone marrow cells for reconstitution of lethally irradiated syngeneic mice. Clinical monitoring and histological examination of recipients 2-5 weeks after reconstitution again failed to confirm GVHD. Thus our results were uniformly negative in attempting to reproduce syngeneic GVHD in mice. Existing data on rats and humans are reviewed, showing that syngeneic or autologous GVHD is not CsA-restricted and that the syndrome could be equated to the chronic form of GVHD found in rats and patients after allogeneic bone marrow transplantation.

Enigmatic action of ciclosporine A on the naloxone-precipitated morphine withdrawal syndrome in mice.

Various alterations of the immune system have recently been reported to attenuate the severity of morphine withdrawal. The effect of the immunosuppressive agent ciclosporine A on the naloxone-induced morphine withdrawal syndrome in the chronically dependent mouse was investigated. Ciclosporine A significantly suppressed stereotyped behaviour such as jumping and forepaw treading while wet shakes were potentiated. Withdrawal diarrhoea was diminished as a consequence of a promotive action of ciclosporine A on the intestine. A ciclosporine derivative, which is devoid of immunosuppressive activity, had no influence on withdrawal signs. The attenuating effect of ciclosporine A was observed at a dose of 20 mg/kg i.p., which is not regarded as immunosuppressive in the mouse. It was also effective in animals lacking an intact immune system as a result of a genetic T-cell defect (nude mouse) or after selective ablation by whole body irradiation. Nude mice and irradiated normal mice developed dependence on morphine to the same extent as normal animals, as could be derived from the severity of their withdrawal signs. These results suggest that an intact immune system is not a necessary prerequisite for ciclosporine A to attenuate morphine withdrawal and that its action may be attributable to mechanisms other than immunosuppression. It is possibly a result of a direct effect of ciclosporine A on the central nervous system structures involved in the behavioural expression of the opiate withdrawal syndrome.

Studies on the mechanism of action of cyclosporin A.

The mechanism of cyclosporin A (CS-A), a compound known to act selectively on the immunocompetent lymphocyte, was investigated in a series of in vitro studies. CS-A, provided it was added simultaneously with mitogen, inhibited the incorporation of tritiated uridine and thymidine into mouse spleen cells and human peripheral blood lymphocytes. Addition of CS-A 48 h after onset of culture did not affect cell division, indicating that it acted at an early stage of lymphocyte stimulation, exerted no inhibitory effect on lymphoblasts and did not possess anti-mitotic activity. It was further shown that CS-A was not lymphotoxic and that its effect was reversible, because suppressed spleen cells recovered their proliferative capacity after a 24 h elution period. Inhibition of PFC in the Mishell-Dutton assay provides evidence of an anti-T helper cell action of CS-A.

Immunosuppressive effect of cyclosporin A in two lymphocyte transfer models in rats: comparison of in vivo and in vitro treatment.

The immunosuppressive effect of CS-A was first studied in the assay for local GvHR. 3 X 10(6) viable spleen cells from LEW rats were injected into one foot pad of LEW X BN hybrids and both PLN were weighed 7 days later. Treatment of the recipients with 3 doses of 50 mg/kg/day of CS-A suppressed this local GvHR. The effect was more pronounced when treatment started at the time of cell transfer rather than a few days before peak response. In vitro incubation of the cellular inoculum with CS-A also prevented local GvHR. Histology of the PLN confirmed the quantitative results expressed by the PLN index. CS-A was further investigated in the EAE model in LEW rats. It protected rats sensitised with spinal cord emulsified in complete Freund's adjuvant for as long as they were treated with CS-A. Treatment delayed until after the appearance of EAE also markedly improved their condition. Oral treatment of recipients with 50 mg/kg/day CS-A prevented the development of adoptive EAE following the transfer of lymphoid cells conditioned in vitro. The presence of 0.1-1.0 microgram CS-A in the medium of the sensitised lymphoid cells also inhibited the adoptive transfer of EAE. Finally, if the cells for the adoptive transfer were derived from CS-A-treated sensitised donors, they failed to induce EAE. Histological examination supported the symptomatic findings.

Immunosuppression by cyclosporin A of experimental allergic encephalomyelitis.

Cyclosporin A (CsA), an immunosuppressant which acts selectively on antigen-responding T cells, was tried in the treatment of experimental allergic encephalomyelitis (EAE). The drug was highly effective in preventing the appearance of clinical and pathological signs of EAE in rats, guinea pigs and monkeys. Treatment of the established disease also reduced the incidence and severity of symptoms, and significantly reduced the number of inflammatory lesions in the central nervous system.

Mechanism of action of cyclosporin A and rationale for use in nephrotic syndrome.

Cyclosporin A (CyA, Sandimmun) is the forerunner of a new generation of immunosuppressive drugs. It is highly effective in both antibody- and cell-mediated immunity and in inhibiting chronic inflammatory reactions. Cyclosporin A is, therefore, widely used to prevent rejection in clinical organ transplantation and appears to be very promising in the treatment of several autoimmune diseases. Cyclosporin A is not only effective when given at the time of sensitization (prevention of disease), but also when administered therapeutically during an immune response, such as during the active course of an autoimmune disease. The most important aspect of its immunosuppressive mechanism is the inhibition of lymphokine production secreted by activated T cells. The pharmacological effects of CyA are rapid in onset, dose-dependent and often quickly reversible when treatment is stopped.

The mode of action of immunosuppressive drugs.

The immunosuppression first introduced in the 1950s acted indiscriminately, blocking or damaging all the cells that happened to be in mytosis. The toxic side effects were usually so severe that the overall results were not considered satisfactory. The major drawback to the commonly used combination of steroids and cytotoxic drugs is the high risk of overwhelming infections. The next step was the development of lymphocytotoxic drugs or procedures which were restricted to the elimination of the immunocompetent cells. This was achieved by the use of total lymphoid irradiation, thoracic duct cannulation, antilymphocyte globulin, L-asparaginase and steroids. Steroids not only intervene at many points of the immune response, but they also possess a remarkable anti-inflammatory potency. The current or third stage is that of immunopharmacology, which is characterized by selective immunoregulation using compounds or methods that specifically modulate defined subpopulations of immunocompetent cells. Ciclosporin is the first drug that fulfilled these requirements to some extent and that has proved of permanent clinical value. The new technology of monoclonals has allowed the production of highly specific antibodies directed toward lymphocyte subsets. The modulation of lymphokines is another potential approach for both immunosuppression and immunostimulation. The final phase of immunosuppression will be the induction of antigen-specific depression of allograft reactivity. Classical transplantation tolerance has been induced in a developing immune system, but it is virtually impossible to achieve in a fully developed immune system.

Molecular mechanisms of immunosuppressive agents.

Recent data on the molecular mechanism of some immunosuppressive drugs provide strong support for the fascinating postulate that CSA and FK506 work by binding to immunophilins and then, as a drug-immunophilin complex, inhibiting the calcium-activated protein phosphatase, calcineurin. This inhibition could result in an altered modification pattern of the cytoplasmic components of transcription factors, thereby disturbing their nuclear translocation, which is a prerequisite for proper IL-2 transcription. It looks as if, with the immunosuppressive microbial metabolites as molecular probes, the pieces of this complex signal transduction puzzle are starting to fit together! Once the details of the chain of events along the T-cell signaling pathways are known, the molecular structures involved will provide new tools to be used in the search for and the rational design of new and improved therapeutic agents.