Autocrine stimulation of interleukin-1 alpha and transforming growth factor alpha production in human keratinocytes and its antagonism by glucocorticoids.

Interleukin-1 (IL-1) and transforming growth factor alpha (TGF alpha) mRNA expression was analyzed in cultured normal human keratinocytes. Keratinocytes constititively express IL-1 mRNA when cultured in keratinocyte growth medium but not in Dulbecco's minimal essential medium containing fetal bovine serum, in which the cells differentiate. The predominant form of IL-1 expressed by keratinocytes is IL-1 alpha. Addition of IL-1 alpha to keratinocytes increased IL-1 alpha and TGF alpha mRNA expression in a dose-dependent manner. TGF alpha induced a similar increase in IL-1 alpha and TGF alpha mRNA in keratinocytes. Hydrocortisone decreased the expression of both IL-1 alpha and TGF alpha mRNA in keratinocytes. These findings document an autocrine mechanism by which IL-1 alpha and TGF alpha can stimulate the proliferation of keratinocytes in the skin. It is proposed that this autocrine loop may be hyperactive in psoriasis. Antagonism of the effects of this autocrine loop may be one of the mechanisms by which glucocorticoids exert clinically useful effects in psoriasis and other diseases of the skin.

Structure-activity relationships for inhibition of inosine monophosphate dehydrogenase by nuclear variants of mycophenolic acid.

Structure-activity relationships in the region of the phthalide ring of the inosine monophosphate dehydrogenase inhibitor mycophenolic acid have been explored. Replacement of the lactone ring with other cyclic moieties resulted in loss of potency, especially for larger groups. Replacement of the ring by acyclic substituents also indicated a strong sensitivity to steric bulk. A phenolic hydroxyl group, with an adjacent hydrogen bond acceptor, was found to be essential for high potency. The aromatic methyl group was essential for activity; the methoxyl group could be replaced by ethyl to give a compound with 2-4 times the potency of mycophenolic acid in vitro and in vivo.

Facilitation of specific tolerance induction in adult mice by RS-61443.

RS-61443 is an immunosuppressive agent that facilitates pancreatic islet allograft acceptance in two mouse strain combinations (BALB/c----CBA and C57Bl/6J----BALB/c). A remarkable feature of this agent is its ability to facilitate long-term graft acceptance after a short (30 days) period of treatment; following withdrawal of the agent 40-70% of islet allografts are maintained for an indefinite period. This long-term graft acceptance has been shown to result from specific tolerance induction in the recipient animal. The state of specific tolerance is an active rather than a passive form of tolerance, such as clonal deletion or anergy. Active tolerance induction is cyclosporine-sensitive, although cyclosporine enhances graft acceptance when used in combination therapy with RS-61443, this agent inhibits tolerance development under the influence of RS-61443.

RS-61443--a new, potent immunosuppressive agent.

The immunosuppressive activity of RS-61443, a semisynthetic derivative of mycophenolic acid, was examined in 33 canine renal allografts. Initial studies established that triple therapy consisting of 20 mg/kg RS-61443 in combination with 5 mg/kg cyclosporine and 0.1 mg/kg methylprednisolone was the optimal combination to prevent graft rejection. The median survival time was 8.1 +/- 1.2 days in dogs without treatment (n = 5), 8.5 +/- 1.7 days in the treatment control group (CsA 5 mg/kg, MP 0.1 mg/kg; n = 6), 36.0 +/- 9.6 days with RS-61443 monotherapy (40 mg/kg; n = 6); and 122.4 +/- 38.75 days with triple therapy (n = 16). Graft prolongation was statistically significant when compared with controls (P less than 0.05 and 0.002, respectively). Six recipients in the triple therapy group survived over 150 days without major adverse effects. Long-term administration of RS-61443 (20 mg/kg/day) did not cause nephrotoxicity, hematotoxicity, or hepatotoxicity, with the exception of a slight elevation of the alkaline phosphatase levels. Gastrointestinal symptoms including gastritis, diarrhea, and anorexia were common, especially under 40 mg/kg RS-61443 monotherapy, and appeared to be dose-related. Despite its immunosuppressive activity, an increased susceptibility to bacterial or viral infections was not observed. Histological studies of the kidney grafts revealed slight interstitial cell infiltration without vascular or glomerular damage.

Insulin-like growth factor-1 increases the mitogenic response of human peripheral blood lymphocytes to phytohemagglutinin.

Receptors for insulin and insulin-like growth factor-1 (IGF-1) have been demonstrated on activated T-lymphocytes. The question is whether receptors for insulin or IGF-1 have any function in these cells. In this study we demonstrate that the concentration of IGF-1 in commercial samples of fetal calf serum is about 70 times that of insulin. Moreover, antibodies binding IGF-1 reduce responses of human peripheral blood mononuclear cells to PHA by about 50%, whereas antibodies to insulin have no demonstrable effect. These observations suggest that binding of IGF-1 to specific receptors contributes to the proliferative responses of activated T-lymphocytes.

IL-6 is the principal factor produced by synovia of patients with rheumatoid arthritis that induces B-lymphocytes to secrete immunoglobulins.

First, IL-6 is produced by synovial tissue of patients with rheumatoid arthritis (RA) and is the principal mediator produced by that tissue inducing differentiation of B-lymphocytes into antibody-forming cells. The Leu-1+ subset of B-lymphocytes is induced by IL-6 to secrete rheumatoid factor (IgM with anti-Fc gamma specificity). Second, the main cell types producing IL-6 in cells dissociated from RA synovial tissue are mononuclear leukocytes. Connective tissue type cells (synoviocytes) cultured from RA synovial tissue produce IL-6 in response to IL-1 beta, and IL-6 formation is increased by TGF-beta. Glucocorticoids strongly inhibit and PGE2 slightly inhibits IL-1-induced IL-6 mRNA expression in synoviocytes. Production of IL-6 increases when undissociated RA synovial tissue is maintained in culture, thus suggesting release from inhibition by a factor or factors not yet identified. Third, the major known local effect of IL-6 in RA synovial tissue is the augmentation of antibody formation and the major known systemic effect is the induction of the synthesis by the liver of acute-phase proteins, especially C-reactive protein. Levels of circulating C-reactive protein are reported to decrease in RA patients receiving long-acting antirheumatic drugs, which would be consistent with the interpretation that immature monocyte-derived macrophages are major producers of IL-6 in these patients.

[Present and future of immunosuppressive therapy]. / Presente y futuro de la terapia inmunosupresora.

Immunosuppressive drugs make possible the acceptance of organ allografts among individuals with differences in Major Histocompatibility Antigens (HLA). Transplantation of vital organs prolongs the survival of patients with terminal diseases, and this procedure has become a routine practice in the clinic, mainly because of advances in immunosuppressive therapy. Some immunosuppressive drugs, such as glucocorticosteroids and azathioprine, have been used for the past 30 years. More recently, newly discovered agents with a better ratio of efficacy to toxicity have been added to the armamentarium of anti-rejection therapies. Progress in understanding T cell activation in response to alloantigens has contributed to the development of new and more selective strategies to control the immune response and prevent acute rejection. The use of drugs in combination, with or without monoclonal antibodies, has also improved the efficacy and reduced the toxicity of immunosuppressive therapies. The new agents include drugs that interfere with calcineurin, inhibitors of de novo purine biosynthesis, kinase inhibitors, as well as monoclonal antibodies that block activation signals on the surface of T cells or co-stimulatory signals between T cells and antigen-presenting cells. In this review the modes of action of commonly used immunosuppressive drugs are described. Successful new strategies are also being developed to establish tolerance to allografts in rodents and non-human primates. The progress in these approaches, although still in the experimental stages, offers promising alternatives for these patients in the future. Treatment protocols using combinations of drugs with antibodies that might produce tolerance in humans are also discussed.