Inhibition of macrophage activation and tumor cell cytolysis by cyclosporin-A

Cyclosporin A inhibits nitric oxide production by L929 cells in response to tumor necrosis factor and interferon-gamma

We recently reported that tumor necrosis factor (TNF) induced the production of nitric oxide (NO) by TNF-sensitive, but not-resistant, tumor cells. Paradoxically, NO thus produced does not appear to be involved in the mechanism of TNF-mediated cytotoxicity as inhibitors of NO production and NO scavengers did not block cytotoxicity. Because the immunosuppressive drug cyclosporin A (CsA) inhibits several types of immune-mediated killing, we were interested in what effect CsA would have on TNF-mediated cytotoxicity as well as NO production. Treatment with CsA had no effect on the sensitivity L929 cells to TNF-mediated cytotoxicity, either in the presence or absence of interferon-gamma (IFN-gamma). In the presence of IFN-gamma alone, L929 cells were slightly less sensitive to the cytotoxic effects of TNF. In contrast to the effect on TNF-mediated cytotoxicity, CsA treatment had a profound effect on the ability of these cells to produce NO in response to TNF and IFN-gamma. Cells treated with CsA produced 75% less NO than did their untreated controls. Inhibition of calmodulin-dependent calcineurin-like phosphatases is one mechanism by which CsA may exert its effects. Therefore, we tested the effect of EGTA, which inhibits calcineurin by chelating calcium, on NO production and found that EGTA treatment resulted in a 15% decrease in the amount of NO produced. In addition, cells treated with the calmodulin antagonist W-13 produced 79% less NO than their untreated controls. Therefore, these results provide further evidence that NO produced by TNF-sensitive cells is not involved in the mechanism of TNF-mediated cytotoxicity because reduction of NO production by CsA has no effect on TNF-mediated killing of these same cells.

Cyclosporin A protects pancreatic islet cells from nitric oxide-dependent macrophage cytotoxicity

It has been shown earlier in an in-vitro model of inflammatory islet cell death that activated macrophages lyse islet cells via the release of nitric oxide. Here we report that cyclosporin A suppresses macrophage cytotoxicity. Control experiments showed that the immunosuppressive drug does not improve the defences of islet cells against nitric oxide but inhibits the release of nitric oxide from LPS-stimulated macrophages. This property of cyclosporin A may contribute to the preservation of beta cell function seen in cyclosporin A-treated patients with recent onset type I diabetes.

Effects of an immunosuppressant, FK506, on interleukin 1 alpha production by human macrophages and a macrophage-like cell line, U937

A recently discovered immunosuppressive agent, FK506, has been shown to be effective primarily as an inhibitor of T cell responses in vitro, but little is known about its effects on accessory cell function. This study was undertaken to determine the effect of FK506 on interleukin 1 (IL-1) production by macrophages, by using a sensitive and specific enzyme-linked immunosorbent assay. FK506 partially suppressed IL-1 alpha release, from macrophage-like U937 cells stimulated with phorbol myristate acetate and from human monocytes and alveolar macrophages activated with lipopolysaccharide, in a dose-dependent manner. Moreover, it was indicated that FK506 suppressed not only IL-1 release but also IL-1 synthesis itself, by measurement of cell-associated IL-1 alpha of U937 cells. The optimal concentrations of FK506 for suppressing IL-1 alpha did not affect cell viability or proliferation, and were 10- to 100-fold lower than those of cyclosporin A. It is concluded that FK506 affects macrophage physiology, suppressing IL-1 alpha production significantly. Thus, FK506 has the potency to act on non-T cells and the effect on macrophages may play an additional role in preventing graft rejection.

Influence of host defenses on the hepatic colonization of B16F10 melanoma cells

To investigate the significance of host immunity in metastasis we have simultaneously evaluated metastatic development and the tumoricidal action of host defenses in an experimental system for liver metastasis which involves the intrasplenic injection of B16F10 melanoma cells in syngeneic mice. In addition, three experimental groups were treated with immunosuppressive doses of cyclosporin A (CsA) during the following periods of the malignant process: 1st-5th days, 1st-12th days and 7th-12th days. Analysis of cytolytic effects of macrophages, NK cells and T-lymphocytes on tumor cells reveals a decay in antitumor immunity from the 7th day to the 12th day and a marked resistance of B16F10 melanoma cells derived from hepatic metastases to T-lymphocytes and NK cells. The 1st-5th day CsA treatment of tumor-bearing mice produced a reduction in both T-lymphocyte and macrophage reactions against tumor cells and a significant increase in the 7th day micrometastasis incidence in the liver. Once micrometastases have been established the CsA-treatment suppression on the 5th day allows the tumor growth rate in these mice to become the same as in controls. However, the 7th-12th day CsA treatment produces a clear inhibitory effect on focal metastatic development which may correspond to the in vitro antiproliferative effect of CsA, detected on cultured B16F10 melanoma cells.

Action of cyclosporine on mitochondrial calcium fluxes

Cyclosporine (Cys A) is a potent immunosuppressor used to reduce rejection in transplantation surgery. We studied its action upon mitochondrial functions: oxidative phosphorylation and Ca2+ movements through mitochondrial membrane. We show that Cys A exhibits an inhibitory effect upon mitochondrial respiration. This result is in good agreement with previous works and may be correlated with Cys A toxicity. The action of cyclosporine on calcium fluxes is more pronounced. Indeed it blocks mitochondrial calcium efflux and allows mitochondria to accumulate a large amount of calcium. If this effect occurs in the cell, it would induce a Ca2+ decrease in cytosol. This action might be correlated with the inhibitory effect of Cys A upon the mitogenic stimulation of T lymphocytes.

Induction by immunomodulatory agents of a macrophage antigen recognized by monoclonal antibody 158.2 and correlation with macrophage function

MA158.2, a rat monoclonal antibody with binding specificity for cells of the monocyte-macrophage lineage, reacts with an antigen (158.2) whose expression is enhanced on mononuclear cells activated to the tumoricidal phenotype by treatment with lymphokine supernatant containing macrophage activating factor (MAF). The functional relevance of enhanced expression of this antigen has been examined in mouse peritoneal macrophages treated with a variety of immunomodulatory agents and assayed for augmented macrophage-mediated defense reactions, including O-2 production, microbicidal, and tumoricidal activity. An interferon-gamma (IFN-gamma) preparation produced by recombinant DNA technology induced a dose-dependent increase in expression of the 158.2 antigen in inflammatory macrophages which was accompanied by acquisition of microbicidal activity against Listeria monocytogenes. However, these cells did not express tumoricidal activity and induction of this property required concomitant exposure to lipopolysaccharide (LPS). Similar results were obtained using macrophages elicited with pyran copolymer. Exposure to LPS alone induced enhanced expression of antigen 158.2 but did not elicit microbicidal activity. Macrophages challenged with IFN-alpha, IFN-beta, MDP, and bestatin did not exhibit increased 158.2 and also failed to acquire tumoricidal activity when treated concomitantly with LPS. Collectively, these data indicate that the MA 158.2 antibody recognizes an antigen expressed by macrophage populations displaying the so-called primed phenotype in which microbicidal activity is expressed but in which induction of tumoricidal activity requires the addition of a second signal such as LPS.