Lymphocyte-mediated macrophage apoptosis during IL-12 stimulation.

In contrast to the well known immunostimulatory roles of IL-12, little has been known about its immunosuppressive roles. In the present study, IL-12-activated lymphocyte-mediated macrophage apoptosis was investigated by employing murine lymphocyte/macrophage cocultures. IL-12-activated lymphocytes and their culture supernatants induced an inducible nitric oxide synthase (iNOS)-mediated nitric oxide (NO) synthesis in macrophages. The NO synthesis was markedly inhibited by blocking antibodies to IFN-γ and TNF-α, suggesting the key role of these lymphocyte cytokines in mediating the NO synthesis. The endogenously produced NO inhibited macrophage proliferation, and induced apoptosis in concordance with the accumulation of p53, phosphatase and tensin homologue deleted on chromosome 10 (PTEN) and DR5, and the activation of caspase-3, processes that were inhibited by N(G)-monomethyl-l-arginine, aminoguanidine (NO synthase inhibitors) and 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl 3-oxide (an NO scavenger). These results were further supported by the findings obtained from the experiments employing IFN-γ-knockout and iNOS-knockout mice. Our study demonstrated a novel, non-contact-dependent mechanism of macrophage suppression by IL-12-activated lymphocytes: induction of growth inhibition and apoptosis of macrophages due to endogenous NO synthesis induced by cytokines secreted from IL-12-activated lymphocytes.

Glutamine protects mice from acute graft-versus-host disease (aGVHD).

Despite current immunosuppressive therapies, acute graft-versus-host disease (aGVHD) is a major cause of morbidity and mortality in allogeneic hematopoietic stem cell transplantation (HSCT). In the present study, therapeutic effects of intraperitoneal glutamine (Gln) administration (1g/kg/day) in a mouse aGVHD model were evaluated. Gln administration significantly inhibited the GVHD-induced inflammation and tissue injury in the intestine, liver, skin and spleen. Gln therapy improved the score of clinical evidence of aGVHD and prolonged the median survival of aGVHD mice. Gln administration in aGVHD mice increased the fraction of Foxp3+/CD4+/CD25+ cells in the blood measured on day 7, and decreased the serum levels of tumor necrosis factor-α measured on days 7, 14 and 21 after aGVHD induction. These results demonstrated that Gln administration may be useful in protecting the host from aGVHD.

Rosiglitazone prevents graft-versus-host disease (GVHD).

The effect of rosiglitazone, an agonist of peroxisome proliferator-activated receptor-γ (PPARγ), was investigated in a mouse parent-to-F1 GVHD model. Rosiglitazone inhibited mixed lymphocyte reactions, inducing enhanced apoptosis in CD4+, CD8+, and B220+ cells, but not in NK1.1+, Mac-1+, CD4+/CD25+ and CD3+/NK1.1+ cells. Rosiglitazone administration prevented GVHD in the liver, skin, spleen and intestine. Rosiglitazone inhibited GVHD-induced increases in serum levels of tumor necrosis factor-alpha, interferon-gamma, interleukin (IL)-6, and IL-12, and the GVHD-induced decreases in transforming growth factor-beta and IL-10. Immunophenotyping of splenic leukocytes demonstrated that while rosiglitazone treatment increased the population percentages of both donor and host CD4+/CD25+ and CD3+/NK1.1+ cells, the treatment resulted in lower fractions of both donor and host CD8+ cells. Rosiglitazone inhibited the GVHD-induced decreases in the expression of phosphatase and tensin homologue deleted on chromosome 10 (PTEN), as well as the GVHD-induced increase in the splenic p-Akt and nuclear factor-kappa B expression. These results indicate that rosiglitazone and PPARγ activation may be useful in protecting the host from GVHD.

Use of curcumin to decrease nitric oxide production during the induction of antitumor responses by IL-2.

Nitric oxide (NO) synthesis is strongly induced during interleukin (IL)-2 treatment of mice and humans. Although this free radical can act as a cytotoxic effector molecule against cancer cells, immunosuppressive effects have also been suggested. We evaluated the effects of curcumin on IL-2-induced NO synthesis and IL-2-induced antitumor responses in a mouse ascites tumor model. Curcumin inhibited inducible nitric oxide synthase (iNOS) expression and NO production, and thereby enhanced the proliferation and cytotoxic activity of cocultured lymphocytes and macrophages during IL-2 stimulation which we earlier established as an in vitro model of IL-2-induced NO synthesis. Curcumin also decreased apoptosis of cocultured lymphocytes and macrophages during IL-2 stimulation. In contrast, the curcumin-induced changes in proliferation and apoptosis were not observed in cultures of lymphocytes alone, macrophages alone, and cocultured lymphocytes/iNOS-knock out macrophages, all of which produced little nitrite during IL-2 stimulation. In conjunction with IL-2 treatment, oral curcumin administration significantly inhibited IL-2 therapy-induced urinary nitrite/nitrate excretion and iNOS expression of tumor tissues, and further increased the IL-2 therapy-induced prolongation of survival in a murine Meth-A ascites tumor model. Curcumin may be useful as an adjunct to increase the antitumor activity of IL-2 therapy.