IL-3, IL-4, and IL-6 enhance IFN-gamma-dependent bone marrow natural suppressor activity

Decreasing endogenous glucocorticoids alters the ability of bone marrow cells to produce nitric oxide in response to stimulating agents

Glucocorticoids (GC) are essential for the body to maintain homeostasis. Patients with adrenal insufficiencies suffer from numerous health related problems including increased mortality due to sepsis. Here, we examine bone marrow (BM) cells from mice with adrenal insufficiency for their ability to produce nitric oxide (NO). Mice were injected with metyrapone (MR), an agent that selectively blocks glucocorticoid synthesis. BM cells were removed and tested for NO production. The stimulating agents LPS, TNF-alpha, IL-1beta, and IL-4 were all able to synergize with IFN-gamma, stimulating large concentrations of NO compared to normal mice. An important finding is that BM from injected mice produces NO in response to LPS alone, while normal BM cells do not. Experiments with anti IFN-gamma antibody demonstrate that, in MR injected mice, LPS alone stimulated sufficient quantities of IFN-gamma necessary for NO production. Our results demonstrate that reducing GCs alters regulation of NO production by BM cells at several levels.

Prednisolone inhibits LPS-induced bone marrow suppressor cell activity in vitro but not in vivo

Glucocorticoids are used clinically to treat a variety of inflammatory diseases including endotoxemia. We hypothesized that injecting mice with the steroid prednisolone (pred) would mitigate the enhanced bone marrow (BM) natural suppressor (NS) cell activity that occurs in mice after receiving an injection of lipopolysaccharide (LPS). In vitro, prednisolone blocked the ability of NS cells to produce the immunosuppressive molecule nitric oxide (NO) and also the ability to suppress T cell proliferation. Prednisolone acted both indirectly, by blocking synthesis of cytokines necessary for NS cell activation, and also directly on NS cells, by blocking production of NO. In vivo, variable results were obtained. Prednisolone at 20 microg/gm did decrease NS activity when injected into normal mice. However, when mice were injected with both LPS and prednisolone (0.2 or 20 microg/gm), a large increase in BM NS activity was observed. The increase was evident in both the ability of the BM cells to suppress T cell proliferation and to produce NO. The data show that, in vivo, the steroid prednisolone in conjunction with the inflammatory compound LPS act to enhance BM NS activity.

Kinetics of interferon-gamma secretion and its regulatory factors in the early phase of acute graft-versus-host disease

Increased serum levels of interferon-gamma (IFN-gamma) have been observed in acute graft-versus-host disease (GVHD). Recent in vitro studies have demonstrated that interleukin-12 (IL-12) and interleukin-18 (IL-18) synergistically up-regulate IFN-gamma secretion. In this communication, we investigated the factors relevant to IFN-gamma secretion in acute GVHD. A murine model of acute GVHD was established by injecting donor spleen cells into severe combined immunodeficiency (SCID) mice. A series of specimens, including sera, livers and spleens derived from the GVHD mice, were investigated with histological examination, enzyme-linked immunosorbent assay (ELISA), flow cytometry, and semiquantitative reverse transcription-polymerase chain reaction (RT-PCR). IFN-gamma secretion increased in serum 3 days after spleen cell transfer, peaked on day 7, and then gradually decreased close to the baseline level by day 35. A synchronized increase of activated T cells and mRNA expression of IL-12, IL-18 and their respective receptors was observed after spleen cell transfer. However, only the kinetic expression pattern of IL-12 receptor (IL-12R) beta2 chains was closely correlated with that of IFN-gamma, while IL-12 dropped to the baseline level earlier than IFN-gamma. Therefore, IFN-gamma expression in the early phase of acute GVHD is a mono-peak and self-restricted pattern. Its secretion is closely related with T-cell activation, the presence of IL-12, IL-18 and their respective receptors. However, the limiting factors for IFN-gamma secretion seem to be IL-12 and IL-12R beta2 chains.

Tumor growth inhibitory and natural suppressor activities of murine bone marrow cells: a comparative study

The murine bone marrow (BM) cells having a certain phenotypic similarity to null natural suppressor (NS) cells have been previously established to be able to inhibit in vitro leukemic cell growth in a genetically unrestricted manner. In this study we found that the treatment of normal (C57BL/6 x DBA)F1 BM cells with a lysosomotropic agent, L-leucine methyl ester (LME), largely abrogated their ability to reduce both P815 mastocytoma and L1210 lymphoma cell proliferation, as well as their NS activity tested for suppression of mitogen (Con A or LPS)-driven spleen cell proliferation. However, after being depleted of the cells binding wheat germ agglutinin (WGA), the BM cells maintained tumor growth-inhibitory activity, while demonstrating no significant NS activity. Moreover, in contrast to T-cell blastogenesis-inhibitory NS activity of BM cells, that was greatly reduced by the addition into the culture of either neutralizing anti-interferon (IFN)-gamma antibody (Ab) or NG-monomethyl-L-arginine, a competitive inhibitor of NO synthase, natural antitumor cytostatic activity of BM cells was not found to be dependent on the presence in medium of IFN-gamma and to be associated with NO production. When incubated at suboptimal numbers with tumor cells on conic, round, and flat well bottoms for 7 h, BM cells provided the most, middle, and least (or no) tumor growth inhibition, respectively, suggesting, thereby, a significance of cell density in cytostatic process. It was also found that the BM cells cultured for 20 h with the medium conditioned by mitogen-preactivated T or B lymphocytes were significantly more suppressive to tumor cell proliferation than the BM cells cultured in medium alone. The potentiation of BM-cell cytostatic activity by T-cell-conditioned medium (CM), but not that by B-cell-CM, was found to be partially reversed by anti-IFN-gamma Ab. Finally, a noticeable tumor growth-inhibitory activity, which could be significantly enhanced upon T-cell-CM, was shown to be also attributable to BM cells from athymic BALB/c mice. Taken together, the results suggest that (1) the tumor growth inhibitory BM cells and the NS BM cells are not identical in their cell compositions, but also differ in their mechanisms of antiproliferative action; (2) a contact cell-to-cell interaction may play a significant role in BM-cell-mediated tumor growth inhibition; (3) the activated lymphocytes, through both IFN-gamma-mediated and IFN-gamma-independent pathways, are able to operatively up-regulate the cytostatic activity of BM cells; and (4) the tumor growth-inhibitory activity exhibited by the normal unmanipulated BM cells, at least in its significant part, may not be a consequence of thymus-dependent immune processes occurring normally in the body.

Regulation of autoimmune diabetes by interleukin 3-dependent bone marrow-derived cells in NOD mice

Interleukin-3 (IL-3), a multilineage colony stimulating factor, has been shown to augment alloreactive bone marrow-derived suppressor cell activity in vivo and in vitro. The present study examined the effect of IL-3 on autoimmune-mediated diabetes in NOD mice. Administration of IL-3 twice weekly starting at 2-4 weeks of age delayed the onset and reduced the overall incidence of diabetes. Bone marrow cells obtained from IL-3-treated NOD mice protected NOD mice from cyclophosphamide-induced diabetes but failed to prevent adoptively transferred diabetes. In vitro culture of bone marrow cells in medium containing IL-3 produced a Thy-1+CD3epsilonloCD4-CD8-CD25- immature T cell clone which prevented cyclophosphamide-induced diabetes. The cloned cells also effectively delayed the development of diabetes induced by transfer of T cells in adult thymectomized, irradiated, bone marrow-reconstituted NOD mice. These results suggest that IL-3 is capable of regulating extrathymic T cell development from the bone marrow and that these cells mediate strong immunoregulatory function.

CD4- CD8- TCR alpha/beta+ suppressor T cells demonstrated in mice 1 day after thermal injury

We have described previously that CD8+ CD11b+ TCR gamma/delta+ type 2 T cells (BA-type 2 T cells) and suppressor macrophages (Sup-Mł) are generated in spleens of mice 3 to 5 days (Sup-Mł) and 4 to 9 days (BA-type 2 T cells) after thermal injury. In the present study, an additional suppressor T cell, characterized as CD3+ CD4- CD8- TCR alpha/beta+ T cells (double negative suppressor T cells, DN Sup-T cells), was demonstrated in mice 1 day after thermal injury. DN Sup-T cells inhibited the proliferation of lymphocytes stimulated with allogeneic cells or a lectin in a mixed lymphocyte reaction, and produced both type 1 and type 2 cytokines (interferon-gamma, interleukin-2, interleukin-4, and interleukin-10) when they were stimulated in vitro with anti-CD3 monoclonal antibody. These results suggest that DN Sup-T cells express phenotypic properties similar to natural suppressor cells and cytokine-producing profiles different from type 1 (Th1 cells and CTLs) and type 2 T cells (Th2 cells and CD8+ type 2 T cells). DN Sup-T cells may play a role on the burn-associated immunosuppression appearing in the acute phase of thermally injured individuals.

The identification of the neonatal NBXFO hybridoma cell and its mediator

The neonatal spleen:myeloma hybridoma cell, NBXFO, with immunosuppressive properties supported rodent hematopoietic colony formation. We identified this hybridoma to be an undifferentiated fibroblast that produced macrophage colony-stimulating factor (M-CSF). The bone marrow cells that grew in the presence of the NBXFO supernate were macrophages and were immunosuppressive towards lymphocytes. Neutralizing anti-M-CSF antibody partially inhibited the actions of the neonatal splenic suppressor cells. Neonatal splenocytes, but not the other parental cell line, FO, induced macrophage colony formation, possessed surface-associated M-CSF, and possessed M-CSF-specific transcripts. Therefore, we believe that the M-CSF-producing phenotype was contributed by a fibroblastic stromal cell and that these stromal cells could be responsible for the in situ generation of neonatal splenic suppressor cells.

Effects of 15-deoxyspergualin on proliferative responses and cytokine gene expression in vitro

15-deoxyspergualin (DSG)-treated BALB/c spleen cells showed increased spontaneous proliferation and increased alloreactive mixed lymphocyte reactions (MLRs) when a 3-h treatment was carried out. However, when spleen cells were treated with DSG for 5 days without washing out DSG, decreased spontaneous proliferation was observed, although alloreactive MLRs against C3H/He and C57BL/6 alloantigens were increased. In contrast, cyclosporin A (CsA) induced markedly decreased alloreactive MLRs. Decreased concanavalin A (Con A)- and pokeweed mitogen (PWM)-induced responses were observed in spleen cells treated with DSG for 3 h; whereas increased phytohemagglutinin (PHA)-induced responses were observed. On the other hand, increased Con A- and PHA-induced responses were observed in spleen cells treated with DSG for 2 days, whereas PWM-induced responses were decreased. CsA-treatment induced markedly decreased mitogen-induced responses. These results suggest that the immunosuppressive mechanism of DSG differs from that of CsA. Reverse transcriptase-polymerase chain reaction (RT-PCR) method showed that interleukin 1 beta (IL-1 beta), IL-2, IL-3, IL-4, IL-5, and leukemia inhibitory factor (LIF) mRNA expression in DSG-treated spleen cells were increased by Con A stimulation, thus indicating that DSG modulates cytokine gene expression and inducing immunosuppressive mechanisms different from CsA.

LPS activation of bone marrow natural suppressor cells

Lipopolysaccharide (LPS) from Salmonella typhosa was injected into C57B1/6 mice and the effect on bone marrow (BM) natural suppressor (NS) cell activity was examined. It was shown that injection of LPS, as low as 0.01 microgram/g body weight, could enhance BM NS activity. The enhanced activity was apparent 24 hr postinjection, and returned to normal by Day 5. It was necessary to show that the enhanced suppression displayed characteristics of NS cells. The suppressor cell is Thy negative and can be found in low density Percoll fractions. Suppression was dependent upon interferon-gamma and could be augmented by lymphokines that were contained in the supernatant of TH2 helper cell. The data suggest that BM NS activity may be influenced in vivo during gram-negative sepsis.

Cytokine regulation of bone marrow natural suppressor cell activity in the suppression of lymphocyte function

Natural suppressor (NS) cells, which nonspecifically suppress immune responses, are present in the spleen following exposure to radiation, chronic graft-versus-host disease, or cancer and in normal bone marrow. A model system is described which allows the study of cytokines activating and inhibiting NS cells, cytokines mediating NS activity, and NS effects on cytokine synthesis. Recombinant interleukin-3 (rIL-3) and granulocyte-macrophage colony-stimulating factor (rGM-CSF) efficiently activated NS cells present in normal bone marrow and were effective at concentrations as low as 5 U/ml. At high concentrations, GM-CSF, but not IL-3, did not activate NS cells. Recombinant interferon-gamma (rIFN-gamma) blocked the activation of bone marrow NS cells by rIL-3, but did not down-regulate NS cells once activated. The NS cells secreted one or more soluble suppressor factors, which blocked IL-2 synthesis and also inhibited IL-2-dependent T cell proliferation in the presence of excess IL-2.