Biomedical subjects

C J Burger

Publications and source records attributed to C J Burger.

At least 19 recordsLinked to original sources

PubMed1994

Tumor-induced regulation of suppressor macrophage nitric oxide and TNF-alpha production. Role of tumor-derived IL-10, TGF-beta, and prostaglandin E2.

In vitro-activated macrophages (Mphi) co-express cytotoxicity for tumor cells and suppression of lymphocyte proliferation. These Mphi functions increase during tumor growth and are mediated by soluble molecules. Because Mphi-derived nitric oxide (NO) and TNF-alpha mediate both cytotoxicity and suppression, we determined whether fibrosarcoma (Meth-KDE) growth increased Mphi-mediated suppression of T cell proliferation by increasing Mphi NO and TNF-alpha production. Tumor-bearing host peritoneal Mphi produced more NO and TNF-alpha than normal host Mphi when activated with IFN-gamma or LPS, respectively. This tumor-induced increase in Mphi NO and TNF-alpha production mediated suppression of alloantigen-driven T cell proliferation, because treatment with either NG-monomethyl-L-arginine or anti-TNF-alpha Ab blocked tumor-bearing host Mphi-mediated suppression. TNF-alpha did not directly suppress T cells, but it induced Mphi NO production that down-regulated proliferation. When non-tumor-infiltrating peritoneal Mphi were cultured with Meth-KDE cell supernatants, Mphi production of NO and TNF-alpha was strongly down-regulated. The tumor-derived molecules responsible for this inhibition were IL-10, TGF-beta 1, and prostaglandin E2. The experimental evidence leading to this conclusion included: 1) The Meth-KDE cells produced significant levels of these cytokines. 2) Recombinant forms of these cytokines suppressed NO and TNF-alpha production. 3) Ab-mediated absorption of these cytokines from tumor cell supernatants restored NO and TNF-alpha production. 4) Anti-IL-10 and anti-TGF-beta 1 Ab addition to IFN-gamma-stimulated Mphi restored NO production. Culture supernatants of two human carcinoma cell lines and another murine fibrosarcoma suppressed Mphi NO and TNF-alpha production, which was partly mediated by TGF-beta 1 and prostaglandin E2. Collectively, these results suggest that tumor growth promotes distal Mphi suppressor activity by increasing Mphi production of cytotoxic molecules and concomitantly down-regulating the local production of these antitumor molecules.

Animals↗

PubMed1994

Tumor growth alters T cell and macrophage production of and responsiveness to granulocyte-macrophage colony-stimulating factor: partial dysregulation through interleukin-10.

Tumor growth induces phenotypic and functional changes among splenic T cells and macrophages (M phi) that contribute to the immunosuppression observed in tumor-bearing hosts (TBH). These changes partly arise through alterations in immune cell production of and responsiveness to cytokines. Granulocyte-macrophage colony-stimulating factor (GM-CSF) is an important T cell- and M phi-derived cytokine that is produced during normal host immunogenic challenge, but it's involvement during cancer is poorly defined. In contrast, interleukin-10 (IL-10) is an inhibitory cytokine that is produced by immune cells as a deactivation factor. IL-10 can disrupt GM-CSF synthesis and may be associated with tumor-induced changes in cytokine synthesis. We determined if tumor growth alters T-cell and M phi synthesis of and responsiveness to GM-CSF, and if these alterations occur because tumor growth heightens immune cell sensitivity to IL-10. Tumor growth significantly decreased T-cell synthesis of GM-CSF during activation by concanavalin A, and TBH T cells were more susceptible to GM-CSF synthesis inhibition by IL-10 than their normal host (NH) counterparts. This suppression was observed using both unseparated splenic lymphocyte preparations and purified CD4+ and CD8+ T cells. Similarly, TBH M phi (both splenic and peritoneal) produced less GM-CSF than NH M phi during activation by lipopolysaccharide. Tumor growth also altered major histocompatibility complex (MHC) class II- M phi GM-CSF synthesis. TBH M phi were more susceptible to GM-CSF synthesis inhibition by IL-10 than their NH counterparts. Although TBH T cells demonstrate less proliferation than NH T cells during activation, tumor growth did not compromise T-cell responsiveness to GM-CSF. However, tumor growth did increase TBH T-cell susceptibility to inhibition of proliferation by IL-10. Tumor growth suppressed M phi responsiveness to GM-CSF, and IL-10 further decreased M phi responsiveness to GM-CSF. Collectively, these results suggest that T cell and M phi production of and responsiveness to GM-CSF is disrupted during tumor growth, and that TBH T cells and M phi are more susceptible to the suppressor activity of IL-10 than their NH counterparts.

Animals↗

PubMed1994

Tumour growth causes suppression of autoreactive T-cell proliferation by disrupting macrophage responsiveness to interferon-gamma.

Normal immune homeostasis is regulated partly by a small population of CD4+ T cells that react to autologous major histocompatibility complex class-II molecules on self-cells. Decreased autoreactive T-cell responses are associated with cancer. Tumour growth causes syngeneic macrophages (M phi) to suppress autoreactive T-cell proliferation by decreasing M phi class-II expression and increasing M phi production of the suppressor molecule prostaglandin E2 (PGE2). Because interferon-gamma (IFN-gamma) is a potent M phi activation molecule which regulates both M phi PGE2 and class-II expression, the effects of IFN-gamma on tumour-induced suppression of autoreactive T-cell proliferation were investigated. Exogenous IFN-gamma increased normal host (NH) CD4+ autoreactive T-cell proliferation stimulated by syngeneic NH M phi but decreased proliferation stimulated by tumour-bearing host (TBH) M phi. Antibody (Ab) neutralization of endogenous IFN-gamma activity reduced TBH M phi-mediated suppression. Kinetic studies showed that endogenous IFN-gamma suppressor activity was not exclusive during T-cell activation. Indomethacin treatment blocked IFN-gamma-induced suppression in TBH M phi-T cell cultures. TBH M phi-T cell cultures contained significantly more PGE2 than those containing NH M phi. Exogenous IFN-gamma increased early PGE2 production in TBH M phi cultures but decreased production in NH M phi cultures. The Ab-mediated neutralization of endogenous transforming growth factor-beta or tumour necrosis factor-alpha reduced TBH M phi-mediated suppression and blocked IFN-gamma-induced suppression. Short-term treatment of M phi with IFN-gamma before their addition to T cells caused TBH M phi to stimulate T-cell proliferation, which suggests that early suppressor molecule production by TBH M phi inhibits synthesis or activity of IFN-gamma-induced stimulatory monokines. These results show that tumour growth causes M phi to suppress autoreactive T-cell responses by allowing IFN-gamma to induce M phi suppressor molecules, which block production or activity of stimulatory monokines.

Animals↗

PubMed1994

Macrophage priming and activation during fibrosarcoma growth: expression of c-myb, c-myc, c-fos, and c-fms.

Macrophages (M phi)3 function by a two-step process that includes priming (induction of cytokine and enzyme mRNA) and activation (production of effector molecules). The initial steps in M phi priming involve the expression of certain proto-oncogenes that regulate expression of other genes. Because tumor growth primes M phi to produce several suppressor monokines, we determined if cancer induced M phi expression of these proto-oncogenes. Unstimulated peritoneal M phi from tumor-bearing hosts (TBH) constitutively expressed the proto-oncogenes c-fms, c-fos, c-myc, and c-myb, whereas normal host (NH) M phi had little or no expression of these proto-oncogenes. When M phi were given a 24-h adherence priming stimulus, NH M phi expressed c-fms and c-fos at levels equivalent to TBH M phi constitutive expression. Adherence had little or no effect on c-fms and c-fos expression in TBH M phi or on NH and TBH M phi c-myc expression. c-myb expression was not induced in NH M phi during adherence and was strongly decreased in TBH M phi. Activation with a 1-h lipopolysaccharide-treatment increased NH and TBH M phi expression of c-fms, c-fos, and c-myc, with higher expression of these proto-oncogenes in TBH M phi. Activation failed to induce c-myb expression in NH M phi and completely inhibited expression in TBH M phi. Because c-fms, c-fos, and c-myc are normally expressed early during M phi activation, our results suggest that tumor growth primes M phi by inducing expression of these proto-oncogenes. c-myb is expressed in immature M phi and is downregulated during M phi activation. These observations explain why NH M phi expression of c-myb was not induced and are consistent with reports that suggest TBH M phi have not reached full developmental maturity. The induction of M phi proto-oncogene expression during cancer may put M phi in a primed state, which leads to earlier and stronger production of adverse suppressor and cytotoxic molecules.

Animals↗

PubMed1994

Increased sensitivity of tumor-bearing host macrophages to interleukin-10: a counter-balancing action to macrophage-mediated suppression.

Tumor growth causes macrophages (M phi) to suppress T-cell proliferation by inducing M phi production of soluble suppressor molecules. Because interleukin (IL)-10 inhibits production of most M phi-derived molecules, we investigated the effects of IL-10 on murine M phi suppressor function during tumor growth. When acting as accessory cells during alloantigen-induced CD4+ T-cell proliferation, syngeneic tumor-bearing host (TBH) peritoneal M phi suppressed normal host (NH) T-cell proliferation more than their normal counterparts. Exogenous IL-10 suppressed alloantigen-stimulated CD4+ T-cell proliferation in the absence of accessory M phi, but it blocked TBH M phi-mediated suppression. IL-10 pretreatment of M phi reversed suppression mediated by TBH M phi but did not affect NH M phi activity. Supernatant transfer experiments showed that IL-10 blocked TBH M phi-mediated suppression by inhibiting soluble suppressor molecule production. Activated TBH M phi produced greater quantities of the suppressor molecules tumor necrosis factor-alpha, nitric oxide, prostaglandin E2, and granulocyte-macrophage colony-stimulating factor than NH M phi did. Exogenous IL-10 reduced production of these molecules by TBH M phi more than by NH M phi. Activated TBH M phi produced more IL-10 than NH M phi, suggesting that endogenous IL-10 contributes to increased TBH M phi sensitivity to exogenous IL-10's inhibitory action. The antibody-mediated neutralization of endogenous IL-10 activity relieved NH, but not TBH, M phi-mediated suppression of T-cell proliferation. This result supports the idea that TBH M phi are more sensitive to the inhibitory action of IL-10 on suppressor molecule production. IL-10 is known to inhibit M phi antigen-presenting cell-dependent helper T-cell proliferation. We report here that IL-10 restores TBH helper T-cell functions by blocking accessory M phi production of inhibitory molecules. This restoration suggests that IL-10's M phi deactivating activity provides an upregulatory role in immunocompromised individuals where suppressor M phi are abundant.

Animals↗

PubMed1993

Tumor growth and adherence change the expression of macrophage Mac-2.

The galactose-specific animal lectin, Mac-2, has been identified in macrophage (M phi) membrane, cytoplasmic, and nuclear fractions. Flow cytometric analyses showed that there is a decrease in membrane Mac-2 during tumor growth. After 24-h adherence there was an increase in the number of normal host (NH) and tumor-bearing host (TBH) Mac-2+ M phi. Immunoblot analyses of NH and TBH M phi identified changes in the subcellular localization of Mac-2. The increase in nuclear Mac-2 during tumor growth, and after prolonged adherence of NH and TBH M phi, correlates with an increase in M phi entering the late G1 phases of the cell cycle. Northern blot analyses showed an increase in Mac-2 mRNA during tumor growth, and an increase in NH and TBH M phi after 24-h adherence. Tumor growth is able to manipulate the immune system through M phi by causing a down-regulation in membrane Mac-2 and an up-regulation in intracellular Mac-2. NH and TBH M phi respond to adherence by expressing increased membrane and nuclear Mac-2, but TBH M phi response is lower.

Animals↗

PubMed1993

Tumor growth increases Ia- macrophage synthesis of tumor necrosis factor-alpha and prostaglandin E2: changes in macrophage suppressor activity.

Although tumor growth enhances macrophage (m phi) cytotoxic activity by increasing their tumor necrosis factor-alpha (TNF-alpha) production, increased prostaglandin E2 (PGE2) synthesis reduces most immune responses during tumor growth. Macrophages that do not express major histocompatibility complex class II molecules (Ia- m phi) are the predominant suppressor and cytotoxic population and are more abundant in tumor-bearing hosts (TBHs). This study determined if TBH Ia- m phi s are the major population producing TNF-alpha and PGE2 and if these molecules affect Ia- m phi-mediated suppression of alloantigen-stimulated T cell proliferation. Normal host (NH) and TBH splenic Ia(+)-depleted (Ia-) m phi s synthesized more TNF-alpha than their respective whole populations (WPs) when cultured with lipopolysaccharide and interferon-gamma. TBH Ia- m phi s produced the most TNF-alpha. Northern blot analyses showed that Ia- m phi s had higher amounts of TNF-alpha mRNA expression than their respective WP, and TBH Ia- m phi s expressed the highest amounts of TNF-alpha mRNA. When WP and Ia- NH and TBH m phi s were added to alloantigen-stimulated T cells, suppression of T cell proliferation mediated by Ia- m phi s was greater than by their respective WP. TBH Ia- m phi s were most suppressive. The blockage of PGE2 production reduced suppression mediated by TBH Ia- m phi s more than by all other m phi populations. A PGE2-specific enzyme-linked immunosorbent assay showed that PGE2 production was greater in Ia- m phi- than in WP m phi-containing cultures and greatest in cultures containing TBH Ia- m phi s. Because TNF-alpha enhances T cell responses, its effects on Ia- m phi PGE2-mediated suppression was determined. When TNF-alpha was added to m phi-containing T cell cultures, TNF-alpha directly stimulated NH, but not TBH, Ia- m phi s, which enhanced T cell proliferation. However, inhibiting PGE2 production allowed TNF-alpha to stimulate T cell proliferation in TBH Ia- m phi-containing cultures. Collectively, these data show that Ia- m phi s are the major TNF-alpha- and PGE2-producing cells and that these molecules are partly responsible for the tumor-induced increase in m phi-mediated cytotoxicity and suppression, respectively. TNF-alpha not only mediates cytotoxicity but also counteracts Ia- m phi PGE2-mediated suppression. Although tumor growth increases Ia- m phi TNF-alpha production, enhanced PGE2 production blocks TNF-alpha's stimulatory action on Ia- m phi s, which favors their suppressor function during tumor growth.

Animals↗

PubMed1993

Fibrosarcoma-induced increase in macrophage tumor necrosis factor alpha synthesis suppresses T cell responses.

Tumors down-regulate T cell responses partly by increasing macrophage (m phi) production of the suppressive molecule prostaglandin E2 (PGE2). Because tumor growth increases m phi tumor necrosis factor alpha (TNF-alpha) production and TNF-alpha stimulates m phi PGE2 synthesis, we examined the contribution of TNF-alpha to fibrosarcoma-induced m phi-mediated suppression of alloreactive CD4+ T cell proliferation. We showed that tumor-bearing host (TBH) m phi s express high levels of TNF-alpha mRNA, which leads to increased lipopolysaccharide-induced TNF-alpha production. Tumor cells were directly involved in m phi TNF-alpha synthesis because fibrosarcoma cells induced normal host (NH) m phi s to produce TNF-alpha. Addition of TBH m phi s to allogeneic mixed lymphocyte reaction (MLR) cultures suppressed CD4+ T cell proliferation more than NH m phi s. The neutralization of endogenous TNF-alpha activity with anti-TNF-alpha antibody (Ab) treatment reversed TBH, but not NH, m phi-mediated suppression. Conversely, exogenous TNF-alpha increased NH or TBH m phi-mediated suppression but stimulated T cell proliferation without m phi s. Kinetic treatment of MLR cultures with anti-TNF-alpha Ab or TNF-alpha showed that TNF-alpha production and activity occurred at the beginning of T cell proliferation. When arachidonic acid metabolite synthesis was inhibited, TNF-alpha-induced suppression was blocked in NH m phi-containing cultures and completely reversed in TBH m phi-containing cultures. A PGE2-specific enzyme-linked immunosorbent assay showed that TNF-alpha addition increased PGE2 production in NH m phi-containing cultures to that of TBH m phi-containing cultures. Exogenous PGE2 did not affect the TNF-alpha enhancement of T cell proliferation without m phi s. Therefore, suppression induced by TNF-alpha was caused by increased m phi PGE2 production and not by TNF-alpha in concert with PGE2. Even though TNF-alpha is known to enhance lymphocyte proliferation, we show that in the presence of m phi s, the main TNF-alpha producers, TNF-alpha suppresses T cell proliferation. Perhaps increased TNF-alpha production during pathological states, such as cancer, triggers the initial stages of suppression.

Animals↗

PubMed1993

Tumor-induced modulation of macrophage class II MHC molecule mRNA expression.

Class II MHC protein expression in macrophages (M phi) is reduced during tumor growth. Because regulation of class II MHC proteins occurs during transcription, tumor growth may suppress class II MHC protein expression by suppressing mRNA. The decrease in class II mRNA may result from (i) a decrease in M phi responsiveness to an inducing agent, such as interferon-gamma (IFN-gamma), or (ii) an increase in M phi sensitivity to suppressing agents, such as prostaglandin E2 (PGE2). To determine how tumors induce suppression of class II mRNA, M phi were cultured in the presence of IFN-gamma with or without other factors, and Northern blot analyses were performed. Unstimulated normal host (NH) or tumor-bearing host (TBH) M phi do not express detectable class II mRNA. The addition of IFN-gamma induces class II mRNA expression in NH and TBH M phi, but class II mRNA expression is significantly lower in TBH M phi. Kinetic studies suggested that NH M phi class II mRNA is induced faster and in greater amounts than TBH M phi class II mRNA. There is a decrease in M phi class II mRNA stability during tumor growth that may account for the decreased induction by IFN-gamma. Lipopolysaccharide (LPS) suppresses class II mRNA induction in both NH and TBH IFN-gamma-treated M phi, but TBH M phi are more sensitive to its suppression. PGE2 and tumor-necrosis factor-alpha (TNF-alpha), two factors produced by LPS-stimulated M phi, were tested for their ability to modulate class II mRNA expression in NH and TBH IFN-gamma-treated M phi. PGE2 suppressed class II mRNA expression in both NH and TBH M phi. The addition of TNF-alpha to IFN-gamma-treated M phi suppressed class II mRNA in NH M phi but, surprisingly, had an additive effect on IFN-gamma-induced class II mRNA expression. TNF-alpha did not induce class II mRNA expression in TBH M phi in the absence of IFN-gamma. The cause of the reduced class II mRNA expression during tumor growth is a decreased response to IFN-gamma and an increased sensitivity to PGE2. This change may cause the observed suppression mediated by TBH M phi.

Animals↗

PubMed1993

Tumor-induced macrophage tumor necrosis factor-alpha production suppresses autoreactive T cell proliferation.

T cells can react to self-cells bearing the syngenic major histocompatibility complex class II molecule Ia. Decreased autoreactive T cell responses are associated with cancer. Tumor growth causes syngeneic macrophages (M phi) to suppress autoreactive T cell proliferation by decreasing M phi Ia expression and increasing M phi production of the suppressor molecule prostaglandin E2 (PGE2). Because M phi produce tumor necrosis factor-alpha (TNF-alpha) during cancer, and TNF-alpha stimulates M phi PGE2 synthesis, we determined if TNF-alpha mediates tumor-induced suppression of autoreactive T cell proliferation stimulated by syngeneic M phi. We showed that tumor growth increases TNF-alpha production because tumor-bearing host (TBH) M phi synthesized more TNF-alpha than normal host (NH) M phi when cultured with lipopolysaccharide. Exogenous TNF-alpha increased NH CD4+ autoreactive T cell proliferation stimulated by syngeneic NH M phi but not by TBH M phi. When endogenous TNF-alpha activity was neutralized by anti-TNF-alpha antibody addition, T cell proliferation decreased when stimulated by NH M phi but increased when stimulated by TBH M phi. Kinetic studies showed that TNF-alpha affected M phi-stimulated T cell proliferation during the first few hours (4h) of the 96 h culture time. Indomethacin-treatment allowed TNF-alpha to increase T cell proliferation stimulated by TBH M phi. A PGE2-specific enzyme-linked immunosorbent assay showed that TBH M phi T cell cultures contained significantly more PGE2 than those containing NH M phi, and that exogenous TNF-alpha increased PGE2 production in TBH M phi cultures more than in NH M phi cultures. Short-term (4h) pretreatment of M phi with TNF-alpha increased T cell proliferation stimulated by NH, but not TBH, M phi. However, long-term (16 h) TNF-alpha pretreatment reversed TBH M phi-mediated suppression, suggesting that early suppressor molecular production inhibits synthesis or activity of TNF-alpha-induced stimulatory monokines. Although TNF-alpha is known to increase T cell proliferation, these results show that the tumor-induced increase in M phi TNF-alpha synthesis suppress autoreactive T cell proliferation, which is mediated by PGE2 production.

Animals↗

PubMed1993

Ia- macrophages and cytokine networks contribute to tumor-induced suppression of CD4+ autoreactive T cells.

Tumor growth changes the functions and phenotypes of macrophages (M phi) and T cells. Suppression of CD4+ T cell autoresponses during tumor growth was contributed primarily by M phi. Tumor-induced alterations in the abilities of these cells to mediate autorecognition were assessed through syngeneic mixed lymphocyte reaction (SMLR) assays. Tumor-bearing host (TBH) M phi were significantly more suppressive (60-90%) than normal host (NH) M phi, and this suppression was caused partly by reduced Ia expression. TBH Ia- M phi were significantly more suppressive (50-80%) than their NH counterparts. The suppression mechanism was controlled partly by prostaglandin E2 (PGE2), because treating cultures with indomethacin and titrated NH and TBH Ia- M phi led to increased T-cell responsiveness, although responsiveness never reached levels of assays containing unseparated M phi. Blocking studies using anti-interferon-gamma (anti-IFN-gamma) monoclonal antibodies (mAb), anti-interleukin 4 (anti-IL-4) mAb, and indomethacin suggested that IFN-gamma, IL-4, and PGE2 contributed to tumor-induced M phi-mediated suppression. Our results suggested that a quantitative shift in M phi phenotype and a qualitative shift in M phi function in addition to differences in cytokine-directed accessory activities are partly responsible for tumor-induced suppression CD4+ T cell autoresponses.

Animals↗

PubMed1992

Macrophages stimulated by receptor-ligand interactions exhibit differences in cell-cycle kinetics during tumor growth: stimulation at Mac-1 and Mac-3 receptors alters DNA synthesis.

Phenotypic and functional changes associated with tumor-bearing host (TBH) macrophages (M phi) are partly responsible for immunosuppression during tumor growth. Flow cytofluorometric analyses revealed differences in cell-cycle kinetics between normal host (NH) and TBH M phi that were stimulated at specific receptors. Receptor-ligand interactions were induced by antibodies against Mac-1, -2, -3, and Ia receptors and changes in DNA synthesis were measured over a 12-h time course by incorporation of propidium iodide. TBH M phi showed higher DNA synthesis than NH M phi over this time course irrespective of the receptor induced. NH M phi stimulated at the Mac-1 receptor demonstrated higher DNA synthesis than control NH M phi although TBH M phi stimulated at this receptor and control TBH M phi failed to show any differences. Both NH and TBH M phi exhibited small, short-term decreases in DNA synthesis when stimulated at the Mac-2 receptor. TBH M phi that were stimulated at the Mac-3 receptor demonstrated higher DNA synthesis than their control counterparts while NH M phi stimulated at this receptor and control NH M phi showed identical levels of DNA synthesis. No differences in DNA synthesis were found among normal or TBH M phi that were stimulated through Ia. Differences in DNA synthesis did not appear to be attributable to differences in receptor expression. Further analysis of Mac-1 and Mac-3 stimulated cells revealed that DNA synthesis in NH M phi stimulated at the Mac-1 receptor returned to control levels at 48 h.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1992

Cytokines and suppressor macrophages cause tumor-bearing host CD8+ T cells to suppress recognition of allogeneic and syngeneic MHC class II molecules.

Quantitative and qualitative tumor-associated changes in T cell phenotype and function were identified in CD8+ T cells. Tumor growth changed splenic CD4+/CD8+ T cell ratios and induced the appearance of more cells with the CD8+ phenotype. In comparison to equal concentrations of normal host (NH) counterparts, tumor-bearing host (TBH) CD8+ T cells were highly suppressive to allorecognition and autorecognition. Suppression was not due to quantitative reductions in CD4+ T cells, although minor qualitative differences were observed. Suppression appeared to be mediated partly by prostaglandin E2 (PGE2). Interferon-gamma (IFN-gamma) and interleukin-4 (IL-4) contributed to TBH CD8+ T cell-mediated suppression. Blocking studies using monoclonal antibodies (mAb) in conjunction with indomethacin suggested that cytokine networks involving IFN-gamma, IL-4, and PGE2 were disrupted during tumor growth and promoted TBH CD8+ T cell suppression. Alloresponses and autoresponses were significantly suppressed when TBH CD8+ T cells mediated these reactions simultaneously with TBH Ia- macrophages. Inhibition of PGE2 production was unable to reverse the additive suppression caused by these two cell types. These results collectively suggest that tumor-induced changes in CD8+ T cells lead to suppressed allo-recognition and autorecognition through both soluble mediator molecules and cellular interactions.

Animals↗

PubMed1992

Tumor growth changes the contribution of granulocyte-macrophage colony-stimulating factor during macrophage-mediated suppression of allorecognition.

Tumor-bearing host (TBH) macrophages (M phi) suppress T cell alloresponses, and this study suggests granulocyte-macrophage colony-stimulating factor (GM-CSF), a molecule associated with suppressive M phi activity during tumor growth, signals more immunosuppression. In the absence of M phi, GM-CSF increased T cell proliferation in response to alloantigen. However, TBH M phi-mediated suppression of allorecogntion was further induced by GM-CSF. Allogeneic mixed lymphocyte reaction (MLR) cultures, containing normal host (NH) M phi, were either unaffected or enhanced. Prostaglandin E2 (PGE2), a highly suppressive monokine that decreases alloreactivity, did not seem to be involved in the suppression caused by the TBH M phi/GM-CSF interaction. M phi-CSF (M-CSF) addition to cultures did not reverse the suppression caused by TBH M phi and GM-CSF, and inhibition of PGE2 synthesis did not change the response to M-CSF. TBH Ia- M phi, a suppressor population that predominates among splenic M phi during tumor growth, demonstrated significantly lower reactivity in the presence of GM-CSF. In contrast, alloresponses suppressed by NH Ia- M phi demonstrated higher reactivity in the presence of GM-CSF. The data collectively suggest that TBH M phi respond differently to GM-CSF, and that tumor-induced changes in GM-CSF responsiveness affect M phi accessory ability.

Animals↗

PubMed1992

Tumor growth changes responsiveness to and production of granulocyte-macrophage colony-stimulating factor during recognition of self MHC class II molecules.

Tumor growth decreases T-cell recognition of self major histocompatibility complex (MHC) class II molecules by inducing changes in splenic macrophage (M phi) phenotype and function. The current investigation shows tumor-induced alterations in autorecognition also are associated with changes in responsiveness to and production of granulocyte-M phi colony-stimulating factor (GM-CSF). In contrast to normal host (NH) M phi, tumor-bearing host (TBH) M phi failed to express higher MHC class II molecule density after exposure to GM-CSF. Autoreactive T cells stimulated by either NH or TBH M phi were suppressed by GM-CSF. Inhibition of prostaglandin E2 (PGE2) synthesis reversed M-CSF-induced suppression of autoreactivity to NH M phi and, to a lesser extent, to TBH M phi. When TBH autoreactive T cells were stimulated by TBH M phi, autoreactivity increased when GM-CSF was added and PGE2 synthesis was inhibited. Although GM-CSF can contribute to tumor-induced suppression, it did not affect the contribution of GM-CSF during autorecognition. Increased GM-CSF production was responsible, at least in part, for the TBH M phi-mediated suppression. Low concentrations of GM-CSF were produced endogenously by tumor isolates, and GM-CSF production was significantly increased when isolates were stimulated with lipopolysaccharide. Autoreactive T cells stimulated solely by TBH M phi produced more GM-CSF than autoreactive T cells stimulated by NH M phi. Cultures supplemented with several concentrations of NH or TBH M phi produced similar amounts of GM-CSF in a dose-dependent manner. Inhibition of PGE2 synthesis by NH and TBH M phi reduced GM-CSF production equally. Collectively, these results suggest that during tumor growth, responsiveness to and production of GM-CSF alters recognition of self MHC class II molecules.

Animals↗

PubMed1990

Tumor modulation of autoreactivity: decreased macrophage and autoreactive T cell interactions.

The autologous mixed lymphocyte reaction (AMLR) is an in vitro measure of autoreactivity, a key mechanism in immune homeostasis. In this system, macrophages (M phi) act as accessory cells to autoreactive L3T4+ T cells by presenting self-Ia and releasing soluble modulators. During tumor growth, changes occur in M phi and T cells. Tumor-bearing host (TBH) M phi have a reduced ability to act as accessory cells. In fact, TBH M phi suppressed autoreactivity by 60-70%. The decrease in TBH M phi or T-cell abilities was not due to differences in cell numbers or incubation time. Because tumor growth causes increased prostaglandin E2 (PGE2) production by M phi, indomethacin was used to assess the contribution of prostaglandins. Normal and TBH T-cell reactivity increased nearly 50% when stimulated by normal host M phi, while normal and TBH T-cell reactivity increased nearly 100% when stimulated by TBH M phi. Thus increased prostaglandin production is partly responsible for the increased TBH suppressor M phi activity and in the normal host, suppressor M phi may be responsible for maintaining immune regulation. To assess the direct role of prostaglandins in T-cell hyporesponsiveness, PGE2 was titrated into the cultures. PGE2 suppressed normal and TBH T-cell responsiveness in a dose-dependent manner. Normal host T cells were suppressed to a greater extent than TBH T cells by PGE2 (66% versus 42% suppression, respectively). Reduced Ia expression and active suppressor mechanisms are not the only mechanisms mediating hypoautoreactivity during tumor growth. TBH autoreactive L3T4+ T cells were less responsive to self-Ia; they were only 60-80% as reactive as their normal counterparts. To address whether the helper T (TH)-cell defect involved cytokines, T cells were treated with interleukin (IL)-1, IL-2, and IL-4. In all cases, the TBH T-cell response to the factors was decreased (only 60-75% as reactive as normal T cells). Because TBH M phi-mediated suppression can override the addition of IL-1, IL-2, and IL-4, indomethacin was also added with the exogenous interleukins. This coaddition significantly enhanced normal host autoreactivity above control levels while TBH autoreactivity (the combination of TBH T cells and TBH M phi) only returned to normal host unstimulated levels. Tumor growth modulates the immune response at least by (i) decreasing the accessory cell abilities of TBH M phi through decreased Ia expression and increased production of suppressive molecules such as prostaglandins; and (ii) decreasing the responsiveness to immune enhancing factors by TH cells.

Animals↗

PubMed1990

Two-color flow cytometric analysis of the expression of MAC and MHC class II antigens on macrophages during tumor growth.

Tumor-bearing host (TBH) macrophages (M phi) exhibit immune dysfunction that is concomitant with phenotypic changes. We examined M phi subpopulations by changes in the expression of surface antigens Mac-1, -2, -3, and Ia on normal and TBH peritoneal and splenic M phi. M phi were double-labeled and analyzed by flow cytometry to observe multiple expression of surface antigens. Tumor growth alters the multiple expression of these M phi markers. Peritoneal and splenic M phi had different Mac+ and Mac+Ia+ population percentages. In TBH, peritoneal M phi had decreased percentages of Mac-1+2+, Mac-1+3+, Mac-2+3+, and Mac+Ia+ M phi. This decrease correlated with functional changes in TBH M phi. In contrast, there was an increase in Mac-2-Ia- TBH peritoneal M phi. Previously undiscovered Mac-1+2-3- and Mac-1-2-3+ populations were found. In contrast to peritoneal M phi, there was an increase in the percentage of Mac-1+2+, Mac-1+3+, and Mac-2+3+ splenic TBH M phi but, like peritoneal M phi, there was a decrease in the percentage of Mac+Ia+ M phi. Also, TBH splenic M phi showed a smaller but more uniform antigen density than normal host splenic M phi. Tumor growth modulated phenotypic alterations in peritoneal and splenic M phi subpopulations. Combined with earlier functional studies of M phi subpopulations, these data suggested a relationship between changes in M phi phenotype and tumor-induced dysfunction of M phi-modulated immune activity.

Animals↗

PubMed1990

Modulation of alloreactivity by Mac-1+, -2+, and -3+ macrophages from normal and tumor-bearing hosts: flow cytofluorometrically separated macrophages.

Macrophages (M phi) are multifunctional cells that regulate humoral and cellular immune responses. Our studies of tumor-induced M phi-mediated dysfunction used M phi subsets which were defined by their Mac-1, Mac-2, and Mac-3 surface markers. To measure the accessory activity of M phi for T cell alloreactivity, thioglycollate-elicited peritoneal M phi from normal and tumor-bearing hosts (TBH) were labeled with anti-Mac-1, -2, or -3 antibodies and separated by flow cytofluorometry. The separated Mac-1+, -2+, and -3+ M phi were called sorted M phi, while unseparated M phi were designated unsorted M phi. Both M phi types were added to mixed lymphocyte reaction (MLR) cultures at concentrations ranging from a low of 2% M phi to a high of 20% M phi. The low concentration of unsorted normal host M phi caused a 31% suppression of alloreactivity. Suppression reached 68% when high concentrations of unsorted normal host M phi were added to the MLR cultures. Unsorted TBH M phi reduced alloreactivity by 64% and 86% at low and high concentrations, respectively. When separated into subpopulations, normal host Mac-1+ M phi reduced alloreactivity by 48% and 81% when added at low and high concentrations, respectively. TBH Mac-1+ reduced alloreactivity by 31% and 59% at low and high concentrations, respectively. There were no differences in the suppression caused by normal or TBH Mac-2+ M phi, and by normal or TBH Mac-3+ M phi. Indomethacin treatment did not effect the suppression caused by Mac-1+ M phi, suggesting that proataglandin E2 was not involved. Indomethacin treatment did reduce suppression mediated by Mac-2+, -3+, and unsorted M phi. Mac-2+ M phi dramatically enhanced alloreactivity at low concentrations with normal host Mac-2+ M phi providing greater enhancement of alloreactivity than TBH Mac-2+ M phi. The division of M phi into subpopulations on the basis of Mac antigens suggested that Mac-1+ and -3+ M phi played a major role in immunosuppression in the normal host, while Mac-3+ M phi were more active in TBH immunosuppression. Because no one population of sorted TBH M phi was more suppressive than sorted normal host M phi, we suggest that tumor-induced immunosuppression may involve a network of suppressor M phi.

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