Methotrexate specifically modulates cytokine production by T cells and macrophages in murine collagen-induced arthritis (CIA): a mechanism for methotrexate-mediated immunosuppression

Immunosuppressive therapy with methotrexate (MTX) has been established as effective treatment for patients with rheumatoid arthritis. To analyse the therapeutic potential and mechanisms of action of MTX, we determined serum cytokine levels and cytokine production by splenic T cells and macrophages in untreated and MTX-treated mice. Furthermore, we assessed the role of MTX in a murine model of experimental arthritis induced by collagen type II (CIA). MTX reduced spontaneous and IL-15-induced tumour necrosis factor (TNF) production by splenic T cells but not by macrophages from healthy mice in vitro in a dose-dependent manner. In contrast, interferon-gamma (IFN-γ) production was less strikingly reduced and IL-4 production was virtually unaffected. In addition, treatment of healthy mice with MTX in vivo led to reduced TNF serum levels and diminished TNF production by splenic T cells and macrophages. Intraperitoneal administration of MTX prior to the onset of arthritis completely prevented clinical and pathological signs of CIA. This was associated with a striking reduction of TNF production by spleen cells from MTX-treated mice. The role of TNF in MTX-mediated effects on cytokine production was further underlined by the finding that MTX effects on IFN-γ production were augmented in TNF-transgenic mice but abrogated in mice in which the TNF-α gene had been inactivated by homologous recombination. Thus, MTX specifically modulates spontaneous and IL-15-induced TNF-α production in mice and prevents experimental murine CIA. These data suggest that TNF production by T cells is an important target of MTX and may serve as a basis to understand and further analyse MTX-mediated mechanisms of immunosuppression in patients with RA.     

Enhanced macrophage responsiveness to lipopolysaccharide and CD40 stimulation in a murine model of inflammatory bowel disease: IL-10-deficient mice

OBJECTIVE: To elucidate the role of macrophages in the pathogenesis of inflammatory bowel disease, proinflammatory characteristics of macrophages were estimated in a murine model of spontaneous intestinal inflammation. MATERIALS AND METHODS: Peritoneal macrophages from IL-10deficient mice were stimulated with lipopolysaccharide (LPS) or an anti-CD40 monoclonal antibody (mAb). Cytokine release was assessed by enzyme-linked immunosorbent assay. CD40 expression was examined by two-color flow cytometric analysis. Induction of suppressor of cytokine signaling 3 (SOCS3) mRNA was evaluated by real-time quantitative RT-PCR. RESULTS: In the presence of LPS or anti-CD40 mAb, TNF-alpha and IL-12p70 release from macrophages of mutant mice was significantly higher than that from macrophages of wild-type mice. This may be due to the difference in IL-10 production by macrophages, since activated macrophages of wild-type mice produced IL-10 in amounts sufficient to suppress an increased release of cytokines from activated macrophages of mutant mice. LPS and CD40 stimulation induced significantly high level of SOCS3 expression in macrophages of mutant mice in comparison to those of wild-type mice. CONCLUSIONS: Macrophages from a murine model of inflammatory bowel disease demonstrated enhanced responsiveness to immunological and bacterial stimuli. This suggests significant roles of macrophages in the pathogenesis of inflammatory bowel disease.     

Increased IL-10 production during spontaneous apoptosis of monocytes

Monocytes/macrophages undergo apoptosis and are in contact with apoptotic cells both in vitro and in vivo. The data show that monocytes undergoing spontaneous apoptosis in vitro change their cytokine production profile. We demonstrate that the lipopolysaccharide (LPS)-induced production of interleukin-10 (IL-10) is up-regulated, while production of pro-inflammatory cytokines such as tumor necrosis factor-alpha (TNF-alpha) and interleukin-1beta (IL-1beta) is either not affected or reduced. These differences seen both at the protein and mRNA level directly correlate with the appearance of apoptotic cells in the culture. Flow cytometry analysis using double staining, surface with annexin V and intracellular with anti-IL-10, suggested that annexin V-negative monocytes are the predominant source of IL-10. Analysis of sorted populations of monocytes indicated that the increase in IL-10 synthesis appears to result from direct interactions between non-apoptotic and apoptotic cells at the time of stimulation. Also non-apoptotic, freshly isolated monocytes produced more IL-10 upon stimulation with LPS, Staphylococcus aureus or zymosan when apoptotic neutrophils were added to the culture. In contrast, monocyte-derived macrophages did not produce more IL-10 in the presence of apoptotic neutrophils. Finally, we found that the presence of apoptotic monocytes in the culture may influence specific immune responses. The data show that in the presence of annexin V-positive monocytes CD4-positive memory T cells produce less IFN-gamma upon stimulation with purified protein derivative of tuberculin, which could be partially reversed by anti-IL-10 neutralizing antibodies. We conclude that these findings might illustrate the mechanisms operating within an inflammatory site and play an important immunoregulatory role during the resolution of inflammation and specific immune responses.     

Thymulin, a thymic peptide, prevents the overproduction of pro-inflammatory cytokines and heat shock protein Hsp70 in inflammation-bearing mice

The effects of synthetic analogue of peptide hormone thymulin, which is normally produced by thymic epithelial cells, on immune cells activity and blood cytokine profile had been studied in male NMRI mice with acute inflammation induced by injection of lipopolysaccharide from gram-negative bacteria (LPS, 250 microg/100 g of body weight). Inflammation induced by LPS resulted in accumulation of several plasma pro-inflammatory cytokines, IL-1 beta, IL-2, IL-6, TNF-alpha, interferon-gamma, and also IL-10, anti-inflammatory cytokine. Thymulin previously injected in dose of 15 microg/100 g body weight, prevented the accumulation of proinflammatory cytokines in plasma. Thymulin also prevented LPS-induced up-regulation of production of several cytokines by spleen lymphocytes and peritoneal macrophages. Added in vitro, thymulin decreased the peak of TNF-alpha production in macrophages cultivated with LPS. In addition, thymulin lowered the peak of Hsp70 production induced by LPS treatment. The results indicate that thymulin having significant anti-inflammatory effect may be promising in clinical application.     

A novel synthetic lipid A analog with low endotoxicity, DT-5461, prevents lethal endotoxemia.

Bacterial endotoxin (lipopolysaccharide [LPS]) causes severe damage to the host organism as a result of excessive release of inflammatory cytokines, including interleukin-1 (IL-1) and tumor necrosis factor alpha (TNF-alpha), from mononuclear phagocytes during gram-negative bacterial infection. We evaluated the ability of a novel synthetic lipid A analog with low endotoxicity, DT-5461, to antagonize LPS-induced IL-1 and TNF-alpha production in cells of monocyte/macrophage lineage and examined the protective effect of DT-5461 against lethal endotoxic shock in mice. The IL-1- or TNF-alpha-inducing activity of DT-5461 is 100,000 to 10,000 times less active than that of Escherichia coli LPS (EcLPS) or synthetic lipid A. DT-5461 significantly inhibited EcLPS-induced IL-1 and TNF-alpha release when murine peritoneal macrophages were incubated with DT-5461 2 h prior to EcLPS stimulation at the same concentration (1 microgram/ml). The antagonistic effect of DT-5461 on the production of IL-1 and TNF-alpha induced by EcLPS occurred in a concentration-dependent manner. DT-5461 also inhibited IL-1 and TNF-alpha induction when murine peritoneal macrophages were stimulated by LPS from Salmonella typhimurium or synthetic lipid A, as well as by EcLPS, but not by muramyl dipeptides. This indicated that DT-5461 specifically antagonized the action of LPS. DT-5461 also antagonized EcLPS-mediated activation of human peripheral blood monocytes. DT-5461 blocked the binding of fluorescein isothiocyanate-labelled LPS to murine peritoneal macrophages as well as it did the binding of EcLPS and synthetic lipid A, i.e., in a concentration-dependent fashion. Injection of DT-5461 2 h before EcLPS challenge prevented the production of serum IL-1 and TNF-alpha in D-galactosamine-treated mice. Furthermore, this treatment modality protected mice against LPS-induced lethal toxicity. This study suggests that DT-5461 possesses a potent LPS antagonistic effect and may be useful in a protective strategy against lethal endotoxemia caused by gram-negative bacterial infection.     

Tumoristatic effects of anti-CD40 mAb-activated macrophages involve nitric oxide and tumour necrosis factor-alpha

Effector cells of the innate immune system have diverse functions that can result in tumour inhibition or tumour progression. Activation of macrophages by CD40 ligation has been shown to induce antitumour effects in vitro and in vivo. Here we investigated the role of nitric oxide (NO) and tumour necrosis factor-alpha (TNF-alpha) as mediators in the tumoristatic effects of murine peritoneal macrophages activated with agonistic anti-CD40 monoclonal antibody (alphaCD40) alone and following further stimulation with bacterial lipopolysaccharide (LPS). We found that macrophages activated in vivo by alphaCD40 exhibited tumoristatic activity in vitro against B16 melanoma cells; the tumoristatic effect correlated with the level of NO production and was enhanced by LPS. Use of the NO inhibitor L-nitro-arginine-methyl esterase (L-NAME) and evaluation of macrophages from inducible NO synthase (iNOS)-knockout (KO) mice following alphaCD40 activation showed reduced tumoristatic activity. CD40 ligation enhanced expression of TNF-alpha. Macrophage tumoristatic activity following alphaCD40 treatment was reduced by TNF-alpha mAb or use of macrophages from TNF-alpha-KO mice. However, further stimulation of alphaCD40-activated macrophages with LPS resulted in strong tumoristatic activity that was much less dependent on NO or TNF-alpha. Taken together, these results suggest that NO and TNF-alpha are involved in, but not solely responsible for, the antitumour effects of macrophages after activation by CD40 ligation.     

Colonic epithelial cell lines as a source of interleukin-8: stimulation by inflammatory cytokines and bacterial lipopolysaccharide.

Cytokines produced by intestinal epithelial cells may function as signals to neighbouring immune and inflammatory cells. We investigated production of the neutrophil and T-lymphocyte chemotactic cytokine interleukin-8 (IL-8) by intestinal epithelial cells using four colonic adenocarcinoma cell lines, T84, CaCo-2, HT29 and SW620, as a model system. These cell lines secreted substantial amounts of IL-8 if stimulated with IL-1 beta, tumour necrosis factor-alpha (TNF-alpha) or interferon-gamma (IFN-gamma), except CaCo-2 cells, which responded only to IL-1 beta. Bacterial lipopolysaccharide (LPS) was also an efficient stimulus of IL-8 release in SW620 and HT29 cells, whereas T84 and CaCo-2 cells were completely unresponsive to LPS, IL-8 secretion was greater at 4 hr after stimulation and was accompanied by induction of IL-8 messenger RNA. In T84 cells IFN-gamma and epidermal growth factor (EGF) stimulated IL-8 secretion synergistically with TNF-alpha, whereas in SW620 cells this synergism occurred only between IFN-gamma and TNF-alpha. IL-4, IL-10 and transforming growth factor-beta (TGF-beta), which can down-regulate IL-8 production in macrophages, had no effect on IL-8 generation by our cell lines. Adenocarcinoma cell culture supernatants also induced rapid transients of intracellular calcium in neutrophils. Depending on cell line and stimulus, supernatant bioactivity was completely or partially abrogated by neutralizing antibodies to IL-8, indicating that the cell lines investigated also generate other neutrophil-activating factors. IL-8 and possibly other chemokines generated by colonic adenocarcinomas may help to attract tumour-infiltrating leucocytes. Possibly, normal intestinal epithelial cells also have the potential to secrete this potent chemoattractant and thus might contribute to inflammatory responses of the intestinal mucosa, for example in inflammatory bowel disease.     

Benznidazole, a drug employed in the treatment of Chagas' disease, down-regulates the synthesis of nitrite and cytokines by murine stimulated macrophages.

Benznidazole (BZL) is a nitroheterocyclic drug employed in the chemotherapy of Chagas' disease, a protozoan disease caused by Trypanosoma cruzi. Because this parasite mostly replicates in macrophages, we investigated whether BZL was likely to modify the synthesis of macrophage mediators such as nitrite, tumour necrosis factor-alpha (TNF-alpha), IL-1beta, IL-6 and IL-10. Control and stimulated murine macrophages (lipopolysaccharide (LPS) and/or interferon-gamma (IFN-gamma)) were treated with BZL and measurements were carried out in culture supernatants collected 24 h later. Synthesis of nitrite, IL-6 and IL-10 was maximal upon combined stimulation with LPS + IFN-gamma, whereas lower amounts of the three mediators were detected when both stimuli were given alone. BZL treatment significantly reduced nitrite, IL-6 and IL-10 production, to undetectable levels in some cases, particularly IL-6 and IL-10. LPS was the most potent stimulus of IL-1beta and TNF-alpha production, followed by LPS + IFN-gamma and IFN-gamma in decreasing order. BZL partly inhibited TNF-alpha synthesis, but this effect was smaller than that observed for nitrite, IL-6 and IL-10. LPS-induced production of IL-1beta was also affected by BZL. Semiquantification of gene expression for inducible nitric oxide synthase (iNOS) showed that BZL completely inhibited iNOS gene induction by IFN-gamma, and resulted in respective inhibitions of 30% and 50% with LPS- and LPS + IFN-gamma-stimulated cells. BZL was not cytotoxic on macrophage cultures, as shown by the lactate dehydrogenase activity. Besides its trypanocidal activity, BZL may also alter the balance between pro- and anti-inflammatory mediators with important consequences for the course of T. cruzi infection.     

FcRγ deficiency improves survival in experimental sepsis by down-regulating TLR4 signaling pathway

Fc receptor common γ signaling chain (FcRγ), a common subunit shared by Fc receptors (FcγRI, III, IV, FcαRI, and FcεRI), is an important immune regulator both in innate and adaptive immunity. Previous studies have shown that FcRγ was a potential target of inflammatory diseases, whereas the role of FcRγ in sepsis has been poorly understood. In this study, we found that deficiency of FcRγ resulted in increased survival in lipopolysaccharide (LPS)/D-galactosamine and E. coli-induced sepsis in mice. This protective effect was characterized by decreased TNF-α, IL-6, and IL-10. Further experiments in bone marrow-derived macrophages (BMDMs) in vitro also showed that FcRγ deficiency resulted in decreased production of TNF-α, IL-6, and IL-10 upon LPS stimulation. The mechanism study showed that FcRγ was physiologically associated with toll-like receptor 4 (TLR4), and tyrosine phosphorylation of FcRγ mediated TLR4 signaling pathway, followed by increased ERK phosphorylation upon LPS stimulation. Our results suggest that FcRγ might be a potential therapeutic target of sepsis.

     

Pivotal advance: exposure to LPS suppresses CD4+ T cell cytokine production in Salmonella-infected mice and exacerbates murine typhoid

A number of studies have documented suppression of lymphocyte activation in mice infected with Salmonella. Here, we describe incomplete activation of CD4+ T cells following intravenous injection of specific peptide and LPS into Salmonella-infected mice. Although antigen-specific CD4+ T cells were activated by peptide/LPS to increase surface CD69 expression, they did not produce IL-2 or TNF-alpha. Suppression of cytokine production did not require prolonged exposure of the T cells to the Salmonella-infected environment, was not antigen specific, but was dependent upon the presence of LPS during stimulation. These data suggest that Salmonella-infected mice are exquisitely sensitive to the generation of a suppressive environment following innate immune stimulation with LPS. In agreement with this interpretation, repeated low-dose administration of LPS caused uncontrolled replication of attenuated Salmonella in vivo.     

Enhanced proinflammatory response to endotoxin after priming of macrophages with lead ions

Exposure to lead ions strongly enhances the susceptibility of rodents to endotoxin shock and parasitical infections. Macrophages play a key role during the immune response to lipopolysaccharide (LPS) and during the defense against parasites and might be a target of lead. In the present study, bone marrow-derived macrophages (BMMphi) pretreated with lead chloride prior to stimulation with LPS were analyzed for their release of immune mediators. Lead-pretreated cells released up to tenfold increased amounts of tumor necrosis factor-alpha (TNF-alpha), interleukin (IL)-6, IL-12, and prostaglandin E(2) (PGE(2)) but less IL-10 compared with controls. These effects were paralleled by enhanced mRNA levels and were dependent on the duration of lead pretreatment. Inhibition of protein kinase C or of protein synthesis during the priming phase blocked the lead-induced increase of TNF-alpha and IL-6 release. In conclusion, lead ions prime BMMphi for enhanced proinflammatory cytokine secretion in response to LPS, likely by activation of protein kinase C and subsequent synthesis of an unidentified mediator.     

Unraveling the lethal synergism between Trypanosoma cruzi infection and LPS: a role for increased macrophage reactivity

Various infections sensitize to lethal shock by promoting hyperactivation of macrophages to LPS stimulation. Although macrophages are thought to be deactivated upon contact with apoptotic cells during Trypanosoma cruzi infection, T. cruzi infection also sensitizes mice to endotoxemia. Herein, we studied the mechanisms of sensitization to endotoxemia in T. cruzi-infected mice in order to solve the paradox. Live (but not fixed) trypomastigotes from various stocks sensitized mice to endotoxemia. Mice deficient in glycolipid recognition (TLR2(-/-) and CD1d(-/-)) were sensitized by infection to challenge with LPS. Infected mice hyperproduced TNF and IL-10 upon LPS challenge. Infected TNF-R1(-/-), macrophage migration inhibitory factor (MIF)(-/-) and IFN-gamma(-/-) mice were lethally sensitized, but infected TNF-R1(-/-) mice administered anti-MIF survived shock with LPS. Macrophages from infected mice hyperproduced TNF in response to LPS stimulation and displayed increased expression of TLR4 compared to non-infected controls. Treatment with the PGE(2) synthesis inhibitor acetylsalicylic acid (AAS) in vivo reduced parasitemia and enhanced LPS-stimulated production of TNF by macrophages, but the effect was less in infected mice than in normal mice. Nevertheless, AAS treatment did not increase the susceptibility of infected mice to sublethal shock with LPS. Our results point to independent MIF and TNF/TNF-R1 lethal pathways and suggest a role for hyperactivated macrophages in T. cruzi-sensitized LPS-induced shock.     

Tumor necrosis factor-alpha from macrophages enhances LPS-induced clara cell expression of keratinocyte-derived chemokine

Tumor necrosis factor (TNF)-alpha is a cytokine produced by alveolar macrophages in response to LPS in the lung. Clara cells are bronchiolar epithelial cells that produce a variety of proinflammatory cytokines in response to LPS but not to TNF-alpha. In this study, we examined whether TNF-alpha affects Clara cell cytokine production in the setting of LPS stimulation. Using a transformed murine Clara cell line (C22), we observed that both LPS and TNF-alpha induced production of keratinocyte-derived chemokine (KC) and monocyte chemoattractant protein (MCP)-1. We also found that simultaneous LPS and TNF-alpha stimulation is synergistic for KC production, but additive for MCP-1 production. By using a Transwell coculture system of RAW264.7 macrophages and Clara cells isolated from C57Bl/6 mice, we found that macrophages produce a soluble factor that enhances Clara cell KC production in response to LPS. Cocultures of Clara cells from mice deficient in TNF-alpha receptors with RAW264.7 macrophages demonstrated that the effect of macrophages on Clara cells is mediated primarily via TNF-alpha. To determine whether these findings occur in vivo, we treated wild-type and TNF receptor-deficient mice intratracheally with LPS and examined the expression of KC. LPS-treated, TNF receptor-deficient mice showed much less KC mRNA in airway epithelial cells compared with wild-type mice. In contrast, a similar number of KC-expressing cells was seen in the lung periphery. Thus, upregulation of KC by Clara cells in the setting of LPS stimulation is largely dependent on TNF-alpha originating from alveolar macrophages. These findings shed light on macrophage-Clara cell interactions in regulating the pulmonary inflammatory response to LPS.     

Glycoinositolphospholipids from Trypanosoma cruzi interfere with macrophages and dendritic cell responses

To investigate the possible effects of glycoinositolphospholipid (GIPL) from Trypanosoma cruzi on human antigen presenting cells, we tested their effects on lipopolysaccharide (LPS)-stimulated human macrophages and dendritic cells (DC). Human macrophages or DC were incubated with GIPL (50 microg/ml) and LPS (500 pg/ml) and tumor necrosis factor alpha (TNF-alpha), interleukin 8 (IL-8), IL-10, and IL-12p40 levels in supernatants were analyzed by enzyme-linked immunosorbent assay. TNF-alpha, IL-10, and IL-12 secretion were significantly decreased by GIPL both in macrophages and DC. In contrast, GIPL did not alter IL-8 production. We also analyzed the expression of CD80, CD86, HLA-DR, CD40, and CD57 on the macrophage surface after stimulation with LPS in the presence or absence of T. cruzi GIPL. GIPL led to a down-regulation in the expression of all tested molecules. We additionally examined the influence of T. cruzi GIPL on the response of human DC to LPS. LPS-induced HLA-DR, CD83, and CD86 up-regulation was significantly inhibited by GIPL. A slight down-regulation in CD80 and CD40 expression on DC surfaces in the presence of GIPL was also noticed. Similarly, GIPL led to down-modulation of CD83, CD80, CD86, and HLA-DR surface expression and TNF-alpha and IL-10 production when DC were stimulated by CD40L. The ceramide portion of GIPL was responsible for most of the activity exhibited by the whole molecule. Considering the important role of the immune response in determining the fate of the host-parasite relationship, the immunoregulatory activities of T. cruzi GIPL are potentially important for parasite evasion and then pathogenesis of infection with protozoan parasites.     

Cytokine production by murine cells activated by erythrogenic toxin type A superantigen of Streptococcus pyogenes.

The mode of pathogenic action of the Steptococcus pyogenes superantigen erythrogenic toxin type A (ETA) in causing toxic shock-like syndrome in humans is thought to be mediated by massive release of cytokines by patients immune cells. The cytokine-inducing capacity of ETA as an extracellular protein was compared with that of lipopolysaccharide (LPS), a component of cell wall of gram-negative bacteria. Peritoneal macrophages and splenocytes of BALB/c and C3H/HeJ mice were stimulated by ETA and LPS. Tumor necrosis factor (TNF), interleukin 3 (IL-3) and interleukin 6 (IL-6) activities in the supernatants of stimulated cells were evaluated. In contrast to LPS, ETA induced only low amounts of IL-6 and no detectable TNF activities in peritoneal macrophage supernatants. ETA-triggered BALB/c and C3H/HeJ splenocytes produced great amounts of IL-6. ETA triggered the production of IL-3 by both mice strains splenocytes in a dose dependent manner. The amounts of IL-3 in supernatants were comparable to those induced by concanavalin A. The simultaneous presence of ETA and LPS in macrophage and splenocyte cultures induced a slight enhancement above an additive value after 72-96 h. Challenge of BALB/c mice with ETA 6 h before the harvest of peritoneal macrophages led to an enhanced production of IL-6 upon stimulation with ETA as well as with LPS. Splenocytes of nude BALB/c mice did not produce IL-6 upon stimulation with ETA, whereas LPS-induced IL-6 production was similar in these mice and in their littermates. The pathogenic effect of ETA on host's immune cells could most likely be explained as a consequence of T cell activation. The results confirm also that LPS- and ETA-induced shock is mediated by different cell types.     

Commensal microbiota induce LPS hyporesponsiveness in colonic macrophages via the production of IL-10

Several subsets of innate immune cells, all with unique properties, reside within the intestinal lamina propria. However, compared with intestinal dendritic cells (DCs), intestinal macrophages are less well characterized. In this study, we examined the properties of macrophages in the colonic lamina propria (LMφ). Colonic DCs (LDC) showed LPS-induced production of IL-12p40. In contrast, LMφ showed constitutive IL-10 production and unresponsiveness to LPS in terms of inflammatory cytokine production. Comparison of the gene expression profiles between LMφ and LDC revealed that LMφ preferentially expressed IL-10-related genes. LMφ obtained from mice lacking IL-10 or Stat3 showed hyperproduction of tumour necrosis factor (TNF)-α and IL-6 in response to LPS. IL-10 production in the large intestine was mainly induced by LMφ and regulatory T cells and was dependent on the presence of commensal microbiota. Accordingly, LMφ from germ-free mice showed less production of IL-10 and increased levels of LPS-induced TNF-α and IL-6 production. Taken together, these results demonstrate that the activity of LMφ to produce pro-inflammatory cytokines is negatively regulated through commensal microbiota-dependent IL-10 production in the large intestine.     

Differential regulation of lipopolysaccharide and Gram-positive bacteria induced cytokine and chemokine production in macrophages by Galpha(i) proteins

Heterotrimeric G(i) proteins play a role in signalling activated by lipopolysaccharide (LPS), Staphylococcus aureus (SA) and group B streptococci (GBS), leading to production of inflammatory mediators. We hypothesized that genetic deletion of G(i) proteins would alter cytokine and chemokine production induced by LPS, SA and GBS stimulation. LPS-induced, heat-killed SA-induced and heat-killed GBS-induced cytokine and chemokine production in peritoneal macrophages from wild-type (WT), Galpha(i2) (-/-) or Galpha(i1/3) (-/-) mice were investigated. LPS induced production of tumour necrosis factor-alpha (TNF-alpha), interleukin-6 (IL-6), IL-10 and interferon-gamma-inducible protein-10 (IP-10); SA induced TNF-alpha, and IL-1beta production; and GBS induced TNF-alpha, IL-6, IL-1beta, macrophage inflammatory protein-1alpha (MIP-1alpha) and keratinocyte chemoattract (KC) production were all decreased (P < 0.05) in Galpha(i2) (-/-) or Galpha(i1/3) (-/-) mice compared with WT mice. In contrast to the role of G(i) proteins as a positive regulator of mediators, LPS-induced production of MIP-1alpha and granulocyte-macrophage colony-stimulating factor (GM-CSF) were increased in macrophages from Galpha(i1/3) (-/-) mice, and SA-induced MIP-1alpha production was increased in both groups of Galpha(i) protein-depleted mice. LPS-induced production of KC and IL-1beta, SA-induced production of GM-CSF, KC and IP-10, and GBS-induced production of IL-10, GM-CSF and IP-10 were unchanged in macrophages from Galpha(i2) (-/-) or Galpha(i1/3) (-/-) mice compared with WT mice. These data suggest that G(i2) and G(i1/3) proteins are both involved and differentially regulate murine inflammatory cytokine and chemokine production in response to both LPS and Gram-positive microbial stimuli.