T-cell-mediated activation of macrophages

Inducible NOS-induced chloride intracellular channel 4 (CLIC4) nuclear translocation regulates macrophage deactivation

Nuclear translocation of cytosolic CLIC4 is an essential feature of its proapoptotic and prodifferentiation functions. Here we demonstrate that CLIC4 is induced concurrently with inducible nitric oxide synthase (iNOS) and S-nitrosylated in proinflammatory peritoneal macrophages. Chemical inhibition or genetic ablation of iNOS inhibits S-nitrosylation and nuclear translocation of CLIC4. In macrophages, iNOS-induced nuclear CLIC4 coincides with the pro- to anti-inflammatory transition of the cells because IL-1β and CXCL1 mRNA remain elevated in CLIC4 and iNOS knockout macrophages at late time points, whereas TNFα mRNA is elevated only in the iNOS knockout macrophages. Active IL-1β remains elevated in CLIC4 knockout macrophages and in macrophages in which CLIC4 nuclear translocation is prevented by the NOS inhibitor l-NAME. Moreover, overexpression of nuclear-targeted CLIC4 down-regulates IL-1β in stimulated macrophages. In mice, genetically null for CLIC4, the number of phagocytosing macrophages stimulated by LPS is reduced. Thus, iNOS-induced nuclear CLIC4 is an essential part of the macrophage deactivation program.

Enhanced induction of LPS-induced fibroblast MCP-1 by interferon-gamma: involvement of JNK and MAPK phosphatase-1

IFN-gamma has significant immunoregulatory activity and plays an important role in both innate and adaptive immunity. Additive effects of IFN-gamma and the Toll-like receptor ligand LPS has been investigated in macrophages, but in fibroblasts is incompletely understood. IFN-gamma and LPS synergistically induced MCP-1 and NO release in primary murine dermal fibroblasts. IFN-gamma enhanced LPS-induced JNK and p38 MAPK phosphorylation but had no effect on NF-kappaB activity. The induction of both MCP-1 and NO was attenuated by inhibition of JNK but not p38 MAPK. Serine 727 STAT1 phosphorylation by IFN-gamma was increased by LPS, and this was also attenuated by inhibition of JNK but not p38 MAPK. IFN-gamma inhibited the basal expression of MAPK phosphatase-1, a negative regulator of MAPK signaling pathway. These results suggest that enhancement of LPS-induced JNK activation by IFN-gamma associated with inhibition of MAPK phosphatase-1 may be one of the mechanisms of additive effects between IFN-gamma and LPS in fibroblasts.

The Herpes simplex virus gene Pol expressed in herpes-associated erythema multiforme lesions upregulates/activates SP1 and inflammatory cytokines

BACKGROUND/AIMS

Herpes-simplex-virus-associated erythema multiforme (HAEM) is characterized by lesional skin expression of the viral protein Pol and localized inflammation. The objective of this study is to examine the mechanism whereby Pol induces localized inflammation.

METHODS

A431 cells transfected with Pol or an empty vector and lesional skin from HAEM or drug-induced erythema multiforme patients were examined for expression of the transcription factor SP1 and SP1-regulated genes by immunoblotting, immunohistochemistry and immunofluorescence.

RESULTS

SP1, TGF-beta, p21(waf1) and Hsp27 were upregulated in A431 cells transfected with Pol but not the empty vector. Expression was further increased by exposure to IFN-gamma. Pol+ HAEM lesional skin expressed SP1, Hsp27, TGF-beta and p21(waf1). Normal skin and drug-induced erythema multiforme lesional skin were negative.

CONCLUSION

The data indicate that Pol activates SP1, causing upregulation of SP1 target genes (notably TGF-beta) involved in localized inflammation. Upregulation is potentiated by IFN-gamma.

Microtubules regulate PI-3K activity and recruitment to the phagocytic cup during Fcgamma receptor-mediated phagocytosis in nonelicited macrophages

Phagocytosis is a complex sequence of events involving coordinated remodeling of the plasma membrane with the underlying cytoskeleton. Although the role of the actin cytoskeleton is becoming increasingly elucidated, the role of microtubules (MTs) remains poorly understood. Here, we examine the role of MTs during FcgammaR-mediated phagocytosis in RAW264.7 mouse macrophages. We observe that MTs extend into the phagosomal cups. The MT-depolymerizing agents, colchicine and nocodazole, cause a sizeable reduction in phagocytosis of large particles in RAW264.7 cells. Phagocytosis in primed macrophages is unaffected by MT-depolymerizing agents. However, activation of macrophages coincides with an increased population of drug-stable MTs, which persist in functional phagocytic cups. Scanning electron microscopy analysis of unprimed macrophages reveals that pseudopod formation is reduced markedly following colchicine treatment, which is not a consequence of cell rounding. MT depolymerization in these cells does not affect particle binding, Syk, or Grb2-associated binder 2 recruitment or phosphotyrosine accumulation at the site of phagocytosis. Ras activation also proceeds normally in macrophages treated with colchicine. However, MT disruption causes a decrease in accumulation of AKT-pleckstrin homology-green fluorescent protein, a probe that binds to PI-3K products at the sites of particle binding. A corresponding decline in activated AKT is observed in colchicine-treated cells using immunoblotting with a phospho-specific-AKT (ser473) antibody. Furthermore, the translocation of the p85alpha regulatory subunit of PI-3K is reduced at the phagocytic cup in colchicine-treated cells. These findings suggest that MTs regulate the recruitment and localized activity of PI-3K during pseudopod formation.

The role of the activated macrophage in clearing Listeria monocytogenes infection

Macrophage activation often contributes to the strong immune response elicited upon infection. The ability of macrophages to become activated was discovered when sub-lethal primary infections of mice with the bacterium Listeria monocytogenes provided protection against secondary infections through non-humoral immunity. L. monocytogenes infect and propagate in macrophages by escaping the phagosome into the cytosol, where they avoid humoral immune mediators. Activated macrophages kill L. monocytogenes by blocking phagosomal escape. The timing of the antimicrobial activities within the phagosome is crucial to the outcome. In non-activated macrophages, bacterial factors generally prevail, and L. monocytogenes can escape from the vacuoles and grow within cytoplasm. Activated macrophages generate reactive oxygen or nitrogen intermediates early after bacterial uptake, which prevent the bacteria from escaping vacuoles into cytoplasm. The heterogeneity in the interactions between L. monocytogenes and the macrophage indicate a complex relationship between the host and the pathogen governed by chemistries that promote and inhibit escape from vacuoles. This review examines the mechanisms used by activated and non-activated macrophages to kill microbes, and how those mechanisms are employed against L. monocytogenes.

Salmonella typhimurium persists within macrophages in the mesenteric lymph nodes of chronically infected Nramp1+/+ mice and can be reactivated by IFNgamma neutralization

Host-adapted strains of Salmonella are capable of establishing a persistent infection in their host often in the absence of clinical disease. The mouse model of Salmonella infection has primarily been used as a model for the acute systemic disease. Therefore, the sites of long-term S. typhimurium persistence in the mouse are not known nor are the mechanisms of persistent infection clearly understood. Here, we show that S. typhimurium can persist for as long as 1 yr in the mesenteric lymph nodes (MLNs) of 129sv Nramp1^+/+ (Slc11a1^+/+) mice despite the presence of high levels of anti–S. typhimurium antibody. Tissues from 129sv mice colonized for 60 d contain numerous inflammatory foci and lesions with features resembling S. typhi granulomas. Tissues from mice infected for 365 d have very few organized inflammatory lesions, but the bacteria continue to persist within macrophages in the MLN and the animals generally remain disease-free. Finally, chronically infected mice treated with an interferon-γ neutralizing antibody exhibited symptoms of acute systemic infection, with evidence of high levels of bacterial replication in most tissues and high levels of fecal shedding. Thus, interferon-γ, which may affect the level of macrophage activation, plays an essential role in the control of the persistent S. typhimurium infection in mice.

Recruitment of IFN-gamma-producing (Th1-like) cells into the inflamed retina in vivo is preferentially regulated by P-selectin glycoprotein ligand 1:P/E-selectin interactions

Although there is evidence that altering the Th1/Th2 balance toward Th2 cells may be important in the resolution of Th1-type autoimmune disease, adoptive transfer of Th2 cells is not effective in protecting against Th1-type disease and may cause disease. Therefore, we examined the recruitment of Th1- and Th2-like cells into the retina in the murine autoimmune disease experimental autoimmune uveoretinitis. CD4 T cells were polarized in vitro to IFN-gamma-producing Th1-like cells and non-IFN-gamma-producing Th2-like cells, labeled, and adoptively transferred. Trafficking to the retina in vivo was evaluated by scanning laser ophthalmoscopy and infiltration by confocal microscopy. There were more rolling and adherent Th1-like cells and they rolled more slowly than did Th2-like cells. Th1-like cells were preferentially recruited into the retinal parenchyma at both initiation and resolution. Surface P-selectin glycoprotein ligand 1 (PSGL-1) and LFA-1 were up-regulated on both populations but were expressed at higher levels on Th1-like cells. Up-regulation of CD44 expression was higher on Th2-like cells. P-selectin, E-selectin, and ICAM-1 are up-regulated on postcapillary venules in the retina. Pretreatment of Th1-like cells with anti-PSGL-1 inhibited rolling and infiltration of Th1-like cells but not Th2-like cells, providing direct in vivo evidence for the inability of Th2 to respond to P/E-selectin despite increased expression of PSGL-1. Anti-LFA-1 pretreatment inhibited infiltration of both Th1- and Th2-like cells, but more so Th-1. We suggest that random trafficking of activated T cells (both Th1 and Th2) across the blood-retina barrier is mediated by CD44:CD44R and LFA-1:ICAM-1, whereas preferential recruitment of Th1 cells is mediated by PSGL-1:P/E-selectin.

Tools for anti-inflammatory drug design:In vitro models of leukocyte migration

Inhibiting leukocyte recruitment is now a major focus in the design of novel anti-inflammatory drugs. Following the identification of lead compounds from conventional high-throughput screens using appropriate receptors or enzymes, it is important to validate the action of the compounds in a suitable in vitro model of leukocyte migration. Here, we review a range of different experimental approaches to modelling leukocyte migration, and identify the multi-well filter migration assay as the best compromise between the amount of resources required to screen multiple compounds and the amount of information gained about the effects of the compounds on cell movement behavior. However, there are pitfalls in the interpretation of data obtained using the multi-well filter migration assay, which arise from the imperfect correlation between the number of cells undergoing migration and the inhibitory activity of the test substances. We examine a number of such pitfalls and provide practical approaches to mitigate these problems as far as possible. We recommend a general strategy for screening inhibitors of cell migration using in vitro functional assays. While being more resource intensive than surrogate measures such as calcium flux, functional approaches nevertheless provide superior correlations with anti-inflammatory activity in vivo.

p38 MAPK enhances STAT1-dependent transcription independently of Ser-727 phosphorylation

The transcription factor signal transducer and activator of transcription 1 (STAT1) requires phosphorylation at both Tyr-701 and Ser-727 for full activation. IFN-gamma induces phosphorylation of both residues, whereas stress signals like UV or lipopolysaccharide stimulate phosphorylation of Ser-727 only. Using p38alpha mitogen-activated protein kinase (MAPK)-deficient cells, we show that the stress-induced phosphorylation of Ser-727 requires p38alpha MAPK activity, whereas IFN-gamma-stimulated Ser-727 phosphorylation occurs independently of the p38alpha pathway. Consistently, IFN-gamma stimulated expression of the STAT1 target gene IRF1 to a similar extent in both wild-type and p38alpha-deficient cells. However, stress-induced activation of the p38 MAPK pathway considerably enhanced the IFN-gamma-induced expression of both the endogenous IRF1 gene and a reporter driven by the IFN-gamma-activated sequence element of the IRF1 promoter. This enhancement occurred independently of increased phosphorylation of Ser-727 by the p38 pathway. Taken together, these results demonstrate an interaction between IFN-gamma signaling and the p38 pathway that leads to increased transcriptional activation by STAT1 independently of phosphorylation at Ser-727.

Gamma interferon down-regulates Fer and induces its association with inactive Stat3 in colon carcinoma cells

Gamma interferon (IFN-gamma) is a regulator of cell growth, which suppresses the proliferation of HT-29 colon carcinoma cells. Here we show that in HT-29 cells IFN-gamma transiently increased the cellular level of the tyrosine kinase Fer, whose functioning was found to be essential for the proliferation of malignant cell-lines. The transient elevation in the level of Fer, was followed by its down-regulation, an effect which was most prominent after 6-8 h of IFN-gamma treatment. Up- and down-regulation of Fer was paralleled by the activation and subsequent deactivation of Stat3, which is a potent oncogene and a putative substrate of the tyrosine kinase Fer. Moreover, IFN-gamma induced the association of Fer and Stat3 and the newly formed complex was most stable at the down-regulated states of the two proteins. Formation of the Fer/Stat3 complex was accompanied by an attenuation in cell-cycle progression and accumulation of cells in the G1 phase. Thus, Fer and Stat3 are two proliferation-promoting factors whose down-regulation could contribute to the cytostatic activity of IFN-gamma in colon carcinoma cells.

The Stat1 binding motif of the interferon-gamma receptor is sufficient to mediate Stat5 activation and its repression by SOCS3

Signal transduction via the interferon-gamma (IFN-gamma) receptor requires the tyrosine phosphorylation of signal transducers and activators of transcription (Stats). Whereas tyrosine phosphorylation of Stat1 occurs in all cells, activation of Stat5 by IFN-gamma is cell type-restricted. Here we investigated the mechanism of Stat5 activation by the IFN-gamma receptor. In transfection assays both Stat5 isoforms, Stat5a and Stat5b, were phosphorylated on tyrosine in response to IFN-gamma. Stat5 activation required the presence of tyrosine 420 (Tyr-420) in the murine IFNGR1 receptor chain, which also serves as the Stat1 binding site. Moreover, a peptide including Tyr-440, the Stat1 binding site of the human IFNGR1 chain, conferred the ability upon a synthetic receptor to activate Stat5. Suppressor of cytokine signaling 3 (SOCS3) inhibited the activation of Stat5 by the IFN-gamma receptor, and the Tyr-440-containing peptide stretch was sufficient for repression. SOCS3 expression had little effect on the activity of Jak kinases not associated with cytokine receptors. In IFN-gamma-treated, Stat1-deficient fibroblasts Stat5 was inefficient in inducing transcription of a Stat-dependent reporter gene, suggesting it does not per se make a major contribution to the expression of IFN-gamma-responsive genes.

Identification of a phorbol ester-responsive element in the interferon-gamma receptor 1 chain gene

Human monocytic leukemia THP-1 cells differentiate into macrophage-like cells when treated with 12-O-tetradecanoylphorbol-13-acetate (TPA). During this process, interferon-gamma (IFN-gamma)-inducible expression of human leukocyte antigen-DR alpha is markedly enhanced. The enhancement of human leukocyte antigen-DR alpha expression is at least due to the TPA-dependent induction of the IFN-gamma receptor 1 chain and IFN-gamma receptor 2 chain genes. Here we have studied the mechanism of TPA-induced up-regulation of the IFN-gamma receptor 1 chain gene. Reporter gene analyses of 5'-deletion constructs of the IFN-gamma receptor 1 gene (IFNGR1) promoter indicated that the critical region for control of transcription and the TPA-responsive element (TRE) were present in the -128 to -109 base pair (bp) region. We confirmed that this region of the IFNGR1 promoter was responsive to TPA-induced signals by using a reporter construct whose promoter consisted of the -128 to -109 bp fragment and the minimal herpes simplex virus thymidine kinase promoter. Moreover, a supershift assay indicated that Sp1 bound to this TRE in TPA-treated THP-1 cells. These results suggest that in TPA-treated cells the binding of Sp1 to the TRE of the IFNGR1 promoter causes the up-regulation of this gene.

The other side of the coin: the protective role of the TH2 cytokines

Although T(H)2 cytokine involvement in allergy makes these cytokines attractive therapeutic targets, they protect against ectoparasites and gastrointestinal worms and suppress inflammation induced by T(H)1 cytokines. T(H)2 cytokines induce mastocytosis, eosinophilia, IgE synthesis, and mucus production. Each element of this response protects against some worms; however, different worms are protected against by different elements of the total response. The induction of the entire response by most parasitic worms suggests that it is safer for the immune system to make a stereotyped worm-protective response than to attempt to match a more specific response to a particular worm. In contrast, the reciprocal antagonism between T(H)1 and T(H)2 cytokines suggests that it is safer for the immune system to limit immunopathology by suppressing inflammatory effector mechanisms not required for host protection against a particular pathogen class than to make an all-purpose inflammatory response. This, in turn, implies that innate immunity can distinguish different classes of parasites (eg, worms vs protozoa) but has limited ability to distinguish individual parasites within a class (eg, different worms). Although these considerations suggest that T(H)2 cytokine antagonists may increase the risk and severity of worm infections and T(H)1 cytokine-mediated inflammatory disorders, such therapy should be relatively safe if it is restricted to areas in which worm infections are rare and commonsense precautions are taken to minimize the risk of inducing T(H)1 cytokine-related inflammatory disease.

Transforming growth factor-beta suppresses interferon-gamma-induced toxoplasmastatic activity in murine macrophages by inhibition of tumour necrosis factor-alpha production

Activation of macrophages plays an important role in the host resistance against intracellular pathogens. Various mechanisms are employed to control the activation processes and limit tissue damage by factors produced by activated macrophages. One of these mechanisms is the production of macrophage-deactivating cytokines, such as tumour growth factor (TGF)-beta. The present study concerns the effects of TGF-beta on interferon (IFN)-gamma-induced activation of murine macrophages with respect to induction of toxoplasmastatic activity, and production of tumour necrosis factor (TNF)-alpha, prostaglandin E2 (PGE2) and reactive nitrogen intermediates (RNI). IFN-gamma activation of macrophages resulted in inhibition of T. gondii proliferation [mean fold increase (FI) = 1.8, control mean FI = 7.0]; polymyxin B had no effect on this activation. The IFN-gamma-induced toxoplasmastatic activity of macrophages was inhibited by TGF-beta (mean FI = 6.3), which was also found for the IFN-gamma-induced production of TNF-alpha, RNI and PGE2 by macrophages. We found that PGE2, which has macrophage deactivating properties, was not involved in the inhibition of macrophage activation by TGF-beta. The deactivating activities of TGF-beta on the IFN-gamma-induced toxoplasmastatic activity and production of RNI are mediated by inhibition of production of TNF-alpha. Addition of exogenous TNF-alpha during the incubation of macrophages with IFN-gamma and TGF-beta abrogated the deactivating activity of TGF-beta. In sum, the results demonstrate that inhibition of TNF-alpha production is a key factor in the TGF-beta-induced suppression of macrophage activation with respect to toxoplasmastatic activity and RNI production.

Cytokine regulation of host defense against parasitic gastrointestinal nematodes: lessons from studies with rodent models

Studies with rodents infected with Trichinella spiralis, Heligmosomoides polygyrus, Nippostronglyus brasiliensis, and Trichuris muris have provided considerable information about immune mechanisms that protect against parasitic gastrointestinal nematodes. Four generalizations can be made: 1. CD4+ T cells are critical for host protection; 2. IL-12 and IFN-gamma inhibit protective immunity; 3. IL-4 can: (a) be required for host protection, (b) limit severity of infection, or (c) induce redundant protective mechanisms; and 4. Some cytokines that are stereotypically produced in response to gastrointestinal nematode infections fail to enhance host protection against some of the parasites that elicit their production. Host protection is redundant at two levels: 1. IL-4 has multiple effects on the immune system and on gut physiology (discussed in this review), more than one of which may protect against a particular parasite; and 2. IL-4 is often only one of multiple stimuli that can induce protection. Hosts may have evolved the ability to recognize features that characterize parasitic gastrointestinal nematodes as a class as triggers for a stereotypic cytokine response, but not the ability to distinguish features of individual parasites as stimuli for more specific protective cytokine responses. As a result, hosts deploy a set of defense mechanisms against these parasites that together control infection by most members of that class, even though a specific defense mechanism may not be required to defend against a particular parasite and may even damage a host infected with that parasite.

Molecular fingerprint of interferon-gamma signaling in unstable angina

BACKGROUND

Activation of circulating monocytes in patients with acute coronary syndromes may reflect exposure to bacterial products or stimulation by cytokines such as IFN-gamma. IFN-gamma induces phosphorylation and nuclear translocation of transcription factor STAT-1, which initiates a specific program of gene induction. To explore whether monocyte activation is IFN-gamma driven, patients with unstable (UA) or stable angina (SA) were compared for nuclear translocation of STAT-1 complexes and upregulation of IFN-gamma-inducible genes CD64 and IP-10.

METHODS AND RESULTS

Peripheral blood mononuclear cells were stained for expression of CD64 on CD14(+) monocytes and analyzed by PCR for transcription of IP-10. Expression of CD64 was significantly increased in patients with UA. Monocytes from UA patients remained responsive to IFN-gamma in vitro, with accelerated transcriptional competency of CD64. IP-10-specific sequences were spontaneously detectable in 82% of the UA patients and 15% of SA patients (P<0.001). Most importantly, STAT-1 complexes were found in nuclear extracts prepared from freshly isolated monocytes of patients with UA, which provides compelling evidence for IFN-gamma signaling in vivo.

CONCLUSIONS

Monocytes from UA patients exhibit a molecular fingerprint of recent IFN-gamma triggering, such as nuclear translocation of STAT-1 complexes and upregulation of IFN-gamma-inducible genes CD64 and IP-10, which suggests that monocytes are activated, at least in part, by IFN-gamma. IFN-gamma may derive from stimulated T lymphocytes, which implicates specific immune responses in the pathogenesis of acute coronary syndromes.

Role of T cells and gamma interferon during induction of hypersensitivity to lipopolysaccharide by toxic shock syndrome toxin 1 in mice

The superantigenic function of toxic shock syndrome toxin 1 (TSST-1) is generally regarded as an important determinant of its lethal effects in humans or experimental animals. This study examined the role of superantigenicity in a BALB/c mouse model of lethal TSST-1-induced hypersensitivity to lipopolysaccharide (LPS). In this model, TSST-1 greatly potentiated both LPS-induced lethality, as well as LPS-induced serum tumor necrosis factor alpha (TNF-alpha) activity. Although BALB/c-SCID mice were resistant to these LPS enhancement effects of TSST-1, BALB/c-SCID mice reconstituted with T cells were completely susceptible to the enhancement effect of TSST-1 on LPS-induced serum TNF-alpha. Mice pretreated with cyclosporine (Cs) or neutralizing antibodies against gamma interferon (IFN-gamma) did not develop lethal LPS hypersensitivity when injected with TSST-1, and these agents reduced the enhancement effect of TSST-1 on LPS-induced serum TNF-alpha by 99 and 85%, respectively. Cs pretreatment also completely inhibited the known capacity of TSST-1 to amplify LPS-induced levels of IFN-gamma in serum. In contrast, mice given Cs after a priming injection of TSST-1, but before LPS, still exhibited lethal hypersensitivity to LPS. Cs given after TSST-1 also did not inhibit enhancement of LPS-induced serum TNF-alpha by TSST-1 but inhibited the enhancement effect of TSST-1 on LPS-induced serum IFN-gamma by 50%. These experiments support the theory that TSST-1-induced hypersensitivity to LPS is mediated primarily by IFN-gamma derived from superantigen-activated T cells.

A distinct expression of CC chemokines by macrophages in nasopharyngeal carcinoma: implication for the intense tumor infiltration by T lymphocytes and macrophages

Nasopharyngeal carcinoma (NPC) is characterized by harboring Epstein-Barr virus genes in the tumor cells and an intense infiltration of leukocytes in the tumor tissue. These infiltrating cells are mainly composed of T lymphocytes and macrophages. The mechanism of this intense infiltration has long been a puzzle. We attempted to address this issue by studying the expression of CC chemokines, which are responsible for recruiting both T cells and macrophages, by an immunohistochemical approach. In biopsies obtained from nasopharynx of 17 NPC patients that contained tumor cells, expression of macrophage inflammatory protein 1alpha (MIP-1alpha), MIP-1beta, macrophage chemoattractant protein-1 (MCP-1), MCP-2, MCP-3, and RANTES was detected in the tumor-infiltrating cells, with MIP-1alpha and MCP-1 found in nearly all biopsies and the others relatively less frequently. Furthermore, expression of interferon-gamma (IFN-gamma) was also observed in tumor-infiltrating cells. In contrast, CC chemokines and IFN-gamma were rarely expressed in the 13 control biopsies that were either normal or with nonspecific inflammation, and in 4 biopsies from untreated NPC patients that contained no tumor cells. Using an immunofluorescent double-staining method, MIP-1alpha and MCP-1 were identified to be associated with macrophages, and IFN-gamma with T cells. Moreover, expression of CCR2 and CCR5, the receptors for these chemokines, was also detected in the tumor-infiltrating cells. These data indicate that the intense tumor infiltration by T cells and macrophages is a result of active recruitment. It seems possible that the intense infiltration of leukocytes in NPC tumor tissue is initiated by the activated tumor-reactive T cells. T cells migrate into the tumor tissue in an antigen-specific mode, and IFN-gamma secreted from these pioneer T cells activates tissue macrophages to express CC chemokines, especially MIP-1alpha and MCP-1, which consequently recruit more T cells and macrophages into the tumor tissue.

Listeria monocytogenes modulates macrophage cytokine responses through STAT serine phosphorylation and the induction of suppressor of cytokine signaling 3

Macrophage activation as part of natural resistance to infection is caused by stimulation with IFN-gamma and by the invading microorganisms or microbial products. Infection of macrophages with the Gram-positive bacterium Listeria monocytogenes for short periods before activation with IFN-gamma increased the phosphorylation of transcription factor STAT1 at S727 and thereby the expression of IFN-gamma-induced genes. By contrast, persistent infection with viable bacteria or treatment with heat-killed Listeria diminished IFN-gamma-stimulated transcription and the phosphorylation of STAT1 at Y701. Decreased IFN-gamma signaling correlated with the induction of suppressor of cytokine signaling 3 (SOCS3) mRNA and protein. Contrasting our previous findings with LPS, maximal synthesis of SOCS3 required both the immediate signals from Listeria receptors on the cell surface and the activity of a polypeptide secreted in response to bacterial infection. SOCS3 induction by the secreted protein could not be blocked by neutralizing Abs to IL-10 and it did not require the presence of STAT1. Consistent with the induction of SOCS3 activity, Listeria also inhibited activation of STAT5 by GM-CSF. The p38 mitogen-activated protein kinase was rapidly activated upon infection of macrophages with L. monocytogenes. Inhibition of p38 mitogen-activated protein kinase with the pyridinyl imidazol SB203580 abrogated both STAT1 S727 phosphorylation and the expression of SOCS3. The data suggest that STAT1 serine kinase and SOCS3 activity are hallmarks of immediate and delayed phases of influence by bacterial signals on signal transduction in response to IFN-gamma.

CD8(+) T cell knockout mice are less susceptible to Cowdria ruminantium infection than athymic, CD4(+) T cell knockout, and normal C57BL/6 mice

The role of T cells in immunity to Cowdria ruminantium was investigated by studying the responses to infection of normal, athymic, CD4(+) T cell knock out (KO) and CD8(+) T cell KO C57BL/6 mice. Normal C57BL/6 mice could be immunized by infection and treatment, and immunity was adoptively transferable from immune to naive mice by splenocytes. Following infection, athymic mice died sooner than normal mice (P=0.0017), and could not be immunized by infection and treatment. CD4(+) T cell KO mice were as susceptible to infection as normal mice and could be immunized by infection and treatment. In contrast, CD8(+) T cell KO mice were less susceptible than normal and CD4(+) T cell KO mice and 43% self-cured, while those that died did so after a prolonged incubation period. Antibody responses to C. ruminantium were CD4(+) T cell dependent, because responses were detected in immune normal and CD8(+) T cell KO mice but not in immune CD4(+) KO mice (P=0.005). Since CD8(+) T cell KO mice were less susceptible to infection, and since CD4(+) T cell KO mice could be immunized, it can be concluded that immunity to C. ruminantium can be mediated by both CD4(+) and CD8(+) T cells.

A polarized Th1 type immune response to Cowdria ruminantium infection is detected in immune DBA/2 mice

Immune responses to Cowdria ruminantium, an intracellular organism that causes heartwater in domestic ruminants, were characterized in a DBA/2 mouse model. Immunity induced by infection and treatment was adoptively transferable by splenocytes and could be abrogated by in vivo depletion of T cells but not by inhibition of nitric oxide synthase using NG-monomethyl-L-arginine. IgG2a and IgG2b C. ruminantium-specific responses were detected in immune mice. Culture supernatants of splenocytes from immune DBA/2 mice, which were stimulated with crude C. ruminantium antigens or recombinant major antigenic proteins 1 or 2, contained significant levels of interferon (IFN)-gamma and interleukin (IL)-6, but insignificant levels of IL-1alpha, IL-2, IL-4, IL-5, IL-10, IL-12, tumor necrosis factor-alpha (TNF), and nitric oxide. A similar response was detected during primary infection, although IFN-gamma levels decreased significantly during clinical illness and then increased following natural or antibiotic-aided recovery. These data support the conclusion that protective immunity to C. ruminantium in DBA/2 mice is mediated by T cells and is associated with a polarized T helper 1 type of immune response. This murine model could be utilized to screen for protective C. ruminantium antigens that provoke Th1 type immune responses and for evaluation of these antigens in recombinant vaccines against heartwater.

Cooperation among Stat1, glucocorticoid receptor, and PU.1 in transcriptional activation of the high-affinity Fc gamma receptor I in monocytes

IFN-gamma and glucocorticoids regulate inflammatory and immune responses through Stat1 and glucocorticoid receptor (GR) transcription factors, respectively. The biological responses to these polypeptides are determined by integration of various signaling pathways in a cell-type and promoter-dependent manner. In this study we have characterized the molecular basis for the functional cooperation between IFN-gamma and dexamethasone (Dex) in the induction of the high-affinity Fc gamma receptor I (Fc gamma RI) in monocytes. Dex did not affect IFN-gamma-induced Stat1 DNA binding activity or induce novel DNA-binding complexes to the Fc gamma RI promoter. By using cell systems lacking functional GR or Stat1, we showed that GR stimulated Stat1-dependent transcription in a ligand-dependent manner, while Stat1 did not influence GR-dependent transcription. The cooperation required phosphorylation of Tyr701, DNA binding, and the trans-activation domain of Stat1, but did not involve Ser727 phosphorylation of Stat1 or physical interaction between GR and Stat1. The costimulatory effect of Dex was not dependent on a consensus glucocorticoid response element in the Stat1-responsive promoters, but required the DNA-binding and trans-activation functions of GR, and Dex-induced protein synthesis. GR activated the natural Fc gamma RI promoter construct, and this response required both Stat1 and the Ets family transcription factor PU.1. Previously, physical association between GR and Stat5 has been shown to enhance Stat5-dependent and suppress GR-dependent transcription. The results shown here demonstrate a distinct, indirect mechanism of cross-modulation between cytokine and steroid receptor signaling that integrates Stat1 and GR pathways with cell type-specific PU.1 transcription factor in the regulation of Fc gamma RI gene transcription.

Stat6 signaling promotes protective immunity against Trichinella spiralis through a mast cell- and T cell-dependent mechanism

Studies in mice infected with the gastrointestinal nematode parasite Nippostrongylus brasiliensis demonstrated that IL-4/IL-13 activation of Stat6 suppresses development of intestinal mastocytosis and does not contribute to IL-4/IL-13 production, but is still essential for parasite expulsion. Because expulsion of another gastrointestinal nematode, Trichinella spiralis, unlike N. brasiliensis expulsion, is mast cell dependent, these observations suggested that T. spiralis expulsion would be Stat6 independent. Instead, we find that Stat6 activation by IL-4/IL-13 is required in T. spiralis-infected mice for the mast cell responses that induce worm expulsion and for the cytokine responses that induce intestinal mastocytosis. Furthermore, although IL-4 induces N. brasiliensis expulsion in the absence of B cells, T cells, and mast cells, mast cells and T cells are required for IL-4 induction of T. spiralis expulsion. Thus, Stat6 signaling is required for host protection against N. brasiliensis and T. spiralis but contributes to expulsion of these two worms by different mechanisms. The induction of multiple effector mechanisms by Stat6 signaling provides a way for a cytokine response induced by most gastrointestinal nematode parasites to protect against most of these parasites, even though different effector mechanisms are required for protection against different nematodes.

Herpes simplex virus associated erythema multiforme (HAEM) is mechanistically distinct from drug-induced erythema multiforme: interferon-gamma is expressed in HAEM lesions and tumor necrosis factor-alpha in drug-induced erythema multiforme lesions

Erythema multiforme follows administration of several drugs or infection with various agents, including herpes simplex virus, a syndrome designated herpes simplex virus associated erythema multiforme. Lesional skin from 21 of 26 (81%) herpes simplex virus associated erythema multiforme patients was positive for herpes simplex virus gene expression as evidenced by reverse transcriptase-polymerase chain reaction with primers for DNA polymerase and/or immunohistochemistry with DNA polymerase antibody. Reverse transcriptase-polymerase chain reaction and immunohistochemistry studies indicated that herpes simplex virus associated erythema multiforme lesional skin from 16 of 21 (76%) DNA polymerase positive herpes simplex virus associated erythema multiforme patients was also positive for interferon-gamma, a product of T cells involved in delayed-type hypersensitivity (p < 0. 0001 by Pearson correlation coefficient). Interferon-gamma signals were in infiltrating mononuclear cells and in intercellular spaces within inflammatory sites in the epidermis and at the epidermis/dermis junction. Herpes simplex virus lesional skin was also positive for DNA polymerase [five of five (100%)] and interferon-gamma [four of five (80%)], but lesional skin from drug-induced erythema multiforme patients was negative. Lesional herpes simplex virus associated erythema multiforme keratinocytes also stained with antibody to transforming growth factor-beta [14 of 23 (61%)] and cyclin-dependent kinase inhibitor waf [12 of 18 (67%)]. Staining was also seen in keratinocytes from herpes simplex virus lesions [five of five (100%)], but not in normal skin. By contrast, staining with antibody to tumor necrosis factor-alpha, another pro-inflammatory cytokine, was seen in seven of 11 (64%) drug-induced erythema multiforme patients, but not in herpes simplex virus or herpes simplex virus associated erythema multiforme patients, and lesional keratinocytes from drug-induced erythema multiforme patients were negative for transforming growth factor-beta and cyclin-dependent kinase inhibitor waf. We interpret the data to indicate that herpes simplex virus associated erythema multiforme pathology includes a delayed-type hypersensitivity component and is mechanistically distinct from drug-induced erythema multiforme.

Inhibition of macrophage activity by mitogen-induced goldfish leukocyte deactivating factor

Macrophage activating and deactivating cytokines have been characterized in mammalian systems but little is known about these immunoregulatory molecules in fish. Using gel permeation and chromatofocusing fast performance liquid chromatography (GP-FPLC and C-FPLC) we partially purified a macrophage deactivating factor (MDF) from mitogen-induced goldfish kidney leukocytes. Inhibition of the macrophage-derived nitric oxide (NO) response induced by this MDF was time-, dose- and temperature-dependent. Macrophages pre-treated for 6 or 24 h with MDF before activation with macrophage activating factors (MAF) and/or bacterial lipopolysaccharide (LPS) exhibited a down-regulation in their NO response, while those treated with MDF 24 h after activation with MAF and LPS did not. MDF treatment also impaired the NO response of goldfish macrophages infected with the mammalian protozoan parasite Leishmania major. These results suggest that MDF exhibits its inhibitory effect downstream of the converging intracellular pathways induced by LPS and/or L. major. The novel teleost MDF has an approximate Mr of 15 kD and a pI < 4, and is the first endogenous molecule of teleosts known to down regulate macrophage antimicrobial responses.

Lipopolysaccharide Induces in Macrophages the Synthesis of the Suppressor of Cytokine Signaling 3 and Suppresses Signal Transduction in Response to the Activating Factor IFN-γ

The goal of this study was to investigate how bacterial LPS affects macrophage responsiveness to the activating factor IFN-γ. Pretreatment of macrophages with LPS for &lt;2 h increased the transcriptional response to IFN-γ. In contrast, simultaneous stimulation with IFN-γ and LPS, or pretreatment with LPS for &gt;4 h, suppressed Stat1 tyrosine 701 phosphorylation, dimerization, and transcriptional activity in response to IFN-γ. Consistently, the induction of MHCII protein by IFN-γ was antagonized by LPS pretreatment. Neutralizing Abs to IL-10 were without effect on LPS-mediated suppression of Stat1 activation. Decreased IFN-γ signal transduction after LPS treatment corresponded to a direct induction of suppressor of cytokine signaling3 (SOCS3) mRNA and protein. Under the same conditions socs1, socs2, and cis genes were not transcribed. In transfection assays, SOCS3 was found to suppress the transcriptional response of macrophages to IFN-γ. A causal link of decreased IFN-γ signaling to SOCS3 induction was also suggested by the LPS-dependent reduction of IFN-γ-mediated Janus kinase 1 (JAK1) activation. Further consistent with inhibitory activity of SOCS3, LPS also inhibited the JAK2-dependent activation of Stat5 by GM-CSF. Our results thus link the deactivating effect of chronic LPS exposure on macrophages with its ability to induce SOCS3.

Stat1 combines signals derived from IFN-gamma and LPS receptors during macrophage activation

Complete activation of macrophages during immune responses results from stimulation with the activating cytokine interferon-gamma (IFN-gamma) and a second stimulus, usually a microbial product. Bacterial infection of macrophages, or treatment with bacterial lipopolysaccharide (LPS), resulted in rapid Stat1 phosphorylation on Ser727 (S727) independently of concomitant tyrosine phosphorylation. IFN-gamma also caused rapid phosphorylation of S727. In both situations, S727 phosphorylation was reduced by pre-treatment of cells with the serine kinase inhibitor H7. When macrophages were treated sequentially or simultaneously with LPS and IFN-gamma, the pool of molecules phosphorylated on both Tyr701 (Y701) and S727 was strongly increased. Consistently, Stat1-dependent transcription in response to IFN-gamma was significantly enhanced if the cells were pre-treated with bacterial LPS. The relative amount of S727-phosphorylated Stat1 in the non-tyrosine phosphorylated fraction was considerably smaller than that in the tyrosine-phosphorylated fraction. No evidence was found for an effect of S727 phosphorylation on the phosphorylation of Y701 by IFN-gamma. Thus, serine and tyrosine phosphorylation of Stat1 are caused independently of each other, but the serine kinase may recognize tyrosine-phosphorylated Stat1 preferentially in the course of an IFN-gamma response. The data suggest Stat1 to be a convergence point for immunological stimuli in a macrophage proinflammatory response.

Control of Leishmania major Infection in Mice Lacking TNF Receptors

TNF participates in the induction of nitric oxide (NO) production and macrophage activation, leading to the elimination of intracellular pathogens. We previously found that TNF receptor p55-deficient mice (TNFRp55−/−) control replication of Leishmania major in vivo but fail to resolve their lesions. Here we report that mice lacking the p75 receptor (TNFRp75−/−) or both receptors (TNFRp55p75−/−), also control parasite replication, albeit mice lacking the p55 receptor (either TNFRp55−/− or TNFRp55p75−/−) are delayed in their elimination of L. major compared with controls. All TNF receptor-deficient mice developed a Th1-type immune response and up-regulated inducible NO synthase (iNOS) mRNA gene expression in lesions during infection. Thus, neither TNF receptor appears to be absolutely required for NO production or elimination of L. major in vivo. In vitro, however, while macrophages from naive TNFRp75−/− mice could be activated to produce NO and kill L. major, we observed a defect in NO production and parasite killing by resident peritoneal macrophages from naive TNFRp55−/− or TNFRp55p75−/− mice. However, when macrophages were elicited with leishmanial Ag from 4-wk-infected TNFRp55−/−or TNFRp55p75−/− mice, they produced NO and were leishmanicidal. These data suggest that the TNFRp75 plays no essential role in L. major infection in mice and that the p55 receptor may be required for optimal macrophage activation. However, the results also show that a mechanism exists by which macrophages can be primed in vivo during L. major infection to produce NO and kill L. major in the absence of signaling through either of the TNF receptors.

Essential Roles for Granulocyte-Macrophage Colony-Stimulating Factor (GM-CSF) and G-CSF in the Sustained Hematopoietic Response ofListeria monocytogenes–Infected Mice

The in vivo roles of granulocyte-macrophage colony-stimulating factor (GM-CSF) and granulocyte (G)-CSF were studied in factor-deficient gene-targeted knockout mice infected with the facultative intracellular bacterium Listeria monocytogenes.Previous results showed that G-CSF−/− mice had an underlying selective deficiency in granulopoiesis, but GM-CSF−/− mice had little disturbance in resting hematopoiesis. Nevertheless, in this study it is revealed that 3 days after intraperitoneal infection with 2 × 105Listeria, GM-CSF−/− mice harbored 50-fold more organisms in their spleen and liver than similarly infected wild-type mice. This was accompanied by a severe depletion of bone marrow hematopoietic cells and a deficient inflammatory response in their peritoneal cavity. Thus, GM-CSF is essential for emergency, but not resting, hematopoiesis. In contrast, G-CSF−/− mice were markedly susceptible to low doses (2 × 104) ofListeria intraperitoneally. After infection, the acute (1 day) granulocyte infiltration to the peritoneal cavity was normal compared with wild type, but the more prolonged monocyte response was deficient, reflecting a continued decrease in bone marrow cellularity and hematopoiesis over 3 days, which was not observed in infected wild-type mice. It is thus apparent that G-CSF deficiency affects monocytopoiesis as well as granulopoiesis during infection.

Essential Roles for Granulocyte-Macrophage Colony-Stimulating Factor (GM-CSF) and G-CSF in the Sustained Hematopoietic Response ofListeria monocytogenes–Infected Mice

The in vivo roles of granulocyte-macrophage colony-stimulating factor (GM-CSF) and granulocyte (G)-CSF were studied in factor-deficient gene-targeted knockout mice infected with the facultative intracellular bacterium Listeria monocytogenes.Previous results showed that G-CSF−/− mice had an underlying selective deficiency in granulopoiesis, but GM-CSF−/− mice had little disturbance in resting hematopoiesis. Nevertheless, in this study it is revealed that 3 days after intraperitoneal infection with 2 × 105Listeria, GM-CSF−/− mice harbored 50-fold more organisms in their spleen and liver than similarly infected wild-type mice. This was accompanied by a severe depletion of bone marrow hematopoietic cells and a deficient inflammatory response in their peritoneal cavity. Thus, GM-CSF is essential for emergency, but not resting, hematopoiesis. In contrast, G-CSF−/− mice were markedly susceptible to low doses (2 × 104) ofListeria intraperitoneally. After infection, the acute (1 day) granulocyte infiltration to the peritoneal cavity was normal compared with wild type, but the more prolonged monocyte response was deficient, reflecting a continued decrease in bone marrow cellularity and hematopoiesis over 3 days, which was not observed in infected wild-type mice. It is thus apparent that G-CSF deficiency affects monocytopoiesis as well as granulopoiesis during infection.

Intranasal infection of beige mice with Mycobacterium avium complex: role of neutrophils and natural killer cells

Beige mice show increased susceptibility to intranasal infection with organisms of the Mycobacterium avium complex (MAC) compared with their immunocompetent congenics, C57BL/6 mice. This increased susceptibility was clear 2 weeks postinfection, before the activation of the specific immune response. T lymphocytes from 4-week infected beige mice, cultured in vitro, produced amounts of gamma interferon similar to those found in cells from C57BL/6 mice. Macrophage activation, as judged by NO production and lysis of the macrophage target P815, occurred in the lungs of beige mice. Despite the inability of bone marrow-derived NK cells from beige mice to lyse NK-susceptible YAC-1 cells, their gamma interferon production was normal. Monoclonal antibody to NK1.1 was used to deplete C57BL/10 mice of lytic activity against YAC-1 cells without exacerbating infection between 2 and 6 weeks of observation, making it unlikely that any deficiency in NK cells was the cause of susceptibility in beige mice. There was a striking influx of neutrophils in the lungs of beige mice compared with C57BL/6. More than half of the MAC organisms appeared associated with the neutrophils of beige mice, while in C57BL/6 mice, most MAC organisms were associated with cells of macrophage/monocyte morphology. Injection of monoclonal antibody specific for neutrophils failed to eliminate those cells from the lungs of beige mice. However, in C57BL/6 mice, neutrophil numbers were reduced by 95% without exacerbating the infection. We conclude that, although neutrophils are not essential to the relative resistance of C57BL/6 mice, the known deficiencies in both neutrophils and macrophages account for the susceptibility of beige mice.

Macrophage activating factor(s) secreted by mitogen stimulated goldfish kidney leukocytes synergize with bacterial lipopolysaccharide to induce nitric oxide production in teleost macrophages

Recent studies in our laboratory demonstrated that fish macrophages produce nitric oxide. To elucidate the mechanisms which regulate nitric oxide production in teleosts, we examined whether macrophage activating factors (MAFs) secreted by mitogen stimulated leukocytes, induced nitric oxide production in a long-term cultured macrophage cell line and in primary cultures of kidney macrophages from the goldfish. The results indicate that both primary and long term cultured goldfish macrophages produce nitric oxide in response to MAF or bacterial lipopolysaccharide (LPS), and co-stimulation with both factors results in a synergistic induction of nitric oxide production. MAF that induced nitric oxide production were present in leukocyte supernatants as early as 24 h after addition of mitogens to cell cultures. The production of MAF was dependent upon the incubation temperature, presence of serum in the culture medium and duration of incubation: maximal MAF activity was detected in 72-96 h supernatants raised in media with serum at 30 degrees C. MAF-induced nitric oxide production by long term cultured macrophages was inhibited by 1000 microM NG-monomethyl-L-arginine or amino-guanidine, indicating an L-arginine-dependent metabolic pathway for the production of the reactive nitrogen intermediates in teleosts. The biochemical events of cytokine induced nitric oxide production by teleost macrophages appear to be similar to those of mammalian macrophages.

Effects of immunosuppressive therapy on expression of inducible nitric oxide synthase (iNOS) during cardiac allograft rejection

Recent studies have indicated a role for nitric oxide (NO) in alloimmune responses and in allograft rejection. iNOS mRNA, protein and enzyme activity are induced in myocardium during cardiac allograft rejection. NO produced by iNOS is negatively inotropic and has the potential to be cytotoxic to cardiac myocytes. To investigate whether immunosuppressive agents would alter the expression of iNOS during cardiac allograft rejection, hearts from Wistar-Furth rats were transplanted into the abdomen of Lewis recipients. At day 5 allografts from treated and untreated animals were removed for pathological and biochemical examination. At day 5 the untreated allografts exhibited histological evidence of marked rejection (edema, infiltration with macrophages and lymphocytes, necrosis of cardiac muscle fibers). Abundant iNOS mRNA was apparent in Northern blots and iNOS enzyme activity was increased in ventricular homogenates and in cardiac myocytes purified from the untreated rejecting allografts. Incubation of isolated purified cardiac myocytes from normal rats for 24 h with cytokines known to be present during allograft rejection (IL-1 beta, TNF-alpha and IFN-gamma) was also associated with increased iNOS mRNA and enzyme activity. When Wistar-Furth to Lewis allografts were treated from time of transplantation with FK 506, cyclosporine A, dexamethasone or a combination of all three drugs, histological evidence of rejection and the levels of iNOS mRNA and enzyme activity in ventricular homogenates were reduced significantly below those observed in the untreated allografts. The data in a rat model indicate that immunosuppressive drugs reduce myocardial iNOS mRNA and enzyme activity in rejecting cardiac allografts. The results are consistent with the hypothesis that the alloimmune response and cytokine release are involved in the expression of iNOS during cardiac transplantation rejection.

Bacterial stimulators of macrophages

Our current understanding of the interaction between bacteria and macrophages, cells of the immune system that play a major role in the defense against infection, is summarized. Cell-surface structures of Gram-negative and Gram-positive bacteria that account for these interactions are described in detail. Besides surface structures, soluble bacterial molecules, toxins that are derived from pathogenic bacteria, are also shown to modulate macrophage functions. In order to affect macrophage functions, bacterial surface structures have to be recognized by the macrophage and toxins have to be taken up. Subsequently, signal transduction mechanisms are initiated that enable the macrophage to respond to the invading bacteria. To destroy bacteria, macrophages employ many strategies, among which antigen processing and presentation to T cells, phagocytosis, chemotaxis, and different bactericidal mechanisms are considered to be the main weapons.

Chicken interferon-mediated induction of major histocompatibility complex class II antigens on peripheral blood monocytes

Conditioned medium containing immune interferon (IFN) activity was prepared by stimulating spleen lymphocytes obtained from inbred SC chickens with 10 micrograms concanavalin A (Con A) for 48 h. Pretreatment of spleen cells with monoclonal antibody against CD4, but not CD8, abrogated IFN production suggesting that CD4+ lymphocytes are responsible for immune IFN production. Immune IFN was purified 25-fold from Con A conditioned medium using controlled-pore glass column chromatography resulting in an increase in specific antiviral activity from 7 to 3290 units mg-1. Partially purified immune IFN retained antiviral and macrophage-activating factor (MAF)-like activities. Normal peripheral blood macrophages, when cultured in the presence of partially purified immune IFN, showed a dose-dependent increase in cell surface major histocompatibility complex Class II antigen expression by flow cytometry. Northern blot analysis of mRNA obtained from IFN-treated macrophages showed a concomitant increase in Class II gene expression. This effect was more obvious in cells induced for 48 h than in those induced for 24 h. These results strongly suggest that existence of an avian homologue of the MAF-like activity.

Presentation of exogenous antigens by macrophages: analysis of major histocompatibility complex class I and II presentation and regulation by cytokines

There is an antigen presenting cell (APC) in the lymphoid organs capable of presenting exogenous antigen (Ag) with major histocompatibility complex (MHC) class I molecules. This study was initiated to isolate clones of these APC to definitively establish their phenotype and to further study their properties. Murine bone marrow macrophages (BM M psi) were immortalized by overexpression myc and raf oncogenes. Five BM M psi cell lines were generated that are phagocytic and expressed at their surface M psi differentiation Ag. All five cell lines processed and presented exogenous ovalbumin (OVA) with MHC class I molecules. They all presented OVA-linked to a phagocytic substrate 10(2)-10(4)-fold more efficiently than soluble Ag. Clonal isolates of two of the M psi cell lines had an identical phenotype and functional properties as the uncloned lines. These results definitively establish that M psi are APC with the capacity of presenting exogenous Ag with MHC class I molecules. Interferon (IFN)-gamma interleukin-4, granulocyte-macrophage colony stimulating factor and lipopolysaccharide either alone or in combination induced little or no augmentation and in some cases decreased presentation of exogenous OVA with MHC class I. In contrast, all of M psi activating factors increased MHC class I expression. Moreover, IFN-gamma increased the presentation of cytosolic OVA, demonstrating differences between the presentation of cytosolic Ag versus exogenous Ag with MHC class I. Finally, some lines constitutively processed and presented exogenous OVA with MHC class II while others only presented after stimulation with IFN-gamma. These results demonstrate that the pathways involved in the presentation of exogenous Ag with MHC class I and class II are independently regulated and that a cloned cell is capable of presenting exogenous Ag through both pathways.

Production of inflammatory mediators by human macrophages obtained from ascites

Ascites is a readily available source of human macrophages (M phi), which can be used to study M phi functions in vitro. We characterized the mediators of inflammation produced by human peritoneal M phi (hp-M phi) obtained from patients with portal hypertension and ascites. The production of the cytokines interleukin-1 beta (IL-1 beta), interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-alpha) was found to be lipopolysaccharide (LPS) concentration dependent (0-10 micrograms/ml) with a maximal production at 10 micrograms/ml and also dependent on the time of exposure to the stimulus (0-36 h). IL-1 beta, IL-6 and TNF-alpha production after LPS administration reached a plateau at 24 h. In vitro stimulation for 24 h with LPS does not influence the eicosanoid production from endogenous arachidonate. 13 min of exposure of the cells to the calcium ionophore A23187 gives a significant increase in eicosanoid production from both exogenous and endogenous arachidonate. The main eicosanoids produced are the 5-lipoxgenase products LTB4 and 5-hydroxyeicosatetraenoic acid (HETE). The increase in production of the other eicosanoids is not significant. The eicosanoid production depends on the stimulus concentration. The optimal A23187 concentration is 1 microM. Oxygen radical production was measured in the M phi by a flowcytometric method. The fluorescence intensity of phorbol 12-myristate 13-acetate stimulated and dihydro-rhodamine 123 loaded hp-M phi increases significantly after 15 min. We conclude that LPS stimulation of hp-M phi from liver disease results in similar production of IL-1 beta, IL-6 and TNF-alpha, but that the profile of the eicosanoid production of these M phi stimulated with LPS and A23187 differs from M phi of other origin and species.

Role of Acetylsalicylic Acid in Cytokine Stimulation of Macrophages in Antibody-Dependent Cellular Cytotoxicity (ADCC)

In addition to the spectrum of biological action already known to be exhibited by acetylsalicylic acid (ASA) as an analgesic, anti-inflammatory and platelet aggregation inhibitor, there is growing evidence of a stimulatory effect on the immune system. ASA has been found to increase the production ofcytokines and to increase the activity of various leukocytes. The action of ASA on the activity of mouse peritoneal macrophages was therefore investigated in the present study. Therapeutically effective concentrations of ASA, which are known to decrease levels of prostaglandins, had neither a stimulating nor an inhibiting influence on antibody-dependent cellular cytotoxicity (ADCC) or on the binding capacity of macrophages with regard to SW 948 tumour cells. Likewise ASA had little or no adverse effect on the capacity of the macrophages for stimulation by interferon-gamma (IFN-gamma) and interleukin-4 (IL-4). Taken together, the immunostimulant effect of ASA shown in the literature as an increased production of interleukin-2 (IL-2) and IFN, could not be confirmed on the basis of the macrophage cytotoxiclty.

Effector functions of activated macrophages against parasites

Evidence in experimental animals indicates a major role for cytokine-activated macrophages as effector cells in protective immunity against parasites. Research on cytokine function during this past year has contributed many insights into the immune mechanisms regulating murine macrophage function as well as the effector molecules employed by these cells to kill both intracellular and extracellular parasites.

T-cell and cytokine responses in leishmaniasis

Intracellular pathogens, particularly those that inhabit lymphocytes and macrophages, represent unique challenges to the immune system. Leishmania are protozoan parasites that replicate exclusively in macrophages and are thus in an excellent position to influence lymphocyte responses. T cell responses are critical in determining the outcome of infections with Leishmania. In both murine and human infections, strong T helper type 2 responses have been associated with disease, and a decreased or absent T helper type 2 response has been associated with healing.

Immune responses associated with susceptibility of C57BL/10 mice to Leishmania amazonensis

Leishmaniae are protozoans which, depending upon both the host and parasite species, can cause either a healing or nonhealing infection. While C57BL/10 mice are able to heal following infection with Leishmania major, they fail to heal following infection with Leishmania amazonensis. In order to address the role of Th1 and Th2 cell responses in the outcome of these infections in C57BL/10 mice, gamma interferon (IFN-gamma) and interleukin-4 (IL-4) production was assessed. While cells from L. major-infected C57BL/10 mice produced high levels of IFN-gamma, cells from L. amazonensis-infected animals produced little or no IFN-gamma. On the other hand, IL-4 was produced only by cells from L. amazonensis-infected C57BL/10 mice, but this production was restricted to the first few weeks of infection. Later in infection, when lesions were evident, no IL-4 was detected. Treatment of BALB/c mice with a monoclonal antibody (11B11) directed against IL-4 induced a dramatic reduction in L. amazonensis lesions. This reduction was associated with a decrease in IL-4 levels and an increase in IFN-gamma production. However, only a slight reduction in lesion sizes and parasite numbers was observed when anti-IL-4-treated C57BL/10 mice were infected with L. amazonensis. These results suggest that IL-4 may have an important role in mediating susceptibility to L. amazonensis in BALB/c mice, as previously demonstrated for L. major. More importantly, however, the data suggest that susceptibility to L. amazonensis in C57BL/10 mice is due to the absence of a Th1 cell response, rather than to the presence of a Th2 cell response.

Tyrosine phosphorylation is an early and requisite signal induced by interferon-gamma in HL-60 cells

Interferon-gamma (IFN gamma) is a potent immunomodulatory cytokine. However, the early mechanisms which mediate the pleiotropic effects of IFN gamma on different cells are as yet poorly understood. Therefore, we tested the role of tyrosine phosphorylation in signalling induced by IFN gamma. IFN gamma was found to induce rapid tyrosine phosphorylation of several proteins in HL-60 cells. This effect was detectable by 2 min, reached a maximum by about 4-16 min and thereafter declined. Tyrosine phosphorylation was dependent on receptor occupation and was maximally stimulated by 10 ng/ml IFN gamma. Treatment of HL-60 cells with the tyrosine kinase inhibitors, genistein and herbimycin A, inhibited both IFN gamma-stimulated tyrosine phosphorylation and IFN gamma-induced Fc receptor expression. Thus, increased tyrosine phosphorylation appears to be an obligatory early and proximal signal mediating at least some of the later cellular responses induced by IFN gamma in HL-60 cells.

Nitric oxide-mediated neuronal injury in multiple sclerosis

Although several explanations have been proposed for destruction of myelin and oligodendrocytes in multiple sclerosis, there is no proven mechanism of injury. We postulate that the autoimmune response seen in multiple sclerosis results in a cytokine-mediated increase in nitric oxide production by macrophages/microglia, smooth muscle cells and/or endothelium of the central nervous system. 3 mechanisms of cellular damage due to nitric oxide are proposed: 1. direct nitric oxide cytotoxicity; 2. injury due to peroxynitrite formation from superoxide anion and nitric oxide; and 3. nitric oxide-mediated elevations of cellular cGMP that enhance tumor necrosis factor-alpha toxicity. In support of these hypotheses, the anti-inflammatory effectors, dexamethasone and transforming growth factor-beta, ameliorate symptoms seen in clinical multiple sclerosis and experimental allergic encephalitis, respectively. These 2 immunomodulators also inhibit induction of cytokine-mediated nitric oxide production by macrophages. An experimental design and therapeutic interventions which will evaluate the role of nitric oxide in the pathophysiology of experimental allergic encephalitis are presented.

Functional characterization of a hybrid human-mouse interferon gamma receptor: evidence for species-specific interaction of the extracellular receptor domain with a putative signal transducer

The human interferon gamma (IFN-gamma) receptor expressed in mouse cells displays binding properties indistinguishable from those of the resident receptor on human cells. Still, mouse cells expressing the human IFN-gamma receptor remain insensitive to human IFN-gamma. It is widely accepted that at least one species-specific cofactor encoded within human chromosome 21 is required for signal transduction. To define structural domains of the human IFN-gamma receptor responsible for this species-specific interaction, a hybrid between the human and the murine receptor was constructed and expressed in mouse L929 cells or in mouse L cell-derived SCC16-5 cells, which contain human chromosome 21. This hybrid receptor, which consisted of the extracellular domain of the human IFN-gamma receptor and the transmembrane and cytoplasmic domains of the murine IFN-gamma receptor, was found to bind human IFN-gamma with high affinity. However, only SCC16-5 cells expressing the human/mouse hybrid receptor were responsive to human IFN-gamma as revealed by enhanced expression of major histocompatibility complex class I antigens, induction of the transcription factor IRF-1, and induction of a partial antiviral state. These findings strongly suggest that IFN-gamma-mediated signal transduction requires a species-specific interaction of the extracellular portion of the known ligand-binding IFN-gamma receptor chain with an additional, presumably membrane-anchored receptor subunit.