Impaired neutrophil response and CD4+ T helper cell 1 development in interleukin 6-deficient mice infected with Candida albicans

Clinical review: a paradigm shift: the bidirectional effect of inflammation on bacterial growth. Clinical implications for patients with acute respiratory distress syndrome

Clinical studies have shown positive associations among sustained and intense inflammatory responses and the incidence of bacterial infections. We hypothesized that cytokines secreted by the host during acute respiratory distress syndrome may indeed favor the growth of bacteria and explain the association between exaggerated and protracted systemic inflammation and the frequent development of nosocomial infections. To test this hypothesis, we conducted in vitro studies evaluating the extracellular and intracellular growth response of three clinically relevant bacteria in response to graded concentrations of pro-inflammatory cytokines tumor necrosis factor-alpha, IL-1beta, and IL-6. In these studies, we identified a U-shaped response of bacterial growth to pro-inflammatory cytokines. When the bacteria were exposed in vitro to a lower concentration of cytokines, extracellular and intracellular bacterial growth was not promoted and human monocytic cells were efficient in killing the ingested bacteria. Conversely, when bacteria were exposed to higher concentrations of pro-inflammatory cytokines, intracellular and extracellular bacterial growth was enhanced in a dose-dependent manner. The bidirectional effects of proinflammatory cytokines on bacterial growth may help to explain the frequent occurrence of nosocomial infections in patients with unresolving acute respiratory distress syndrome.

The role of IL-1beta in the regulation of IL-8 and IL-6 in human corneal epithelial cells during Pseudomonas aeruginosa colonization

PURPOSE

Recent studies have shown that the levels of interleukin (IL)-1beta, IL-6 and IL-8 are associated with the severity of infectious diseases. The purpose of this study was to investigate whether IL-1beta regulates the expression of IL-6 and IL-8 in human corneal epithelial cells during Pseudomonas aeruginosa colonization.

METHODS

Confluent immortalized human corneal epithelial cells were challenged with P. aeruginosa 6294 in the presence of anti-human IL-1beta antibody or matched control antibody. The cells were also challenged with recombinant IL-1beta protein without bacterial colonization. Expression of IL-1beta, IL-6 and IL-8 mRNA and protein was detected by reverse transcription (RT)-PCR and by enzyme-linked immunosorbent assay (ELISA), respectively. IL-1beta localization was determined by immunohistochemistry.

RESULTS

Human corneal epithelial cells expressed low levels of IL-1beta and high levels of IL-6 and IL-8 during P. aeruginosa colonization. Addition of IL-1beta Ab resulted in a significant decrease (P < 0.05) in IL-8 protein expression at 4 h, 8 h and 12 h. Addition of IL-1beta Ab reduced IL-6 protein expression at 8 h and increased IL-6 protein expression at 12 h. Addition of recombinant IL-1beta protein alone strongly stimulated the expression of IL-8 and IL-6. Immunohistochemical staining showed that IL-1beta protein was present both intracellularly and extracellularly in P. aeruginosa colonized cells.

CONCLUSIONS

IL-1beta is able to modulate expression of both IL-6 and IL-8 at transcriptional and post-transcriptional levels in human corneal epithelial cells.

Candida albicans is phagocytosed, killed, and processed for antigen presentation by human dendritic cells

Candida albicans is a component of the normal flora of the alimentary tract and also is found on the mucocutaneous membranes of the healthy host. Candida is the leading cause of invasive fungal disease in premature infants, diabetics, and surgical patients, and of oropharyngeal disease in AIDS patients. As the induction of cell-mediated immunity to Candida is of critical importance in host defense, we sought to determine whether human dendritic cells (DC) could phagocytose and degrade Candida and subsequently present Candida antigens to T cells. Immature DC obtained by culture of human monocytes in the presence of granulocyte-macrophage colony-stimulating factor and interleukin-4 phagocytosed unopsonized Candida in a time-dependent manner, and phagocytosis was not enhanced by opsonization of Candida in serum. Like macrophages (Mphi), DC recognized Candida by the mannose-fucose receptor. Upon ingestion, DC killed Candida as efficiently as human Mphi, and fungicidal activity was not enhanced by the presence of fresh serum. Although phagocytosis of Candida by DC stimulated the production of superoxide anion, inhibitors of the respiratory burst (or NO production) did not inhibit killing of Candida, even when phagocytosis was blocked by preincubation of DC with cytochalasin D. Further, although apparently only modest phagolysosomal fusion occurred upon DC phagocytosis of Candida, killing of Candida under anaerobic conditions was almost equivalent to killing under aerobic conditions. Finally, DC stimulated Candida-specific lymphocyte proliferation in a concentration-dependent manner after phagocytosis of both viable and heat-killed Candida cells. These data suggest that, in vivo, such interactions between DC and C. albicans may facilitate the induction of cell-mediated immunity.

The IL-6-soluble IL-6Ralpha autocrine loop of endothelial activation as an intermediate between acute and chronic inflammation: an experimental model involving thrombin

Thrombin is a procoagulant and proinflammatory molecule in vivo. In vitro, thrombin has been shown to induce endothelial activation, notably IL-8 secretion and adhesion molecule expression. In this study, we showed that thrombin may induce a new cascade leading from acute to chronic inflammation. Thrombin was able to induce the production of both IL-6 and monocyte chemotactic protein-1 (MCP-1) by HUVEC independently of IL-1alphabeta and TNF-alpha. Addition of physiological concentrations of exogenous soluble IL-6Ralpha (sIL-6Ralpha) to thrombin-activated HUVEC was sufficient to increase the amounts of MCP-1 produced, but not those of IL-8. These effects could be blocked by anti-IL-6 or anti-sIL-6Ralpha blocking mAb, demonstrating the existence of an autocrine loop of MCP-1 secretion, involving the IL-6/IL-6Ralpha/gp130 complex on HUVEC. In addition, we identified IL-8-activated neutrophils as a potential source of sIL-6Ralpha because IL-8 induced IL-6Ralpha shedding from the neutrophil membranes and increased in parallel sIL-6Ralpha concentrations in neutrophil supernatants. Furthermore, addition of neutrophils to thrombin-activated HUVEC significantly increased MCP-1 secretion, which could be decreased by blocking IL-6. Thus, thrombin-activated endothelium may induce a cascade of events characterized by IL-8 secretion, neutrophil local infiltration, and the release of IL-6Ralpha from neutrophil membranes. sIL-6Ralpha may then complex with IL-6 and increase the amount of MCP-1 produced by thrombin-activated endothelium, favoring monocyte infiltration, and the transformation of acute into chronic inflammation.

Overexpression of interleukin-6 aggravates viral myocarditis: impaired increase in tumor necrosis factor-alpha

The process of inflammation and immune response is regulated by proinflammatory cytokines. Interleukin-6 (IL-6), one of the proinflammatory cytokines, plays a potentially critical role in viral-induced myocarditis. Our previous work demonstrates that exogenous IL-6 administration, given at the time of encephalomyocarditis virus (EMCV) inoculation in C3H/HeJ mice, has a protective effect on myocardium and improves survival rates. In the present study, we examined whether overexpression of IL-6 modified viral myocarditis. On day 3 and 10 after inoculation with EMCV, the ratio of heart weight to body weight and myocardial injury were significantly increased in IL-6 transgenic mice (IL-6TG). On day 3, a reduction of viral clearance was shown by the presence of elevated viral titers and viral replication in the heart of IL-6TG. The concentrations of serum tumor necrosis factor- alpha (TNF alpha) were dramatically increased in wild-type mice on day 1, in contrast, this change was not observed in IL-6TG. Treatment with recombinant human TNF (2 microg) significantly improved viral clearance in the IL-6TG hearts. Thus, overexpression of IL-6 promotes myocardial injury by interrupting both the cytokine network and viral clearance. These experiments suggest the possibility that IL-6 is one of the factors that accelerates tissue damage, including myocardial injury, in the viral myocarditis.

IL-1 enhances T cell-dependent antibody production through induction of CD40 ligand and OX40 on T cells

IL-1 is a proinflammatory cytokine that plays pleiotropic roles in host defense mechanisms. We investigated the role of IL-1 in the humoral immune response using gene-targeted mice. Ab production against SRBC was significantly reduced in IL-1alpha/beta-deficient (IL-1(-/-)) mice and enhanced in IL-1R antagonist(-/-) mice. The intrinsic functions of T, B, and APCs were normal in IL-1(-/-) mice. However, we showed that IL-1(-/-) APCs did not fully activate DO11.10 T cells, while IL-1R antagonist (-/-) APCs enhanced the reaction, indicating that IL-1 promotes T cell priming through T-APC interaction. The function of IL-1 was CD28-CD80/CD86 independent. We found that CD40 ligand and OX40 expression on T cells was affected by the mutation, and the reduced Ag-specific B cell response in IL-1(-/-) mice was recovered by the treatment with agonistic anti-CD40 mAb both in vitro and in vivo. These observations indicate that IL-1 enhances T cell-dependent Ab production by augmenting CD40 ligand and OX40 expression on T cells.

Effect of interleukin-6 deficiency on the formation of periapical lesions after pulp exposure in mice

OBJECTIVE

The multifunctional cytokine interleukin-6 (IL-6) has actions on multiple cell types, including promotion of the development of immune cells and osteoclasts. Periapical inflammation as the result of root canal infection is characterized by the accumulation of inflammatory cells and bone resorption. The effect of IL-6 on periapical lesion formation after pulpal infection is unknown. We sought to determine whether deletion of IL-6 affects periapical lesion formation after pulp exposure.

METHODS

Molar pulps of homozygous IL-6 knock-out mice (IL-6(-/-), strain B6, 129-Il6tm1Koe ) and wild-type mice (IL-6(+/+)) were exposed, and the mice were killed at 1, 2, 3, 5, and 8 weeks after the exposure. Mouse jaws were decalcified and prepared for histologic examination of periapical lesions.

RESULTS

The IL-6(-/-) mice developed larger periapical lesions more rapidly than did the IL-6(+/+) mice.

CONCLUSIONS

IL-6 deletion promoted periapical lesion development.

In vivo neutralization of human IL-6 (hIL-6) achieved by immunization of hIL-6-transgenic mice with a hIL-6 receptor antagonist

Neutralization of IL-6 represents an attractive therapeutic option in several diseases, including B cell neoplasia, osteoporosis, and autoimmunity. Therapeutic attempts in humans have shown that administration of injectable doses of a mAb to IL-6 does not provide efficient neutralization of the cytokine in vivo. Therefore, alternative approaches are needed. In this study, we evaluated whether the Ab response to human IL-6 (hIL-6) elicited by vaccination with Sant1 (a hIL-6 variant with seven amino acid substitutions) was able to fully correct in vivo the clinical and biological effects of a chronic endogenous overproduction of hIL-6 in the hIL-6-transgenic NSE/hIL-6 mice. Because of the overexpression of hIL-6, occurring since birth, with circulating levels in the nanogram per milliliter range, NSE/hIL-6 mice have a marked decrease in growth rate, associated with decrease in insulin-like growth factor I levels, and represent an animal model of the growth impairment associated with human chronic inflammatory diseases. Following immunization with Sant1, but not with hIL-6, NSE/hIL-6 mice developed high titers of polyclonal Abs to hIL-6. The Abs, acquired by transplacental transfer, effectively neutralized IL-6 activities in vivo as shown by the complete correction of the growth defect and normalization of insulin-like growth factor levels in the hIL-6-transgenic offspring. Immunization with Sant1 could therefore represent a novel and simple therapeutic approach for the specific neutralization of IL-6 in humans.

Humanized antibody to human interleukin-6 receptor inhibits the development of collagen arthritis in cynomolgus monkeys

In the present study, we demonstrated the anti-arthritic effect of humanized anti-human IL-6 receptor (IL-6R) antibody, MRA, in cynomolgus monkey. MRA can react with monkey IL-6R and block signal transduction of IL-6. Collagen-induced arthritis (CIA) was induced by twice immunizing with bovine type II collagen (CII) emulsified with complete adjuvant. MRA was intravenously injected once a week, from the day of the first collagen immunization, for 13 weeks. The symptoms of arthritis were evaluated using a visual scoring system and radiography. Inflammatory parameters (C-reactive protein (CRP), fibrinogen, and erythrocyte sedimentation rate (ESR) and concentrations of anti-CII antibody, anti-MRA antibody, and MRA were monitored regularly. At the end of the study, histological evaluation was carried out. MRA, at a dose of 10 mg/kg, gave rise to statistically significant suppression. The elevation of serum CRP and fibrinogen levels and ESR were also inhibited. Furthermore, radiographic and histological examination showed that MRA treatment suppressed joint destruction. Our results demonstrate that IL-6 plays an important role in monkey CIA and that MRA may be an attractive agent for the treatment of rheumatoid arthritis.

Interaction of Bordetella pertussis with mast cells, modulation of cytokine secretion by pertussis toxin

Together with macrophages and dendritic cells, mast cells have recently been shown to interact with certain pathogenic bacteria and present microbial antigens to the immune system. We show here that Bordetella pertussis can adhere to and be phagocytosed by mast cells. In addition, mast cells are able to process and present B. pertussis antigens to T lymphocytes. Furthermore, exposure of mast cells to B. pertussis induced the release of the proinflammatory cytokines tumour necrosis factor alpha (TNF-alpha) and interleukin 6 (IL-6). The release of IL-6 was strongly reduced by pertussis toxin expressed by B. pertussis. The production of IL-10, but not that of IL-4, by mast cells was also inhibited by pertussis toxin. Depletion of mast cells in vivo resulted in significant reduction of early TNF-alpha production in bronchoalveolar lavage (BAL) fluids of B. pertussis-infected mice. These data suggest that mast cells may play a role in the induction of immune responses against B. pertussis through the release of cytokines, especially TNF-alpha.

Enhancement of T helper2 response in the absence of interleukin (IL-)6; an inhibition of IL-4-mediated T helper2 cell differentiation by IL-6

Functional roles of interleukin (IL-)6 in T cell response were investigated. Mice deficient in IL-6 and wild mice were immunized with antigens (myelin oligodendrocyte glycoprotein or methylated BSA) and production of IL-4 and interferon (IFN)-gamma by regional lymph nodes was measured. IL-6 deficiency led to an enhancement of IL-4 and an inhibition of IFN-gamma production. Moreover, polyclonal stimulation of spleen T cells from unimmunized IL-6-deficient mice with anti-CD3 plus anti-CD28 antibodies (Abs) demonstrated an enhancement of T helper (Th)(2)responses. The presence of IL-6, however, augmented IL-4 production but it inhibited IFN-gamma expression by spleen T cells in response to polyclonal stimulation and by antigen-primed spleen T cells in response to re-challenge with the antigen. In contrast, the induction of spleen CD4-positive T cells into Th(2)cells in vitro by the anti-CD3 plus IL-4 was completely suppressed by exogenously added IL-6, whereas Th(1)differentiation of T cells by the anti-CD3 plus IL-12 was not inhibited by the presence of IL-6. Thus, these results indicate that IL-6 physiologically could modulate qualitative T cell response and suggest that it augments Th(1)responses partly through its inhibitory capability of IL-4-induced Th(2)differentiation of naive T cells.

Inhibition of Th1 differentiation by IL-6 is mediated by SOCS1

Interleukin 6 (IL-6) is a cytokine produced by immune and nonimmune cells and exhibits functional pleiotropy and redundancy. IL-6 plays an important role in the differentiation of several cell types. Here, we describe a novel function of IL-6: the negative regulation of CD4+ Th1 cell differentiation. While IL-6-directed CD4+ Th2 differentiation is mediated by IL-4, inhibition of Th1 differentiation by IL-6 is independent of IL-4. IL-6 upregulates suppressor of cytokine signaling 1 (SOCS1) expression in activated CD4+ T cells, thereby interfering with signal transducer and activator of transcription 1 (STAT1) phosphorylation induced by interferon gamma (IFNgamma). Inhibition of IFNgamma receptor-mediated signals by IL-6 prevents autoregulation of IFNgamma gene expression by IFNgamma during CD4+ T cell activation, thereby preventing Th1 differentiation. Thus, IL-6 promotes CD4+ Th2 differentiation and inhibits Th1 differentiation by two independent molecular mechanisms.

Involvement of IL-6, apart from its role in immunity, in mediating a chronic response during experimental arthritis

Interleukin-6 (IL-6) is highly produced during arthritis but its exact function is still unknown. In this study we examined if IL-6, apart from its role in immunity, was involved in the local inflammatory response in experimental arthritis. IL-6 deficient (IL-6(-/-)) and wild-type mice were first compared in the antigen-induced arthritis model. IL-6 deficiency resulted in a mild, transient inflammation whereas wild-type mice developed a chronic, destructive synovitis. Wild-type mice immunized with one-tenth of the normal antigen dose still developed chronic arthritis despite low antibody levels, excluding reduced humoral immunity in IL-6(-/-) mice as a crucial phenomenon. In addition, passive immune-complex-induced arthritis did not differ between wild-type and IL-6(-/-) mice. Another option is reduced levels of Th1 cells in IL-6(-/-) mice. However, transfer of antigen-specific wild-type lymph node cells to IL-6(-/-) mice enhanced acute joint inflammation and increased cartilage damage but still could not sustain chronic inflammation, suggesting involvement of nonimmune elements of IL-6 activity in chronicity. In line with this, nonimmunologically mediated zymosan-induced arthritis developed similarly in the first week, but only wild-type mice developed chronic synovitis. These results indicate an important role for IL-6 in propagation of joint inflammation, potentially independent of its role in immunity.

Genetic dissection of primary and secondary responses to a widespread natural pathogen of the gut, Eimeria vermiformis

Because most pathogens initially challenge the body at epithelial surfaces, it is important to dissect the mechanisms that underlie T-cell responses to infected epithelial cells in vivo. The coccidian parasites of the genus Eimeria are protozoan gut pathogens that elicit a potent, protective immune response in a wide range of host species. CD4+ alpha beta T cells and gamma interferon (IFN-gamma) are centrally implicated in the primary immunoprotective response. To define any additional requirements for the primary response and to develop a comparison between the primary and the secondary response, we have studied Eimeria infections of a broad range of genetically altered mice. We find that a full-strength primary response depends on beta(2)-microglobulin (class I major histocompatibility complex [MHC] and class II MHC and on IFN-gamma and interleukin-6 (IL-6) but not on TAP1, perforin, IL-4, Fas ligand, or inducible nitric oxide synthetase. Indeed, MHC class II-deficient and IFN-gamma-deficient mice are as susceptible to primary infection as mice deficient in all alpha beta T cells. Strikingly, the requirements for a highly effective alpha beta-T-cell-driven memory response are less stringent, requiring neither IFN-gamma nor IL-6 nor class I MHC. The class II MHC dependence was also reduced, with adoptively transferable immunity developing in MHC class II(-/-) mice. Besides the improved depiction of an immune response to a natural gut pathogen, the finding that effective memory can be elicited in the absence of primary effector responses appears to create latitude in the design of vaccine strategies.

Endogenous and exogenous IL-6 inhibit aeroallergen-induced Th2 inflammation

Chronic Th2-dominated inflammation and exaggerated IL-6 production are characteristic features of the asthmatic airway. To understand the processes that are responsible for the chronicity of this response and the role(s) of IL-6 in the regulation of airway Th2 inflammation, we compared the responses induced by OVA in sensitized wild-type mice, IL-6 deficient (-/-) mice, and transgenic mice in which IL-6 was overexpressed in the airway (CC10-IL-6 mice). When compared with wild-type mice, IL-6-/- mice manifest exaggerated inflammation and eosinophilia, increased levels of IL-4, IL-5, and IL-13 protein and mRNA, exaggerated levels of eotaxin, JE/monocyte chemoattractant protein-1, macrophage inflammatory protein-1alpha and -2, and mRNA, increased bronchoalveolar lavage (BAL) TGF-beta1, and exaggerated airway responses to aerosolized methacholine. In contrast, CC10-IL-6 mice, on both C57BL/6 and BALB/c backgrounds, manifest diminished inflammation and eosinophilia, decreased levels of IL-4, IL-5, and IL-13 protein and mRNA, and decreased levels of bronchoalveolar lavage TGF-beta1. IL-6 also decreased the expression of endothelial VCAM-1 and airway responsiveness to methacholine in these animals. These alterations in the IL-6-/- and CC10-IL-6 mice were not associated with significant decreases or increases in the levels of IFN-gamma, respectively. These studies demonstrate that endogenous and exogenous IL-6 inhibit aeroallergen-induced Th2 inflammation and that this inhibition is not mediated by regulatory effects of IFN-gamma. IL-6 may be an important anti-inflammatory, counterregulatory, and healing cytokine in the airway.

Interleukin 18 restores defective Th1 immunity to Candida albicans in caspase 1-deficient mice

Caspase 1, formerly designated interleukin 1beta (IL-1beta)-converting enzyme, processes pro-IL-1beta and pro-IL-18 to yield active cytokines that play a pivotal role in inflammation and cell activation. We show here the effect of caspase 1 deficiency on the inflammatory and adaptive immune responses to the fungus Candida albicans. Caspase 1 deficiency did not affect susceptibility to primary systemic infection with the fungus, as revealed by survival and fungal growth. However, Th1-mediated resistance to reinfection was greatly impaired in caspase 1-deficient mice, and this correlated with low-level production of IL-12 and gamma interferon. Early in infection, production of these cytokines and that of tumor necrosis factor alpha, IL-6, and, interestingly, IL-1beta occurred normally in caspase 1-deficient mice, while that of IL-18 was severely impaired. Exogenous administration of IL-18, more than IL-12, restored the Th1-mediated resistance to the infection. We conclude that, while caspase 1 is not indispensable for release of mature IL-1beta in candidiasis, the caspase 1-dependent production of IL-18 may represent an important and novel pathway for the expression of sustained Th1 reactivity to the fungus.

Treatment with oxoglaucine can enhance host resistance to Candida albicans infection of mice with adjuvant arthritis

The alkaloid oxoglaucine reduced CD4+ cell clones in adult mice and decreased CD4+, CD8+ and Ig+ levels in newborn mice. It prevented the increase of CD8+ and Ig+ clones induced by Candida albicans (C. albicans) in adult mice. TNF-alpha serum accumulation was inhibited by oxoglaucine in C. albicans infection and adjuvant arthritis. Treatment with oxoglaucine of arthritic mice, followed by inoculation with C. albicans enhanced the host resistance against the pathogen.

Interleukin-6 is produced during both murine and avian Eimeria infections

The production of interleukin-6 (IL-6) during Eimeria infection was investigated in an attempt to gain a better understanding of the role of this multi-functional cytokine in resistance to this parasite. IL-6 production was measured in both chickens, in which the disease is of economic importance, and the better-characterised murine model system. Systemic and local IL-6 production in mice during E. vermiformis infection was investigated, in the relatively resistant BALB/c strain, and the relatively susceptible C57 BL/6 strain, using a murine IL-6 ELISA and the 7TD1 assay. Enhanced systemic production of IL-6 in serum was seen in infected BALB/c mice when compared to C57 BL/6 mice. This difference was also reflected in the draining lymph node of the site of infection, assessed by testing supernatants from stimulated mesenteric lymph node cells taken from infected mice at different times post-infection. Production of chicken IL-6-like factor activity was investigated using a murine IL-6 7TD1 bioassay. The presence of substantial quantities of IL-6-like factor activity was detected in serum taken from some chickens infected with E. tenella during the course of primary infection and, in a separate experiment, during the first few hours post-infection, a time when the pro-inflammatory capacity of IL-6 would influence the developing immune response. These results suggest that IL-6 is also important in the induction of immune effector responses to Eimeria infections in the chicken.

Interleukin-6 signal transduction and lymphocyte function

Interleukin-6 (IL-6) is a pleiotropic cytokine that acts on a wide variety of cell types. It has important regulatory functions in the immune system, is a mediator of the acute-phase response, and is involved in the regulation of differentiation, proliferation, and survival of target cells. A major signal transduction pathway for IL-6 involves activation of JAK kinases and the transcription factor Stat3. In addition, a great many of other signalling pathways are induced. Stat3 has been shown to be a central player of IL-6 signalling in many systems whereas the functions of most other IL-6-activated pathways are not yet understood. In this review, we discuss the current knowledge on IL-6 functions in the immune system, IL-6 signal transduction, and its significance for lymphocyte function.

Chemiluminescence activity in whole blood phagocytes of dogs naturally infected with Leishmania infantum

Dogs are the domestic reservoir of Leishmania infantum, a vector-borne intracellular protozoan agent of human visceral leishmaniasis. The role of polymorphonuclear leukocytes (PMNs) in the immune defence against this parasite has been poorly studied. We have investigated the function of peripheral blood PMNs in naive beagle dogs that have been naturally exposed to phlebotomine vectors in an area highly endemic for canine leishmaniasis, and found infected by Leishmania at the end of the transmission season. Whole blood phagocyte oxidative metabolism was assessed by a rapid method that determines a luminol-amplified chemiluminescence (CL) emission. This was evaluated using either a soluble stimulant, phorbol mirystate acetate (PMA), or phagocytic stimuli, such as zymosan unopsonized (ZYM) or opsonized with autologous serum (OPZ). In blood samples taken 2 months after exposure to Leishmania transmission, data on CL emission revealed a significant decrease of reactive oxygen intermediates (ROI) production in the presence of both PMA and ZYM, compared with blood samples obtained from dogs before exposure. On the contrary, no variations in CL emission were detected in presence of OPZ. Our data indicate that immunological changes occur early in canine leishmaniasis and confirm that the role of PMNs and their products need to be clarified.

Interleukin-6-deficient mice refractory to IgA dysregulation but not anorexia induction by vomitoxin (deoxynivalenol) ingestion

Dietary exposure to the trichothecene vomitoxin (VT) causes feed refusal and elevates IgA production in the mouse. Based on the observations that IL-6 can cause anorexia and promote IgA production and that gene expression of this cytokine is increased in vivo and ex vivo on VT exposure, we hypothesized that IL-6 is an essential cytokine in VT-induced feed refusal and IgA dysregulation. To test this hypothesis, the effects of dietary VT on feed intake, weight gain, serum IgA levels and kidney mesangial IgA deposition in an IL-6-"knockout" mouse (B6129-IL6(tmi Kopf)) were compared to those in both a corresponding "wildtype" (B6129F2) and a previously characterized "sentinel" strain (B6C3F1) that possess the intact gene for this cytokine. IL-6 deficiency did not alter the capacity of VT to cause feed refusal or impair weight gain. VT-fed B6129F2 and B6C3F1 mice had significantly higher serum IgA concentrations than did their corresponding controls fed clean diet, whereas significant differences were not observed between IL-6 KO mice fed VT or control diets. Kidneys taken from VT-fed wild-type and sentinel mice had significantly increased mesangial IgA deposition as compared to controls. While slight increases in mesangial IgA were observed in VT-fed IL-6 KO mice, mean fluorescence intensities were significantly less than that found in the corresponding wild-type and sentinel strains. IL-6 KO mice appeared to be less prone to the development of microscopic haematuria following VT exposure than were the corresponding wild-type and sentinel strains. In total, the results suggested that IL-6-deficient mice were refractory to VT-induced dysregulation of IgA production and development of IgA nephropathy, whereas chronic VT-mediated nutritional effects related to feed intake and weight gain were unaffected.

Enhancement of Th2 response in IL-6-deficient mice immunized with myelin oligodendrocyte glycoprotein

To investigate the mechanism for the resistance of IL-6-deficient mice to experimental autoimmune encephalomyelitis (EAE), we examined the production of cytokines in lymph nodes (LNs) of wild-type and IL-6-deficient mice immunized with myelin oligodendrocyte glycoprotein (MOG) by reverse transcriptase-polymerase chain reaction analysis. Significant up-regulation of IL-4 production and down-regulation of IFN-gamma production were found in LNs from IL-6-deficient mice as compared to LNs from wild-type mice. Administration of IL-6, which caused typical EAE in IL-6-deficient mice immunized with MOG, reduced IL-4 production but did not restore IFN-gamma production in LNs of IL-6-deficient mice. These results implied that the resistance of IL-6-deficient mice to EAE might be mainly due to enhancement of Th2 response.

Interleukin-6 induces early gamma interferon production in the infected lung but is not required for generation of specific immunity to Mycobacterium tuberculosis infection

Immunity to Mycobacterium tuberculosis is dependent upon the generation of a protective gamma interferon (IFN-gamma)-producing T-cell response. Recent studies have suggested that interleukin-6 (IL-6) is required for the induction of a protective T-cell response and that IL-4 may suppress the induction of IFN-gamma. To evaluate the role of the cytokines IL-6 and IL-4 in the generation of pulmonary immunity to M. tuberculosis, IL-6 and IL-4 knockout mice were infected with M. tuberculosis via aerosol. The absence of IL-6 led to an early increase in bacterial load with a concurrent delay in the induction of IFN-gamma. However, mice were able to contain and control bacterial growth and developed a protective memory response to secondary infection. This demonstrates that while IL-6 is involved in stimulating early IFN-gamma production, it is not essential for the development of protective immunity against M. tuberculosis. In contrast, while the absence of IL-4 resulted in increased IFN-gamma production, this had no significant effect upon bacterial growth.

Protective immunity to rotavirus shedding in the absence of interleukin-6: Th1 cells and immunoglobulin A develop normally

We investigated whether interleukin-6 (IL-6) was required for the development of immunoglobulin A (IgA)- and T-helper 1 (Th1)-associated protective immune responses to rotavirus by using adult IL-6-deficient mice [BALB/c and (C57BL/6 x O1a)F(2) backgrounds]. Naive IL-6(-) mice had normal frequencies of IgA plasma cells in the gastrointestinal tract. Consistent with this, total levels of IgA in fecal extracts, saliva, and sera were unaltered. In specific response to oral infection with rhesus rotavirus, IL-6(-) and IL-6(+) mice exhibited efficient Th1-type gamma interferon responses in Peyer's patches with high levels of serum IgG2a and intestinal IgA. Although there was an increase in Th2-type IL-4 in CD4(+) T cells from IL-6(-) mice following restimulation with rotavirus antigen in the presence of irradiated antigen-presenting cells, unfractionated Peyer's patch cells failed to produce a significant increase in IL-4. Moreover, virus-specific IgG1 in serum was not significantly increased in IL-6(-) mice in comparison with IL-6(+) mice. Following oral inoculation with murine rotavirus, IL-6(-) and IL-6(+) mice mediated clearance of rotavirus and mounted a strong IgA response. When IL-6(-) and IL-6(+) mice [(C57BL/6 x O1a)F(2) background] were orally inoculated with rhesus rotavirus and later challenged with murine rotavirus, all of the mice maintained high levels of IgA in feces and were protected against reinfection. Thus, IL-6 failed to provide unique functions in the development of IgA-secreting B cells and in the establishment of Th1-associated protective immunity against rotavirus infection in adult mice.

Roles of STAT3 in mediating the cell growth, differentiation and survival signals relayed through the IL-6 family of cytokine receptors

Members of the IL-6 cytokine family are involved in a variety of biological responses, including the immune response, inflammation, hematopoiesis, and oncogenesis by regulating cell growth, survival, and differentiation. These cytokines use gp130 as a common receptor subunit. The binding of ligand to gp130 activates the JAK/STAT signal transduction pathway, where STAT3 plays a central role in transmitting the signals from the membrane to the nucleus. STAT3 is essential for gp130-mediated cell survival and G1 to S cell-cycle-transition signals. Both c-myc and pim have been identified as target genes of STAT3 and together can compensate for STAT3 in cell survival and cell-cycle transition. STAT3 is also required for gp130-mediated maintenance of the pluripotential state of proliferating embryonic stem cells and for the gp130-induced macrophage differentiation of M1 cells. Furthermore, STAT3 regulates cell movement, such as leukocyte, epidermal cell, and keratinocyte migration. STAT3 also appears to regulate B cell differentiation into antibody-forming plasma cells. Since the IL-6/gp130/STAT3 signaling pathway is involved in both B cell growth and differentiation into plasma cells it is likely to play a central role in the generation of plasma cell neoplasias. Oncogene (2000).

The role of IL-6 in the inflammatory and humoral response to adenoviral vectors

BACKGROUND

The major concern for the use of adenoviral vectors for gene therapy is the viral-induced immune response that has been shown to be responsible for short-term transgene expression and inefficient viral readministration. In vivo studies and clinical trials with recombinant adenovirus have suggested a role for interleukin 6 (IL-6) in the inflammatory reaction that follows Ad-infection. IL-6 plays an important role in the acute-phase innate response, in the differentiation of B-cells and in the activation of the Th2 cell subsets.

METHODS

To clarify the role of IL-6 in the immune response to Ad-vectors, we used IL-6 knock-out mice (IL-6 -/- ). E1/E3 deleted recombinant adenoviruses encoding reporter genes were administered to wild type or IL-6-/- mice; transgene expression kinetics and immune response were analyzed.

RESULTS

Acute phase protein production was significantly diminished in IL-6 -/- mice after adenoviral injection. No significant difference between wild type and knock-out animals in the level or the nature of leucocyte recruitment in the liver was detectable. A minor decrease in the IgG response to Ad-recombinants was observed in knock-out mice. Gene transfer efficiency, both in terms of levels and duration of transgene expression, were comparable in IL-6+/+ and IL-6-/- mice. An increase in IL-1beta and tumor necrosis factor-alpha (TNF-alpha) levels was observed in the sera of IL-6 -/- mice as compared to wild type animals: this phenomenon represents a possible compensatory mechanism for the establishment of the immune phenotype observed in mutant mice.

CONCLUSIONS

IL-6 plays a role in the acute phase response to adenoviral vectors. Nevertheless, possibly due to a compensatory mechanism exerted by other cytokines, the antibody and cellular responses to adenoviruses are very similar in wild type and IL-6 -/- mice.

Activation of peripheral phagocytes in BCG-vaccinated subjects

The role of polymorphonuclear leukocytes (PMNs) in the immune defence against intracellular bacteria has long been neglected. Only recently have studies begun to address this issue. In this study the behavior of peripheral PMNs in Bacillus Calmette-Guerin (BCG) vaccinated subjects was investigated. Twenty healthy and purified protein derivative-negative adults were studied before, and two and four months after, BCG administration. Luminol-amplified chemiluminescence (CL) emission was evaluated in whole blood phagocytes using a soluble stimulus, such as phorbol mirystate acetate, or particulates such as zymosan opsonized with homologous (OZH) or autologous (OZA) serum. Specific IgG, IgA and IgM against antigen -60 by ELISA, total immunoglobulin, C3 and C4 components of complement, were assessed by immunochemical tests. The results revealed a late heightened production of reactive oxygen intermediates in vaccinated subjects in presence of OZA and OZH. Our findings confirm that the role of PMNs and their mediators in immunoregulation of intracellular diseases needs to be re-evaluated.

Dissection of signaling cascades through gp130 in vivo: reciprocal roles for STAT3- and SHP2-mediated signals in immune responses

We generated a series of knockin mouse lines, in which the cytokine receptor gp130-dependent STAT3 and/or SHP2 signals were disrupted, by replacing the mouse gp130 gene with human gp130 mutant cDNAs. The SHP2 signal-deficient mice (gp130F759/F759 were born normal but displayed splenomegaly and lymphadenopathy and an enhanced acute phase reaction. In contrast, the STAT3 signal-deficient mice (gp130FXQ/FXXQ) died perinatally, like the gp130-deficient mice (gp130D/D). The gp130F759/F759 mice showed prolonged gp130-induced STAT3 activation, indicating a negative regulatory role for SHP2. Th1-type cytokine production and IgG2a and IgG2b production were increased in the gp130F759/F759 mice, while they were decreased in the gp130FXXQ/FXXQ immune system. These results indicate that the balance of positive and negative signals generated through gp130 regulates the immune responses.

Modulation of neutrophil function in host defense against disseminated Candida albicans infection in mice

Neutrophils (PMNs) constitute the main mechanism of host defense against acute invasive and disseminated candidiasis. Recent studies have demonstrated that tumor necrosis factor-alpha (TNFalpha), interleukin-6 (IL-6) and granulocyte colony-stimulating factor (G-CSF) play an important role in the recruitment of PMNs at the site of invasive Candida infection. In the absence of either TNFalpha or IL-6, the course of experimental disseminated candidiasis is more severe, due to defective PMN recruitment. Treatment of mice with recombinant G-CSF (rG-CSF) leads to a significantly reduced mortality during disseminated candidiasis. The outgrowth of Candida albicans from the organs of rG-CSF-treated mice is significantly decreased. Treatment with the combination of rG-CSF and fluconazole has an additive effect on the reduction of fungal load in the organs. In subacute or chronic disseminated Candida infection, rG-CSF is less effective, indicating that neutrophil recruitment and activation are crucial in acute, life-threatening candidiasis, whereas other host defense mechanisms control the outcome of less overwhelming invasive Candida infection.

Increased susceptibility to systemic candidiasis in interleukin-6 deficient mice

Interleukin-6 (IL-6) is a multifunctional cytokine that regulates multiple aspects of the innate immune response. It has been recently shown that endogenous IL-6 is crucial for an efficient defence against severe infections with Gram-negative and Gram-positive bacteria. The aim of the present study was to investigate the role of endogenous IL-6 in the defence against infection with the yeast Candida albicans. During experimental candidemia, IL-6 deficient mice (IL-6-/-) had a decreased survival and an increased fungal load in their organs when compared with IL-6+/+ controls, despite increased plasma concentrations of tumour necrosis factor-alpha (TNF), interleukin-1 alpha (IL-1 alpha) and IL-1 beta, IL-6-/- mice were not able to mount an efficient neutrophil response during the infection. When mice were rendered neutropenic by cyclophosphamide, neutropenic IL-6-/- mice were equally susceptible to C. albicans when compared to neutropenic IL-6+/+ mice, implying that neutrophils mediate the beneficial effect of endogenous IL-6. In conclusion, IL-6-/- mice are more susceptible to disseminated candidiasis, and the effect of IL-6 is most likely mediated by neutrophils.

IL-6 plays a crucial role in the induction phase of myelin oligodendrocyte glucoprotein 35-55 induced experimental autoimmune encephalomyelitis

We investigated the role of IL-6 in myelin oligodendrocyte glycoprotein (MOG) peptide induced experimental autoimmune encephalomyelitis (EAE) using IL-6-deficient mice and found that IL-6-deficient mice were resistant to active induction of EAE, but that the treatment of those mice with IL-6 during the preclinical phase caused typical EAE. We also found that both wild-type and IL-6-deficient mice were resistant to passive transfer of EAE by lymphocytes from IL-6-deficient mice, but that passive transfer of lymphocytes from wild-type mice induced typical EAE in IL-6-deficient mice. Histological abnormalities of the central nervous system (CNS) in those IL-6-deficient mice with EAE were similar to those in wild-type mice with EAE. Reverse transcriptase-polymerase chain reaction (RT-PCR) analysis revealed no difference in the production of inflammatory cytokines such as IL-1beta, IL-2, TNF-alpha, and IFN-gamma in the CNS of IL-6-deficient mice with EAE as compared to the CNS of wild-type mice with EAE. These results indicated that IL-6 might be an important factor in the induction phase, but might have little influence on the effector phase of EAE. We further estimated the production of cytokines in MOG-stimulated lymph node (LN) cells by enzyme-linked immunosorbent assay. Increased IL-4 and IL-10 production and reduced IL-2 and IFN-gamma production were observed in LN cells from IL-6-deficient mice as compared to LN cells from wild-type mice. These results suggested that a shift of T cell responses from Thl to Th2 might explain the resistance of IL-6-deficient mice to EAE. Taken together, IL-6 may play a crucial role in the induction phase of EAE by modulating Th1/Th2 balance.

Interleukin-6 and interleukin-12 participate in induction of a type 1 protective T-cell response during vaccination with a tuberculosis subunit vaccine

We examined the role of cytokines in the development of gamma interferon (IFN-gamma)-secreting protective T cells following immunization with a culture filtrate subunit vaccine against Mycobacterium tuberculosis containing the adjuvant dimethyldioctadecylammonium bromide (DDA). Depletion of either interleukin-6 (IL-6) or IL-12 with specific neutralizing antibodies during vaccination reduced the priming of T cells for antigen-specific proliferation and IFN-gamma secretion. Such reduction was also observed in IL-6 gene-disrupted mice as compared to wild-type animals. IL-6 was found to play a role in the initial differentiation of Th1 cells but not in their expansion. The defect found after IL-6 depletion or in IL-6-knockout mice was compensated by the inclusion of recombinant mouse IL-12 in the vaccine. The induction of protective immunity against an intravenous or an aerosol challenge with live, virulent M. tuberculosis was markedly reduced by neutralizing either IL-6 or IL-12 during immunization with the vaccine. Likewise, the effects of IL-6 neutralization were partially reversed by including IL-12 in the vaccine. Our data point to an important role of IL-6 and IL-12 in the generation of cell-mediated immunity to tuberculosis.

Increased Susceptibility of TNF-α Lymphotoxin-α Double Knockout Mice to Systemic Candidiasis Through Impaired Recruitment of Neutrophils and Phagocytosis of Candida albicans

TNF-α and lymphotoxin-α (LT) are members of the TNF family, and these cytokines play crucial roles in the defense against infection with Candida albicans. The aim of the present study was to investigate the role of endogenous TNF and LT during disseminated candidiasis in TNF−/−LT−/− knockout mice. The TNF- and LT-deficient animals had a significantly increased mortality following C. albicans infection compared with control mice, and this was due to a 10- to 1000-fold increased outgrowth of the yeast in their organs. No differences between TNF−/−LT−/− mice and TNF+/+LT+/+ were observed when mice were rendered neutropenic, suggesting that activation of neutrophils mediates the beneficial effects of endogenous TNF and LT. Histopathology of the organs, combined with neutrophil recruitment experiments, showed a dramatic delay in the neutrophil recruitment at the sites of Candida infection in the TNF−/−LT−/− mice. Moreover, the neutrophils of deficient animals were less potent to phagocytize Candida blastospores than control neutrophils. In contrast, the killing of Candida and the oxygen radical production did not differ between neutrophils of TNF−/−LT−/− and TNF+/+LT+/+ mice. Peak circulating IL-6 was significantly higher in TNF−/−LT−/− mice during infection. Peritoneal macrophages of TNF−/−LT−/− mice did not produce TNF, and synthesized significantly lower amounts of IL-1α, IL-1β, IL-6, and macrophage-inflammatory protein-1α than macrophages of TNF+/+LT+/+ animals did. In conclusion, endogenous TNF and/or LT contribute to host resistance to disseminated candidiasis, and their absence in TNF−/−LT−/− mice renders the animals susceptible through impaired recruitment of neutrophils and impaired phagocytosis of C. albicans.

Delayed onset and reduced severity of collagen-induced arthritis in interleukin-6-deficient mice

OBJECTIVE

To investigate the roles of interleukin-6 (IL-6) in the pathogenesis of rheumatoid arthritis (RA) by studying its effect on murine collagen-induced arthritis (CIA).

METHODS

IL-6-deficient (IL-6-/-) mice with a genetic background of susceptibility to CIA were generated by backcrossing them with DBA/1J mice for 8 generations. Clinical and immunologic features were compared between these mice and IL-6 wild-type (IL-6+/+) littermates with CIA.

RESULTS

Serum IL-6 levels increased during the development of CIA in IL-6+/+ mice. Two prominent peaks were observed. The first was coincident with the onset of arthritis, and the second one was observed during exacerbation of the disease. The onset of arthritis in IL-6-/- mice was delayed for 2 weeks compared with that in IL-6+/+ mice, and the severity of arthritis, as indicated by the arthritis score, remained significantly lower in IL-6-/- mice during the entire followup period (14 weeks), although all IL-6-/- mice developed definite arthritis as did the IL-6+/+ mice. Histologic severity was also reduced in IL-6-/- mice. In addition, radiologic changes such as osteopenia and bone erosion were reduced significantly in these animals. Both humoral and cellular responses to type II collagen (CII) in IL-6-/- mice were reduced to about half those in IL-6+/+ mice. In addition, enhanced production of IL-4 and IL-10 in response to concanavalin A stimulation was observed in IL-6-/- mice.

CONCLUSION

IL-6 plays an important role in the development of CIA, and both suppression of specific immune responses to CII and a tendency to a shift toward a Th2 cytokine profile might contribute in part to the attenuation of CIA in IL-6-/- mice. These findings suggest that blockade of IL-6 might be beneficial in the treatment of RA.

Protection by Group II Phospholipase A2 Against Staphylococcus aureus

Group II phospholipase A2 (PLA2) is an enzyme that has marked antibacterial properties in vitro. To define the role of group II PLA2 in the defense against Staphylococcus aureus, we studied host responses in transgenic mice expressing human group II PLA2 and group II PLA2-deficient C57BL/6J mice in experimental S. aureus infection. After the administration of S. aureus, the transgenic mice showed increased expression of group II PLA2 mRNA in the liver and increased concentration of group II PLA2 in serum, whereas the PLA2-deficient mice completely lacked the PLA2 response. Expression of human group II PLA2 resulted in reduced mortality and improved the resistance of the mice by killing the bacteria as indicated by low numbers of live bacteria in their tissues. Human group II PLA2 was responsible for the bactericidal activity of transgenic mouse serum. These results suggest a possible role for group II PLA2 in the innate immunity against S. aureus infection.

Effects of cytokines and endotoxin on the intracellular growth of bacteria

Patients with unresolving acute respiratory distress syndrome (ARDS) have persistently elevated levels of proinflammatory cytokines in the lungs and circulation and increased rates of bacterial infections. Phagocytic cells hyperactivated with lipopolysaccharide (LPS), which induces high levels of proinflammatory cytokines in monocytic cells, are inefficient in killing ingested bacteria despite having intact phagocytic activity. On the other hand, phagocytic cells that are activated with an analogue of LPS that does not induce the expression of proinflammatory cytokines effectively ingest and kill bacteria. We hypothesized that in the presence of high concentrations of proinflammatory cytokines, bacteria may adapt and utilize cytokines to their growth advantage. To test our hypothesis, we primed a human monocytic cell line (U937) with escalating concentrations of the proinflammatory cytokines tumor necrosis factor alpha, interleukin-1beta (IL-1beta), and IL-6 and with LPS. These cells were then exposed to fresh isolates of three common nosocomial pathogens: Staphylococcus aureus, Pseudomonas aeruginosa, and an Acinetobacter sp. In human monocytes primed with lower concentrations of proinflammatory cytokines (10 to 250 pg) or LPS (1 and 10 ng), intracellular bacterial growth decreased. However, when human monocytes were primed with higher concentrations of proinflammatory cytokines (1 to 10 ng) or LPS (1 to 10 micrograms), intracellular growth of the tested bacteria increased significantly (P <0.0001). These results were reproduced with peripheral blood monocytes obtained from normal healthy volunteers. The specificity of the cytokine activity was demonstrated by neutralizing the cytokines with specific antibodies. Our findings provide a possible mechanism to explain the frequent development of bacterial infections in patients with an intense and protracted inflammatory response.

Expression of interleukin-6 in the cornea in response to infection with different strains of Pseudomonas aeruginosa

Strains of Pseudomonas aeruginosa causing keratitis can be either cytotoxic (6206) or invasive (6294), while a strain (Paer1) causing contact lens-induced acute red eye has been shown to be neither. In situ hybridization was used to examine the location and identity of cells expressing interleukin-6 (IL-6) mRNA in the murine cornea and changes in expression in response to infection with different strains of P. aeruginosa. The number of IL-6-positive cells was determined by image analysis. IL-6 protein levels were measured by an enzyme-linked immunosorbent assay. BALB/c mice were challenged by use of the wounded-cornea model with P. aeruginosa 6294, 6206, or Paer1 (2 x 10(6) CFU). At time intervals up to 24 h, postchallenge corneal tissue was probed for IL-6 mRNA. IL-6 mRNA expression was rapidly elevated in the epithelium in response to strains 6294 and 6206. At the conclusion of the experiments, infiltrating inflammatory cells also stained positively for IL-6 mRNA. In contrast, corneas challenged with strain Paer1 showed significant upregulation of IL-6 mRNA only at 4 h postchallenge. Three distinct patterns of IL-6 mRNA expression in the mouse cornea occur in response to these three ocular isolates of P. aeruginosa. The data obtained for mRNA expression in the cornea for all three strains of P. aeruginosa correlated well with IL-6 protein analysis of whole-eye homogenates. Differences in the cytokine responses to these strains correlate with differences in the pathology associated with each strain and may offer an opportunity to develop strategies for the improved management of ocular inflammation.

Immune-Stimulating Complexes Induce an IL-12-Dependent Cascade of Innate Immune Responses

The development of subunit vaccines requires the use of adjuvants that act by stimulating components of the innate immune response. Immune-stimulating complexes (ISCOMS) containing the saponin adjuvant Quil A are potential vaccine vectors that induce a wide range of Ag-specific responses in vivo encompassing both humoral and CD4 and CD8 cell-mediated immune responses. ISCOMS are active by both parenteral and mucosal routes, but the basis for their adjuvant properties is unknown. Here we have investigated the ability of ISCOMS to recruit and activate innate immune responses as measured in peritoneal exudate cells. The i.p. injection of ISCOMS induced intense local inflammation, with early recruitment of neutrophils and mast cells followed by macrophages, dendritic cells, and lymphocytes. Many of the recruited cells had phenotypic evidence of activation and secreted a number of inflammatory mediators, including nitric oxide, reactive oxygen intermediates, IL-1, IL-6, IL-12, and IFN-γ. Of the factors that we investigated further only IL-12 appeared to be essential for the immunogenicity of ISCOMS, as IL-6- and inducible nitric oxide synthase knockout (KO) mice developed normal immune responses to OVA in ISCOMS, whereas these responses were markedly reduced in IL-12KO mice. The recruitment of peritoneal exudate cells following an injection of ISCOMS was impaired in IL-12KO mice, indicating a role for IL-12 in establishing the proinflammatory cascade. Thus, ISCOMS prime Ag-specific immune responses at least in part by activating IL-12-dependent aspects of the innate immune system.

Loss of a gp130 cardiac muscle cell survival pathway is a critical event in the onset of heart failure during biomechanical stress

Biomechanical stress is a major stimulus for cardiac hypertrophy and the transition to heart failure. By generating mice that harbor a ventricular restricted knockout of the gp130 cytokine receptor via Cre-IoxP-mediated recombination, we demonstrate a critical role for a gp130-dependent myocyte survival pathway in the transition to heart failure. Such conditional mutant mice have normal cardiac structure and function, but during aortic pressure overload, these mice display rapid onset of dilated cardiomyopathy and massive induction of myocyte apoptosis versus the control mice that exhibit compensatory hypertrophy. Thus, cardiac myocyte apoptosis is a critical point in the transition between compensatory cardiac hypertrophy and heart failure. gp130-dependent cytokines may represent a novel therapeutic strategy for preventing in vivo heart failure.

Oncostatin M transforms lymphoid tissue function in transgenic mice by stimulating lymph node T-cell development and thymus autoantibody production

Oncostatin M (OM) is a member of the IL-6 subfamily of cytokines that is expressed in primary lymphoid tissues such as bone marrow and thymus, as well as in secondary lymphoid tissues and activated leukocytes. We produced transgenic mice that overexpressed the human, bovine, or mouse OM genes and compared their relative ability to modulate lymphopoiesis. Each species of cytokine induced a similar extrathymic pathway of T-cell development involving the accumulation of immature T cells within lymph nodes. Reconstitution experiments utilizing lethally irradiated athymic mice indicated that OM had caused hematopoietic precursors within fetal liver and bone marrow to initiate lymph node T-cell development in the absence of a thymic environment. Breeding experiments with IL6-/- and IL-7r(alpha)-/- deficient mice, indicated that induction of this extrathymic pathway by the OM transgene occurred in the absence of IL-6, but was strictly dependent on IL-7 receptor signaling. Separately, OM stimulated the accumulation of immature B cells within the transgenic thymus and caused the subcapsular regions of the thymus to expand with mature B and T cells. This thymus conversion to secondary lymphoid tissue was responsible for a lethal autoimmune-like disease marked by high titers of circulating autoantibodies, proteinuria, and glomerulonephritis. The conserved phenotypes elicited by these three forms of OM indicate that this potent hematopoietic cytokine can regulate lymphoid tissue function and morphogenesis.

IL-12 Is an Effective Adjuvant for Induction of Mucosal Immunity

We addressed the effects of two cytokines, IL-6 and IL-12, derived from APCs, for the development of mucosal IgA Ab responses following their nasal delivery with the protein vaccine tetanus toxoid (TT). Mice treated nasally with IL-6 and TT showed higher TT-specific serum IgG (mainly IgG1 and IgG2b) Ab responses than did control mice, but exhibited no IgE and negligible secretory IgA (S-IgA) Ab responses. In contrast, IL-12 administered nasally with TT not only induced sharp increases in TT-specific serum IgG (mainly IgG1 and IgG2b) and IgA, but also elevated mucosal S-IgA Ab responses. Coadministration of IL-6 and IL-12 with TT did not enhance the mucosal or serum Ab responses over those seen with IL-12 alone. TT-specific CD4+ T cells from mice given TT with IL-6 or IL-12 produced higher levels of IFN-γ, IL-6, and IL-10 than did those from control mice, but only negligible levels of IL-4 and IL-5. In summary, both intranasal IL-6 and IL-12 induced serum Abs that protected mice from systemic challenge with TT, whereas only IL-12 induced mucosal S-IgA Ab responses. The significance of IL-12-induced Th1-type responses for regulation of both mucosal and systemic immunity is discussed.

IL-10 Is Required for Development of Protective Th1 Responses in IL-12-Deficient Mice upon Candida albicans Infection

IL-12 is both required and prognostic for Th1 development in mice with Candida albicans infection. To delineate further the physiologic role of IL-12 in antifungal immunity, mice deficient for this cytokine were assessed for susceptibility to C. albicans infections, and for parameters of innate and adaptive immunity. IL-12-deficient mice were highly susceptible to gastrointestinal infection or to reinfection and showed elevated production of Candida-specific IgE and IL-4 and defective production of IFN-γ. The failure to mount protective Th1 responses occurred despite the presence of an unimpaired innate antifungal immune response, which correlated with unaltered IFN-γ production, but defective production of, and responsiveness to, inhibitory IL-10. IL-10 or IL-12 neutralization increased the innate antifungal resistance in wild-type mice. However, in IL-12-deficient mice, treatment with exogenous IL-12 or IL-10 impaired IL-4 production and increased resistance to infection, through a negative effect on the CTLA-4/B7-2 costimulatory pathway. These results confirm the obligatory role of IL-12 in the induction of anticandidal Th1 responses, and indicate the existence of a positive regulatory loop between IL-12 and IL-10 that may adversely affect the innate antifungal response, but is required for optimal costimulation of IL-12-dependent CD4+Th1 cells.

The role of polymorphonuclear leukocytes in the resistance to cutaneous Leishmaniasis

The massive infiltration by polymorphonuclear leukocytes (PMN) soon after skin infection with Leishmania major suggests that PMN could participate in reducing parasite load and controlling the spreading of leishmanial infection. Yet, direct evidence for the participation of PMN in host defense against L. major was lacking. We investigated L. major infection in susceptible and resistant mice treated with the monoclonal (mAb) antibody RB6-8C5 that depletes the population of mature neutrophils and eosinophils. Both BALB/c and C57BL/6 mice depleted of PMN show accelerated parasite spreading and more severe footpad swelling than similarly infected untreated mice. In addition, significant higher parasite numbers were found in the lesion draining lymph nodes from PMN-depleted C57BL/6 mice. Histopathological analysis of the paw confirmed neutrophils containing ingested parasites as the dominant cell type in the infiltrate of the first days after infection and the nearly absolute neutrophil depletion in mAb-treated mice. Our data show the importance of PMN in early control of parasite load and parasitism spreading in cutaneous leishmaniasis.

Postnatally induced inactivation of gp130 in mice results in neurological, cardiac, hematopoietic, immunological, hepatic, and pulmonary defects

The pleiotrophic but overlapping functions of the cytokine family that includes interleukin (IL)-6, IL-11, leukemia inhibitory factor, oncostatin M, ciliary neurotrophic factor, and cardiotrophin 1 are mediated by the cytokine receptor subunit gp130 as the common signal transducer. Although mice lacking individual members of this family display only mild phenotypes, animals lacking gp130 are not viable. To assess the collective role of this cytokine family, we inducibly inactivated gp130 via Cre-loxP-mediated recombination in vivo. Such conditional mutant mice exhibited neurological, cardiac, hematopoietic, immunological, hepatic, and pulmonary defects, demonstrating the widespread importance of gp130-dependent cytokines.

Interleukin 6 influences germinal center development and antibody production via a contribution of C3 complement component

Mice rendered deficient for interleukin (IL) 6 by gene targeting were evaluated for their response to T cell-dependent antigens. Antigen-specific immunoglobulin (Ig)M levels were unaffected whereas all IgG isotypes showed varying degrees of alteration. Germinal center reactions occurred but remained physically smaller in comparison to those in the wild-type mice. This concurred with the observations that molecules involved in initial signaling events leading to germinal center formation were not altered (e.g., B7.2, CD40 and tumor necrosis factor R1). T cell priming was not impaired nor was a gross imbalance of T helper cell (Th) 1 versus Th2 cytokines observed. However, B7.1 molecules, absent from wild-type counterparts, were detected on germinal center B cells isolated from the deficient mice suggesting a modification of costimulatory signaling. A second alteration involved impaired de novo synthesis of C3 both in serum and germinal center cells from IL-6-deficient mice. Indeed, C3 provided an essential stimulatory signal for wild-type germinal center cells as both monoclonal antibodies that interrupted C3-CD21 interactions and sheep anti-mouse C3 antibodies caused a significant decrease in antigen-specific antibody production. In addition, germinal center cells isolated from C3-deficient mice produced a similar defect in isotype production. Low density cells with dendritic morphology were the local source of IL-6 and not the germinal center lymphocytes. Adding IL-6 in vitro to IL-6-deficient germinal center cells stimulated cell cycle progression and increased levels of antibody production. These findings reveal that the germinal center produces and uses molecules of the innate immune system, evolutionarily pirating them in order to optimally generate high affinity antibody responses.