Gregory J. Bagby

Cutting Edge: Roles of Toll-Like Receptor 4 and IL-23 in IL-17 Expression in Response to Klebsiella pneumoniae Infection

Local production of IL-17 is a significant factor in effective host defense against Gram-negative bacteria. However, the proximal events mediating IL-17 elaboration by T cells remain unclear. In this study, we show in vivo that intact Toll-like receptor 4 signaling in the lung is required for induction of both the p19 transcript of IL-23 and IL-17 protein elaboration in response to Klebsiella pneumoniae. Although IL-17 is widely considered a CD4+ T cell product, we also demonstrate significant in vitro IL-17 production by CD8+ T cells after culture in medium from dendritic cells exposed to these bacteria. The dominant portion of this IL-17-inducing activity for both CD4+ and CD8+ T cells is IL-23. These data demonstrate the critical signaling pathway for IL-17 induction in the host response to Gram-negative pulmonary infection and suggest a direct role for IL-23 in CD8+ T cell IL-17 production.

Innate immunity and pulmonary host defense

Acknowledgments:

Tumor necrosis factor-alpha mediates changes in tissue protein turnover in a rat cancer cachexia model.

Rats bearing the Yoshida AH-130 ascites hepatoma showed enhanced fractional rates of protein degradation in gastrocnemius muscle, heart, and liver, while fractional synthesis rates were similar to those in non-tumor bearing rats. This hypercatabolic pattern was associated with marked perturbations of the hormonal homeostasis and presence of tumor necrosis factor in the circulation. The daily administration of a goat anti-murine TNF IgG to tumor-bearing rats decreased protein degradation rates in skeletal muscle, heart, and liver as compared with tumor-bearing rats receiving a nonimmune goat IgG. The anti-TNF treatment was also effective in attenuating early perturbations in insulin and corticosterone homeostasis. Although these results suggest that tumor necrosis factor plays a significant role in mediating the changes in protein turnover and hormone levels elicited by tumor growth, the inability of such treatment to prevent a reduction in body weight implies that other mediators or tumor-related events were also involved.

Requirement of endogenous stem cell factor and granulocyte-colony-stimulating factor for IL-17-mediated granulopoiesis.

IL-17 is a novel, CD4+ T cell-restricted cytokine. In vivo, it stimulates hematopoiesis and causes neutrophilia consisting of mature granulocytes. In this study, we show that IL-17-mediated granulopoiesis requires G-CSF release and the presence or induction of the transmembrane form of stem cell factor (SCF) for optimal granulopoiesis. However, IL-17 also protects mice from G-CSF neutralization-induced neutropenia. G-CSF neutralization completely reversed IL-17-induced BM progenitor expansion, whereas splenic CFU-GM/CFU-granulocyte-erythrocyte-megakaryocyte-monocyte was only reduced by 50% in both Sl/Sld and littermate control mice. Thus, there remained a significant SCF/G-CSF-independent effect of IL-17 on splenic granulopoiesis, resulting in a preservation of mature circulating granulocytes. IL-17 is a cytokine that potentially interconnects lymphocytic and myeloid host defense and may have potential for therapeutic development.

Alcohol suppresses lipopolysaccharide-induced tumor necrosis factor activity in serum and lung

Ethanol intoxication has been shown to suppress selected functions of the immune system thereby compromising host defense against bacterial infections. Tumor necrosis factor, a secretory protein produced by the macrophage in response to lipopolysaccharide, mediates the inflammatory cascade and stimulates phagocyte functions. Acute ethanol intoxication markedly suppressed both serum and lung tumor necrosis factor elicited in response to lipopolysaccharide. Furthermore, ethanol inhibited intratracheal lipopolysaccharide-induced neutrophil recruitment into the alveoli and prevented the fall in circulating neutrophils in response to intravenous lipopolysaccharide. Thus, the anti-inflammatory effects of ethanol may be secondary to suppression of macrophage-derived tumor necrosis factor.

Pentoxifylline inhibits lipopolysaccharide-induced serum tumor necrosis factor and mortality

Tumor necrosis factor, a mononuclear phagocyte-derived peptide produced in response to lipopolysaccharide, has been shown to mediate certain aspects of septic shock and multiple organ failure resulting from gram-negative septicemia. In the present investigation, pretreatment of animals with pentoxifylline inhibited lipopolysaccharide-induced serum tumor necrosis factor in a dose-dependent fashion. Pentoxifylline prevented the sequestration of neutrophils seen in animals given intravenous lipopolysaccharide. Furthermore, pentoxifylline protected animals from the lethal effects of an intravenous challenge with lipopolysaccharide. These data indicate that pentoxifylline inhibits lipopolysaccharide-induced tumor necrosis factor and may be an effective agent in mitigating the lethal consequences of sepsis and other disease processes mediated by this cytokine.

Tumor necrosis factor increases in vivo glucose utilization of macrophage-rich tissues

Glucose utilization of different tissues was investigated in vivo by the 2-deoxyglucose tracer technique. After infusion of a non-lethal dose of recombinant human TNF-alpha (150 micrograms/kg) to rats, glucose utilization was increased by 80-100% in spleen, liver, kidney, by 60% in skin and by 30-40% in lung and ileum. The largest increase (150%) was observed in the diaphragm. There was no significant change in glucose utilization by skeletal muscles, testis and brain. These data show that TNF exerts metabolic effects on macrophage-rich tissues, and suggest that enhanced secretion of TNF may be one of the important factors in eliciting the metabolic changes in sepsis and endotoxicosis.

Importance of TLR2 in Early Innate Immune Response to Acute Pulmonary Infection with Porphyromonas gingivalis in Mice

The periodontal pathogen Porphyromonas gingivalis is implicated in certain systemic diseases including atherosclerosis and aspiration pneumonia. This organism induces innate responses predominantly through TLR2, which also mediates its ability to induce experimental periodontitis and accelerate atherosclerosis. Using a validated mouse model of intratracheal challenge, we investigated the role of TLR2 in the control of P. gingivalis acute pulmonary infection. TLR2-deficient mice elicited reduced proinflammatory or antimicrobial responses (KC, MIP-1α, TNF-α, IL-6, IL-12p70, and NO) in the lung and exhibited impaired clearance of P. gingivalis compared with normal controls. However, the influx of polymorphonuclear leukocytes into the lung and the numbers of resident alveolar macrophages (AM) were comparable between the two groups. TLR2 signaling was important for in vitro killing of P. gingivalis by polymorphonuclear leukocytes or AM and, moreover, the AM bactericidal activity required NO production. Strikingly, AM were more potent than peritoneal or splenic macrophages in P. gingivalis killing, attributed to diminished AM expression of complement receptor-3 (CR3), which is exploited by P. gingivalis to promote its survival. The selective expression of CR3 by tissue macrophages and the requirement of TLR2 inside-out signaling for CR3 exploitation by P. gingivalis suggest that the role of TLR2 in host protection may be contextual. Thus, although TLR2 may mediate destructive effects, as seen in models of experimental periodontitis and atherosclerosis, we have now shown that the same receptor confers protection against P. gingivalis in acute lung infection.

Granulocyte Colony-Stimulating Factor Modulates the Pulmonary Host Response to Endotoxin in the Absence and Presence of Acute Ethanol Intoxication

Alcohol impairs neutrophil function and predisposes the host to infectious complications. Granulocyte colony-stimulating factor (G-CSF) increases both the number and functional activities of neutrophils. This study investigated the effects of G-CSF on the pulmonary response to endotoxin in rats with or without acute ethanol intoxication. Acute ethanol intoxication inhibited tumor necrosis factor (TNF)-alpha and macrophage inflammatory protein (MIP)-2 production in the lung and suppressed the recruitment of neutrophils into the lung. Ethanol also inhibited CD11b/c expression on recruited neutrophils and suppressed the phagocytic activity of circulating neutrophils. G-CSF pretreatment up-regulated CD11b/c expression on circulating polymorphonuclear leukocytes, augmented the recruitment of neutrophils into the lung, and enhanced the phagocytic activity of circulating and recruited neutrophils in both the absence and presence of acute ethanol intoxication. G-CSF inhibited MIP-2 but not TNF-alpha production in the lung. These data suggest that G-CSF may be useful in the prevention or treatment of infections in persons immunocompromised by alcohol.

Carbohydrate dynamics in the hypermetabolic septic rat

Glucose turnover is increased during shock and in acute sepsis, but relatively little information is available concerning the regulation of carbohydrate metabolism during the hypermetabolic phase of sepsis. In these studies peritoneal sepsis was induced in rats, following chronic vascular catheterization, by intraperitoneal administration of a pooled fecal inoculum. The resultant peritonitis has been shown to produce a sustained hypermetabolic state during the first three days of infection. Glucose and lactate kinetics were studied using a constant infusion of radiolabeled tracers during the peak of the hypermetabolic phase (day 2). The septic animals exhibited a 42% increase in glucose turnover and a 63% increase in the metabolic clearance rate of glucose, as compared to time-matched control rats. Hepatic glycogenolysis could only contribute 1% to 2% to the increased rate of glucose appearance. A major portion of the elevated glucose turnover was accounted for by a 93% increase in glucose recycling, indicating an enhancement of gluconeogenesis from glucose-derived gluconeogenic precursors. The increased importance of lactate as a precursor for gluconeogenesis in sepsis was indicated by the elevated lactate turnover (34%) and the increased percentage of 14C-glucose derived from 14C-lactate. The insulin to glucagon ratio was decreased in the septic animals as a result of a reduction in the plasma insulin concentration (56%) and an increased glucagon concentration (67%). We conclude that during the hypermetabolic phase of sepsis, the increased peripheral glucose uptake generated more gluconeogenic precursors but did not appear to have a major direct contribution to the increased aerobic metabolism.