Hookworm infection among school age children in Kintampo north municipality, Ghana: nutritional risk factors and response to albendazole treatment.

Children (n = 812) 6-11 years of age attending 16 schools in the Kintampo North Municipality of Ghana were screened for participation in a study on hookworm infection, nutrition, and response to albendazole. The prevalence of Necator americanus hookworm infection (n = 286) was 39.1%, and significant predictors of infection included age, malaria parasitemia, lack of health care, school area, levels of antibodies against hookworm, and low consumption of animal foods. The cure rate after a single dose (400 mg) albendazole was 43%, and the mean fecal egg count reduction rate was 87.3%. Data for an in vitro egg hatch assay showed a trend toward reduced albendazole susceptibility in post-treatment hookworm isolates (P = 0.06). In summary, hookworm infection is prevalent among school age children in the Kintampo North Municipality and animal food intake inversely correlates with infection status. Modest cure rates and fecal egg count reduction rates reinforce the need for further investigation of potential benzimidazole resistance in Ghana.

Frequency and intensity of exposure mediate resistance to experimental infection with the hookworm, Ancylostoma ceylanicum.

Hookworms are bloodfeeding intestinal nematodes that are a major cause of anemia in resource-limited countries. Despite repeated exposure beginning in early childhood, humans retain lifelong susceptibility to infection without evidence of sterilizing immunity. In contrast, experimental infection of laboratory animals is typically characterized by varying degrees of resistance following primary infection, although the mechanisms underlying this phenomenon remain unknown. In this study, hamsters subjected to a single drug-terminated infection with 100 third stage hookworm larvae were confirmed to be resistant to pathological effects following a subsequent challenge. In a second experiment, hamsters infected twice-weekly with 10 third stage larvae (low inoculum) exhibited clinical and parasitological evidence of continued susceptibility, while those given 100 L3 (high inoculum) developed apparent resistance within 3 days following the initial exposure. The kinetics of parasite-specific IgA, IgM, and IgG antibody production varied by group, which suggests that the humoral immune response to hookworm infection is stimulated by the nature (frequency and intensity) of larval exposure. These results suggest that intermittent low-inoculum larval exposure, which is characterized by prolonged susceptibility to infection, may serve as a more representative model of human hookworm disease for studies of pathogenesis, as well as drug and vaccine development.

Alveolar epithelial STAT3, IL-6 family cytokines, and host defense during Escherichia coli pneumonia.

While signal transducer and activator of transcription (STAT) 3 signaling has been linked to multiple pathways influencing immune function and cell survival, the direct influence of this transcription factor on innate immunity and tissue homeostasis during pneumonia is unknown. Human patients with dominant-negative mutations in the Stat3 gene develop recurrent pneumonias, suggesting a role for STAT3 in pulmonary host defense. We hypothesized that alveolar epithelial STAT3 is activated by IL-6 family cytokines and is required for effective responses during gram-negative bacterial pneumonia. STAT3 phosphorylation was increased in pneumonic mouse lungs and in murine lung epithelial (MLE)-15 cells stimulated with pneumonic bronchoalveolar lavage fluid (BALF) through 48 hours of Escherichia coli pneumonia. Mice lacking active STAT3 in alveolar epithelial cells (Stat3(Delta/Delta)) had fewer alveolar neutrophils and more viable bacteria than control mice early after intratracheal E. coli. By 48 hours after E. coli infection, however, lung injury was increased in Stat3(Delta/Delta) mice. Bacteria were cleared from lungs of both genotypes, albeit more slowly in Stat3(Delta/Delta) mice. Of the IL-6 family cytokines measured in lungs from infected C57BL/6 mice, IL-6, oncostatin M, leukemia inhibitory factor (LIF), and IL-11 were significantly elevated. Neutralization studies demonstrated that LIF and IL-6 mediated BALF-induced STAT3 activation in MLE-15 cells. Together, these results indicate that during E. coli pneumonia, select IL-6 family members activate alveolar epithelial STAT3, which functions to promote neutrophil recruitment and to limit both infection and lung injury.

Tumor suppressor PTEN is a physiologic suppressor of chemoattractant-mediated neutrophil functions.

The recruitment and activation of neutrophils at infected tissues is essential for host defense against invading microorganisms. However, excessive neutrophil recruitment or activation can also damage the surrounding tissues and cause unwanted inflammation. Hence, the responsiveness of neutrophils needs to be tightly regulated. In this study, we have investigated the functional role of tumor suppressor PTEN in neutrophils by using a mouse line in which PTEN is disrupted only in myeloid-derived cells. Chemoattractant-stimulated PTEN(-/-) neutrophils displayed significantly higher Akt phosphorylation and actin polymerization. A larger fraction of these neutrophils displayed membrane ruffles in response to chemoattractant stimulation. In addition, chemoattractant-induced transwell migration and superoxide production were also augmented. Single-cell chemotaxis assays showed that PTEN(-/-) neutrophils have a small (yet statistically significant) defect in directionality. However, these neutrophils also showed an increase in cell speed. As a result, overall chemotaxis, which depends on speed and directionality, was not affected. Consistent with the increased responsiveness of PTEN(-/-) neutrophils, the in vivo recruitment of these cells to the inflamed peritoneal cavity was significantly enhanced. Thus, as a physiologic-negative regulator, PTEN should be a promising therapeutic target for modulating neutrophil functions in various infectious and inflammatory diseases.

Functions and regulation of NF-kappaB RelA during pneumococcal pneumonia.

Eradication of bacteria in the lower respiratory tract depends on the coordinated expression of proinflammatory cytokines and consequent neutrophilic inflammation. To determine the roles of the NF-kappaB subunit RelA in facilitating these events, we infected RelA-deficient mice (generated on a TNFR1-deficient background) with Streptococcus pneumoniae. RelA deficiency decreased cytokine expression, alveolar neutrophil emigration, and lung bacterial killing. S. pneumoniae killing was also diminished in the lungs of mice expressing a dominant-negative form of IkappaBalpha in airway epithelial cells, implicating this cell type as an important locus of NF-kappaB activation during pneumonia. To study mechanisms of epithelial RelA activation, we stimulated a murine alveolar epithelial cell line (MLE-15) with bronchoalveolar lavage fluid (BALF) harvested from mice infected with S. pneumoniae. Pneumonic BALF, but not S. pneumoniae, induced degradation of IkappaBalpha and IkappaBbeta and rapid nuclear accumulation of RelA. Moreover, BALF-induced RelA activity was completely abolished following combined but not individual neutralization of TNF and IL-1 signaling, suggesting either cytokine is sufficient and necessary for alveolar epithelial RelA activation during pneumonia. Our results demonstrate that RelA is essential for the host defense response to pneumococcus in the lungs and that RelA in airway epithelial cells is primarily activated by TNF and IL-1.

Vascular endothelial growth factor is an important determinant of sepsis morbidity and mortality.

Sepsis, the systemic inflammatory response to infection, is a leading cause of morbidity and mortality. The mechanisms of sepsis pathophysiology remain obscure but are likely to involve a complex interplay between mediators of the inflammatory and coagulation pathways. An improved understanding of these mechanisms should provide an important foundation for developing novel therapies. In this study, we show that sepsis is associated with a time-dependent increase in circulating levels of vascular endothelial growth factor (VEGF) and placental growth factor (PlGF) in animal and human models of sepsis. Adenovirus-mediated overexpression of soluble Flt-1 (sFlt-1) in a mouse model of endotoxemia attenuated the rise in VEGF and PlGF levels and blocked the effect of endotoxemia on cardiac function, vascular permeability, and mortality. Similarly, in a cecal ligation puncture (CLP) model, adenovirus-sFlt-1 protected against cardiac dysfunction and mortality. When administered in a therapeutic regimen beginning 1 h after the onset of endotoxemia or CLP, sFlt peptide resulted in marked improvement in cardiac physiology and survival. Systemic administration of antibodies against the transmembrane receptor Flk-1 but not Flt-1 protected against sepsis mortality. Adenovirus-mediated overexpression of VEGF but not PlGF exacerbated the lipopolysaccharide-mediated toxic effects. Together, these data support a pathophysiological role for VEGF in mediating the sepsis phenotype.

Roles of interleukin-6 in activation of STAT proteins and recruitment of neutrophils during Escherichia coli pneumonia.

Interleukin (IL)-6 concentrations are positively associated with the severity of pneumonia, and this cytokine is essential to surviving experimental pneumococcal pneumonia. The role that IL-6 plays during pneumonia and its impact during gram-negative bacterial pneumonia remain to be determined. During Escherichia coli pneumonia, IL-6-deficient mice had increased bacterial burdens in their lungs, indicating compromised host defenses. Decreased neutrophil counts in alveolar air spaces, despite normal blood neutrophil counts and survival of emigrated neutrophils, suggested that defective neutrophil recruitment was responsible for exacerbating the infection. Neutrophil recruitment requires nuclear factor (NF)- kappa B, but IL-6 was neither sufficient nor essential to induce NF- kappa B-mediated gene expression in the lungs. In contrast, IL-6 induced the phosphorylation of signal transducer and activator of transcription (STAT) 1 and STAT3 in the lungs, and STAT1 and STAT3 phosphorylation during E. coli pneumonia was decreased by IL-6 deficiency. Thus, IL-6 plays essential roles in activating STAT transcription factors, enhancing neutrophil recruitment, and decreasing bacterial burdens during E. coli pneumonia.

Lung NF-kappaB activation and neutrophil recruitment require IL-1 and TNF receptor signaling during pneumococcal pneumonia.

Pulmonary inflammation is an essential component of the host defense against Streptococcus pneumoniae infection of the lungs. The early response cytokines, TNF-alpha and IL-1, are rapidly induced upon microbial exposure. Mice deficient in all TNF- and IL-1-dependent signaling receptors were used to determine the roles of these cytokines during pneumococcal pneumonia. The deficiency of signaling receptors for TNF and IL-1 decreased bacterial clearance. Neutrophil recruitment to alveolar air spaces was impaired by receptor deficiency, as was pulmonary expression of the neutrophil chemokines KC and MIP-2. Because NF-kappaB mediates the expression of both chemokines, we assessed NF-kappaB activation in the lungs. During pneumococcal pneumonia, NF-kappaB proteins translocate to the nucleus and activate gene expression; these functions were largely abrogated by the deficiency of receptors for TNF-alpha and IL-1. Thus, the combined deficiency of TNF and IL-1 signaling reduces innate immune responses to S. pneumoniae in the lungs, probably due to essential roles for these receptors in activating NF-kappaB.