Th2 CD4+ T Cells Are Necessary and Sufficient for Schistosoma-Pulmonary Hypertension.

Background Inflammation underlies many forms of pulmonary hypertension (PH), including that resulting from Schistosoma infection, a major cause of PH worldwide. Schistosomiasis-associated PH is proximately triggered by embolization of parasite eggs into the lungs, resulting in localized type 2 inflammation. However, the role of CD4+ T cells in this disease is not well defined. Methods and Results We used a mouse model of schistosomiasis-associated PH, induced by intraperitoneal egg sensitization followed by intravenous egg challenge, with outcomes including right ventricle systolic pressure measured by cardiac catheterization, and cell density and phenotype assessed by flow cytometry. We identified that embolization of Schistosoma eggs into lungs of egg-sensitized mice increased the perivascular density of T-helper 2 (Th2) CD4+ T cells by recruitment of cells from the circulation and triggered type 2 inflammation. Parabiosis confirmed that egg embolization is required for localized type 2 immunity. We found Th2 CD4+ T cells were necessary for Schistosoma-induced PH, given that deletion of CD4+ T cells or inhibiting their Th2 function protected against type 2 inflammation and PH following Schistosoma exposure. We also observed that adoptive transfer of Schistosoma-sensitized CD4+ Th2 cells was sufficient to drive type 2 inflammation and PH. Conclusions Th2 CD4+ T cells are a necessary and sufficient component for the type 2 inflammation-induced PH following Schistosoma exposure.

Paclitaxel blocks Th2-mediated TGF-ß activation in Schistosoma mansoni-induced pulmonary hypertension.

Schistosomiasis is a leading cause of pulmonary hypertension (PH) worldwide. Recent studies reveal that the type-2 immune cytokines IL-4 and IL-13, as well as consequent activation of TGF-ß, are key factors in the pathogenesis of Schistosoma-PH. Paclitaxel has been reported to act as an adjuvant for Th2 inflammation while downregulating TGF-ß activation. Moreover, paclitaxel blocks PH in monocrotaline and SU5416-hypoxia models. We hypothesized that paclitaxel would augment Th2 inflammation while blocking TGF-ß activation and PH after schistosomiasis exposure. Wild-type mice (C57BL6/J; 6/group) were intraperitoneally (IP) sensitized and then intravenously (IV) challenged with Schistosoma mansoni eggs. One day after IV egg challenge, the mice were treated with a single IP dose of 25 mg/kg paclitaxel or vehicle. Right ventricular (RV) catheterization was performed and granuloma volumes and vascular remodeling were quantified. Lung cytokines were quantified by ELISA and reverse transcription polymerase chain reaction, and the quantity of active TGF-ß was determined using a cell reporter line. We also investigated hypoxia-induced PH. Paclitaxel treatment significantly protected mice from Schistosoma-PH, with decreased RV systolic pressure ( P = 0.005) and pulmonary vascular media thickness. Inflammation was significantly suppressed, contrary to our hypothesis, with decreased IL-4 and IL-13 levels, smaller granulomas, and less active TGF-ß following paclitaxel treatment. There was no change in IFN-γ or FoxO1 or FoxO3 expression. Paclitaxel did not suppress chronic hypoxia-induced PH, which is also TGF-ß-driven but independent of type-2 immunity. Paclitaxel protects against Schistosoma-induced PH in mice, although by blocking proximate Th2 inflammation rather than suppressing distal TGF-ß activation.

Vascular Adaptation of the Right Ventricle in Experimental Pulmonary Hypertension.

Optimal right ventricular (RV) function in pulmonary hypertension (PH) requires structural and functional coupling between the RV cardiomyocyte and its adjacent capillary network. Prior investigations have indicated that RV vascular rarefaction occurs in PH, which could contribute to RV failure by reduced delivery of oxygen or other metabolic substrates. However, it has not been determined if rarefaction results from relative underproliferation in the setting of tissue hypertrophy or from actual loss of vessels. It is also unknown if rarefaction results in inadequate substrate delivery to the RV tissue. In the present study, PH was induced in rats by SU5416-hypoxia-normoxia exposure. The vasculature in the RV free wall was assessed using stereology. Steady-state metabolomics of the RV tissue was performed by mass spectrometry. Complementary studies were performed in hypoxia-exposed mice and rats. Rats with severe PH had evidence of RV failure by decreased cardiac output and systemic hypotension. By stereology, there was significant RV hypertrophy and increased total vascular length in the RV free wall in close proportion, with evidence of vessel proliferation but no evidence of endothelial cell apoptosis. There was a modest increase in the radius of tissue served per vessel, with decreased arterial delivery of metabolic substrates. Metabolomics revealed major metabolic alterations and metabolic reprogramming; however, metabolic substrate delivery was functionally preserved, without evidence of either tissue hypoxia or depletion of key metabolic substrates. Hypoxia-treated rats and mice had similar but milder alterations. There is significant homeostatic vascular adaptation in the right ventricle of rodents with PH.

Role of vascular endothelial growth factor signaling in Schistosoma-induced experimental pulmonary hypertension.

There is significant evidence that Th2 (T helper 2)-mediated inflammation supports the pathogenesis of both human and experimental animal models of pulmonary hypertension (PH). A key immune regulator is vascular endothelial growth factor (VEGF), which is produced by Th2 inflammation and can itself contribute to Th2 pulmonary responses. In this study, we interrogated the role of VEGF signaling in a murine model of schistosomiasis-induced PH with a phenotype of significant intrapulmonary Th2 inflammation, vascular remodeling, and elevated right ventricular pressures. We found that VEGF receptor blockade partially suppressed the levels of the Th2 inflammatory cytokines interleukin (IL)-4 and IL-13 in both the lung and the liver after Schistosoma mansoni exposure and suppressed pulmonary vascular remodeling. These findings suggest that VEGF positively contributes to schistosomiasis-induced vascular inflammation and remodeling, and they also provide evidence for a VEGF-dependent signaling pathway necessary for pulmonary vascular remodeling and inflammation in this model.

The pulmonary endothelial glycocalyx regulates neutrophil adhesion and lung injury during experimental sepsis.

Sepsis, a systemic inflammatory response to infection, commonly progresses to acute lung injury (ALI), an inflammatory lung disease with high morbidity. We postulated that sepsis-associated ALI is initiated by degradation of the pulmonary endothelial glycocalyx, leading to neutrophil adherence and inflammation. Using intravital microscopy, we found that endotoxemia in mice rapidly induced pulmonary microvascular glycocalyx degradation via tumor necrosis factor-α (TNF-α)-dependent mechanisms. Glycocalyx degradation involved the specific loss of heparan sulfate and coincided with activation of endothelial heparanase, a TNF-α-responsive, heparan sulfate-specific glucuronidase. Glycocalyx degradation increased the availability of endothelial surface adhesion molecules to circulating microspheres and contributed to neutrophil adhesion. Heparanase inhibition prevented endotoxemia-associated glycocalyx loss and neutrophil adhesion and, accordingly, attenuated sepsis-induced ALI and mortality in mice. These findings are potentially relevant to human disease, as sepsis-associated respiratory failure in humans was associated with higher plasma heparan sulfate degradation activity; moreover, heparanase content was higher in human lung biopsies showing diffuse alveolar damage than in normal human lung tissue.