In schistosomiasis, the pathology resulting from chronic infection is predominantly induced by the host immune response to parasite eggs that are laid, in the case of Schistosoma mansoni, in the portal venous system and subsequently trapped in the liver and intestine. The egg induced granulomatous response eventually triggers significant liver fibrosis, which is the primary cause of chronic morbidity and mortality. Consequently, much of our current work is focused on elucidating the mechanisms of granulomatous inflammation and fibrosis. Progress was made in the following areas: 1) The mechanisms underlying schistosomiasis-induced pulmonary hypertension (PH), one of the most common causes of PH worldwide, remain unclear. We sought to determine whether Schistosoma mansoni causes experimental PH associated with pulmonary vascular remodeling in an interleukin (IL)-13-dependent manner. IL-13Ralpha1 is the canonical IL-13 signaling receptor, whereas IL-13Ralpha2 is a competitive nonsignaling decoy receptor. Wild-type, IL-13Ralpha1(-/-), and IL-13Ralpha2(-/-) C57BL/6J mice were percutaneously infected with S. mansoni cercariae, followed by i.v. injection of eggs. We assessed PH with right ventricular catheterization, histological evaluation of pulmonary vascular remodeling, and detection of IL-13 and transforming growth factor-beta signaling. Infected mice developed pulmonary peri-egg granulomas and arterial remodeling involving predominantly the vascular media. In addition, gain-of-function IL-13Ralpha2(-/-) mice had exacerbated vascular remodeling and PH. Mice with loss of IL-13Ralpha1 function did not develop PH and had reduced pulmonary vascular remodeling. Moreover, the expression of resistin-like molecule-alpha, a target of IL-13 signaling, was increased in infected wild-type and IL-13Ralpha2(-/-) but not IL-13Ralpha1(-/-) mice. Phosphorylated Smad2/3, a target of transforming growth factor-beta signaling, was increased in both infected mice and humans with the disease. Our data indicate that experimental schistosomiasis causes PH and potentially relies on up-regulated IL-13 signaling. 2) IL-22 is a member of the IL-10 cytokine family and signals through a heterodimeric receptor composed of the common IL-10R2 subunit and the IL-22R subunit. IL-10 and IL-22 both activate the STAT3 signaling pathway;however, in contrast to IL-10, relatively little is known about IL-22 in the host response to infection. In this study, using IL-22(-/-) mice, neutralizing Abs to IL-22, or both, we show that IL-22 is dispensable for the development of immunity to the opportunistic pathogens Toxoplasma gondii and Mycobacterium avium when administered via the i.p. or i.v. route, respectively. IL-22 also played little to no role in aerosol infections with Mycobacterium tuberculosis and in granuloma formation and hepatic fibrosis following chronic percutaneous infections with the helminth parasite Schistosoma mansoni. A marked pathogenic role for IL-22 was, however, identified in toxoplasmosis when infections were established by the natural oral route. Anti-IL-22 Ab-treated mice developed significantly less intestinal pathology than control Ab-treated mice even though both groups displayed similar parasite burdens. The decreased gut pathology was associated with reduced IL-17A, IL-17F, TNF-alpha, and IFN-gamma expression. In contrast to the prior observations of IL-22 protective effects in the gut, these distinct findings with oral T. gondii infection demonstrate that IL-22 also has the potential to contribute to pathogenic inflammation in the intestine. The IL-22 pathway has emerged as a possible target for control of inflammation in certain autoimmune diseases. Our findings suggest that few if any infectious complications would be expected with the suppression of IL-22 signaling.
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