An Enhanced Expression Of The Decoy Receptor IL-13Rα2 In Macrophages And Its Effects On Immunopathogenesis Of Schistosomiasis Japonica

Interleukin (IL)-13 and IL-13 receptor (R)α2 appear to play a major role in tissue fibrosis of schistosomiasis and asthma. IL-13 is produced by T helper 2 (Th2) cells. The two binding receptor chains for IL-13 include IL-13Rα1 and IL-13Rα2. When expressed alone, IL-13Rα1 binds IL-13 with low affinity. However, when IL-13Rα1 is coexpressed with IL-4Rα, a high-affinity heterodimerized receptor is formed, regulating the biological activity of IL-13. In contrast, IL-13Rα2, an essential component for binding and internalization of IL-13 but not for IL-13-induced signal transduction, binds IL-13 with high affinity and is known as the decoy receptor. IL-13Rα2 or sIL-13Rα2-Fc fusion protein is highly inhibition of IL-13 activity. To target IL-13 receptor-positive tumor cells, a recombinant fusion IL-13 cytotoxin termed IL-13-PE38QQR or IL-13-PE was developed. It has been shown that IL-13 cytotoxin induces apoptotic cell death in tumor cells. IL-13Rα2 chain is targeted with a receptor-directed cytotoxin of IL-13-PE to induce specific killing in cancer cells. Based on these experimental results, clinical trials of IL-13Rα2 cancer therapy have been initiated.IL-13 is a key regulator of the extracellular matrix. It stimulates collagen production in fibroblasts. Its effects on fibrosis are direct with no effect on granuloma size. Elucidating the mechanisms leading to pathology and fibrosis may lead to more effective strategies for immunological intervention in a variety of chronic diseases. Biological activity and regulation of production and function of IL-13 have become an intensive area of research.IL-13 also plays an important role in schistosomiasis pathogenesis. Serum levels of IL-13Rα2 in both human and mice were upregulated in Schistosoma mansoni (S. mansoni). IL-13Rα2-deficient mice (IL-13Rα2-/-) had a marked exacerbation in hepatic fibrosis. Pathology was prevented when IL-13Rα2-deficient mice were treated with a soluble IL-13Rα2-Fc construct, demonstrating that their exacerbated fibrotic response was due to increased IL-13 activity. IL-13Rα2 down-modulates granulomatous inflammation and prolongs host survival in schistosomiasis. However, much less is known about IL-13Rα2 in S. japonicum, particularly given the difference in the pathology of S. mansoni and S. japonicum. Because Th2 cytokines must bind to their receptors to induce biological responses, the responding cells of IL-13 and the functional activity of IL-13 are unclear. The aim of the present study is to determine in S. japonicum-infected mice: (1) whether the expression of IL-13Rα2 is inducible in a manner similar to that described in S. mansoni studies, and (2) the expression of IL-13Rα2 in macrophages and its effects on immunopathogenesis of schistosomiasis.The main contents are divided into two sections, as follows:1. Enhanced expression of IL-13Rα2 mRNA and protein in S. japonicum miceWe exposed a large number of mice to cercariae and established S. japonicum mouse model. Serum levels of IL-13Rα2 at 6,8,and 12 weeks postinfection were examined with ELISA. Using the Primer Express Software v5.0 with mouse IL-13Rα2 sequence obtained from GenBank (Accession number NM008356), PCR primers were designed and synthesized. IL-13Rα2 mRNA and protein in liver tissues were determined by RT-PCR and immunoblotting analysis, respectively. Result: ELISA revealed that serum levels of soluble IL-13Rα2 were significantly elevated at all time points after infection. The peak levels were at 6 weeks postinfection. 800 bp of IL-13Rα2 cDNA was amplified in whole liver tissues from the infected mice. A specific band of IL-13Rα2 protein between 35-49 KD was detected in the same samples. Hence, the decoy receptor (IL-13Rα2) mRNA and protein in S. japonicum mice were elevated.2. Enhanced expression of IL-13Rα2 in macrophages and its effects in immunopathogenesis of schistosomiasis1) Identification of IL-13Rα2 expression in macrophages in vitroPeritoneal macrophages of infected mice (8 weeks postinfection) or uninfected mice were isolated. RNA was extracted and analyzed using TaqMan PCR. IL-13Rα2 expression in macrophages was performed by the double-labelled fluorescent immunocytochemistry technique with primary antibody of goat anti-mouse IL-13Rα2 antibody and monoclonal anti-CD68 antibody, ED1. The results showed that the level of IL-13Rα2 mRNA was markedly (6-fold) enhanced in infected mice compared to that in uninfected mice. In addition, collagen ? gene was 2.5-fold higher in infected mice relative to healthy controls. As indicated by immunocytochemical staining, IL-13Rα2 was expressed in ED1 positive macrophages. These experiments confirmed the production of IL-13Rα2 by ED1 positive macrophages in schistosomiasis. Hence an enhanced expression of IL-13Rα2 was further demonstrated in primary macrophages of murine schistosomiasis.2) Inactivation of IL-13Rα2 expressing macrophages down-modulates granulomatous inflammation in vivoWe treated mice of schistosomiasis with GdCl3, a reported macrophage depletion reagent. A macrophage-inactivated S. japonicum-infected mouse model was successfully established. Whole liver from each mouse was prepared following perfusion of blood with PBS at 42 days postinfection. Tristain immunofluorescence and TaqMan PCR were used to detect the coexpression of IL-13Rα2 and the macrophage marker (ED1) in liver tissues. These experiments confirmed specifically enhanced expression of IL-13Rα2 in the macrophages of schistosomiasis. Inactivation of IL-13Rα2 expressing macrophages accordingly down-modulates granulomatous inflammation and inhibits fibrosis. Our major findings are summarized below:Expression of the decoy receptor IL-13Rα2 in S. japonicum mice was increased. Specifically enhanced expression of IL-13Rα2 in macrophages of schistosomiasis was confirmed. Inactivation of IL-13Rα2 expressing macrophages down-modulates granulomatous inflammation and inhibits fibrosis. Hence IL-13Rα2 expressed in macrophages may be a critical contributor to the immunopathogenesis of schistosomiasis. Our data highlight the potential importance of IL-13 signaling and antifibrotic therapeutics in Th2-mediated immune diseases.