IL-13 signaling via IL-13Rα 2 triggers TGF-β 1 -dependent allograft fibrosis

Background Allograft fibrosis still remains a critical problem in transplantation, including heart transplantation. The IL-13/TGF-β 1 interaction has previously been identified as a key pathway orchestrating fibrosis in different inflammatory immune disorders. Here we investigate if this pathway is also responsible for allograft fibrosis and if interference with the IL-13/TGF-β 1 interaction prevents allograft fibrosis. Methods FVB or control DBA/1 donor hearts were transplanted heterotopically into DBA/1 recipient mice and hearts were explanted at day 60 and 100 post-transplantation. Cardiac tissue was examined by Masson’s trichrome staining and immunohistochemistry for CD4, CD8, CD11b, IL-13, Fas ligand, matrix metalloproteinase (MMP)-1, MMP-13, β2-microglobulin, and Gremlin-1. Graft-infiltrating cells were isolated and analyzed by flow cytometry. IL-13 and TGF-β 1 levels were determined by enzyme-linked immunosorbent assay (ELISA) and the amount of collagen was quantified using a Sircol assay; IL-13Rα 2 expression was detected by Western blotting. In some experiments IL-13/ TGF-β 1 signaling was blocked with specific IL-13Rα 2 siRNA. Additionally, a PCR array of RNA isolated from the allografts was performed to analyze expression of multiple genes involved in fibrosis. Results Both groups survived long-term (>100 days). The allogeneic grafts were infiltrated by significantly increased numbers of CD4 + ( P <0.0001), CD8 + ( P <0.0001), and CD11b + cells ( P = 0.0065) by day 100. Furthermore, elevated IL-13 levels ( P = 0.0003) and numbers of infiltrating IL-13 + cells ( P = 0.0037), together with an expression of IL-13Rα 2 , were detected only within allografts. The expression of IL-13 and IL-13Rα 2 resulted in significantly increased TGF-β 1 levels ( P <0.0001), higher numbers of CD11b high Gr1 intermediate TGF-β 1 + cells, and elevated cardiac collagen deposition ( P = 0.0094). The allograft fibrosis found in these experiments was accompanied by upregulation of multiple profibrotic genes, which was confirmed by immunohistochemical stainings of allograft tissue. Blockage of the IL-13/TGF-β 1 interaction by IL-13Rα 2 siRNA led to lower numbers of CD11b high Gr1 intermediate TGF-β 1 + , CD4 + , CD8 + , and CD11b + cells, and prevented collagen deposition ( P = 0.0018) within these allografts. Conclusions IL-13 signaling via IL-13Rα 2 induces TGF-β 1 and causes allograft fibrosis in a murine model of chronic transplant rejection. Blockage of this IL-13/TGF-β 1 interaction by IL-13Rα 2 siRNA prevents cardiac allograft fibrosis. Thus, IL-13Rα 2 may be exploitable as a future target to reduce allograft fibrosis in organ transplantation.