In several allergic, autoimmune, and
infectious diseases,
fibrosis is a major cause of morbidity and mortality. Here, using a model of
infection-induced
liver fibrosis, we show that
interleukin (IL)-13 is required at all stages of
Schistosomiasis mansoni infection to induce
fibrosis.
IL-4 production was preserved in IL-13-deficient mice, yet failed to significantly contribute to the fibrotic response in either acute or
chronic infection. Significant
fibrosis develops in all infected mice, although the magnitude of the response varies widely in inbred mice. C3H/HeN, BALB/c, and C57BL/6 mice develop high, intermediate, and low levels of
fibrosis, respectively. Despite these differences,
IL-13 antagonism resulted in a marked amelioration of
fibrosis in all strains. The fibrotic mechanism in the high- and low-responder strains was unrelated to their tissue eosinophil or mast cell responses, but did correlate with their patterns of
IL-13,
IL-10, and
interferon gamma (IFN-gamma)
mRNA expression. Indeed, severe
fibrosis correlated with a high
IL-13 and low IFN-gamma/IL-10
mRNA response. Because fibrotic diseases are typically progressive disorders, an important issue was to determine whether
IL-13 inactivation might be used to treat an established and ongoing fibrotic disease. Here,
IL-13 antagonism was highly efficacious, even after
fibrosis and the Th2
cytokine response were firmly established. These studies demonstrate the central role played by
IL-13 in fibrogenesis and suggest that therapeutic approaches aimed at disrupting the
IL-13 pathway will be highly effective at preventing fibrotic disease caused by chronic Th2-mediated inflammatory reactions.