LUNG INTERLEUKIN-5 EXPRESSION IN MURINE BLEOMYCIN-INDUCED PULMONARY FIBROSIS

Eosinophils are primary sources of fibrogenic cytokines in lung fibros is, and interleukin (IL)-5 is important in their differentiation, prol iferation, recruitment and activation. To investigate the potential ro le of this cytokine, lung IL-5 expression was examined in a murine mod el of bleomycin-induced pulmonary fibrosis. Analysis of lung RNA showe d significant increases in lung IL-5 mRNA content between days 3 and 1 4 after induction of lung injury, which decreased toward control level s after day 21. In situ hybridization revealed essentially no detectab le IL-5 mRNA expression before day 3, but showed elevated expression i n mononuclear cells and eosinophils between days 3 and 14, localized w ithin areas of active fibrosis. After 21 days, the intensity and numbe r of IL-5 expressing cells significantly declined. Immunostaining with anti-IL-5 antibodies confirmed the predominant IL-5 expression by mon onuclear cells and eosinophils in areas of active fibrosis. The kineti cs of increase in the number of cells expressing significant IL-5 mRNA in lung sections paralleled that for IL-5 mRNA expression in whole-lu ng homogenates. These results demonstrate for the first time that IL-5 is upregulated in this murine model and suggest a novel role for this cytokine in pulmonary fibrosis via its ability to recruit and activat e eosinophils.