Lung TGF-β1 in WT and IL-5–deficient mice repetitively challenged with OVA. (a) WT mice challenged with OVA developed increased levels of lung TGF-β1 compared with non–OVA-challenged WT mice (*WT OVA versus WT no OVA; P < 0.01). Significantly reduced levels of TGF-β1 were detected in IL-5–deficient mice versus WT mice challenged with OVA (**IL-5 KO OVA versus WT OVA; P < 0.05). (b) WT mice challenged with OVA had a significant increase in the number of peribronchial MBP-positive cells (^#WT OVA versus WT no OVA; P < 0.001) and TGF-β–positive cells (^†WT OVA versus WT no OVA; P < 0.001). There was a significant reduction in the number of MBP-positive cells (^##IL-5 KO OVA versus WT OVA; P < 0.001) and TGF-β–positive cells (^††IL-5 KO OVA versus WT OVA; P < 0.001) in IL-5–deficient mice challenged with OVA. (c–j) Non–OVA-challenged WT mice had few cells that immunostained positive for MBP (c) or TGF-β (d). OVA-challenged WT mice had a significant increase in the number of cells that immunostain positive for MBP (e) or TGF-β (f). OVA challenged IL-5–deficient mice had few cells that immunostained positive for MBP (i) or TGF-β (j). Epithelial cells in OVA-challenged IL-5–deficient mice did immunostain positive for TGF-β (j). Non–OVA-challenged IL-5–deficient mice had few cells that immunostained positive for MBP (g) or TGF-β (h). The arrows in k point to three of four MBP-positive cells. The arrows in l point to three cells that are TGF-β1 positive (corresponding to the same three MBP-positive cells in k). Several additional TGF-β1–positive cells that do not correspond to MBP-positive cells are also noted in l.