Lungs of P0 Clec1b^−/− and Syk^−/− mice have a similar pathology. (A) Representative low magnification (10×) photomicrographs of H&E-stained paraffin sections from P0 lung showed detail of the lung's contribution to the lethal phenotype of the Clec1b^−/− and Syk^−/− mice (n ≥ 3 for each genotype). Lungs from P0 wild-type (+/+) mice showed large open bronchi and expanded terminal air sacs with thin septae between airspaces. In contrast, lungs from Clec1b^−/− and Syk^−/− mice showed fluid accumulation in the bronchi (black arrows) as well as incompletely expanded terminal airways. Scale bar = 100 μm. (B) Lymphatic vessels (LVs) localized next to blood vessels (BVs) were identified with an Ab to podoplanin (brown staining). These vessels were clear in Clec1b^+/+ and Syk^+/+ (+/+) mice but contained red blood cells in Clec1b^−/− and Syk^−/− mice, indicating a connection between the lymphatic and circulatory systems. Scale bar = 20 μm.