EXPRESSION PATTERNS OF ADHESION RECEPTORS IN THE DEVELOPING MOUSE LUNG - FUNCTIONAL IMPLICATIONS

A detailed, immunohistological study of mouse lung development from th e first appearance of primary lung buds off the laryngo tracheal groov e through the formation of the mature, adult lung has been carried out using monoclonal antibodies specific for endothelial cells, smooth mu scle cells, adhesion receptors and markers of mature endothelial cell function. These included mAbs specific for PECAM-1, alpha-smooth muscl e actin, ICAM-1, lCAM-2, VCAM-1, alpha 4 and alpha 6 integrin subunits , thrombomodulin and factor VIII. The results document a dynamic patte rn of receptor expression and indicate that the expansion of the pulmo nary vascular system may take place by both angiogenic and vasculogeni c processes, They further document differences in receptor expression by vascular and airway smooth muscle. ICAM-1 expression was primarily extravascular during development. The expression patterns of alpha 4 i ntegrin and its counter receptor VCAM-1 lacked the complementarity tha t might be expected if they were functioning as a receptor/counter-rec eptor pair in lung development. Thrombomodulin expression patterns sup port a major role for the thrombin/thrombomodulin system in lung devel opment. The expression of thrombomodulin only at sites of airway branc hing suggests that the thrombin/thrombomodulin system could play a piv otal, regulatory role in branching morphogenesis.