Vascular expression of the avb3-integrin in lung and other organs

Singh, Baljit, Chenzhong Fu, and Jahar Bhattacharya. Vascular expression of the avb3-integrin in lung and other organs. Am. J. Physiol. Lung Cell. Mol. Physiol. 278: L217–L226, 2000.—The expression of the avb3-integrin in nonproliferating vascular beds remains unclear. To determine possible organ-specific differences, we compared avb3integrin expression in the lung and other organs. Paraffinembedded tissue sections of lung, liver, brain, muscle and skin obtained from rats were processed for immunohistochemistry with a monoclonal (LM609) and a polyclonal antibody (AB1903) against the avb3-integrin. Immunogold electron microscopy was used to localize avb3-integrin in rat lung microvasculature. With the use of custom-designed primers, lung sections were subjected to in situ PCR in a thermal cycler to amplify av or b3 mRNA. To confirm specific amplification, PCR products were further hybridized in situ with an av or b3 cDNA probe. In the lung, the avb3-integrin protein as well as av and b3 mRNAs was extensively evident in the endothelium of extra-alveolar and alveolar microvessels, in vascular smooth muscle, and in large bronchial epithelium but not in the epithelium of alveolar ducts or alveoli. Ultrastructural immunogold labeling showed the presence of the integrin on the luminal and abluminal faces of the lung microvascular endothelium but not on the apical surface of the alveolar epithelium. Staining for the integrin was generally negative in blood vessels of several systemic organs, although weak staining was evident in branches of the hepatic portal vein. The constitutive presence of the av and b3 mRNAs and the avb3-integrin in the lung microvascular bed suggests that gene transcription for the integrin is ongoing in lung vessels. Because it binds vitronectin, the lung vascular avb3-integrin may play a role in ligation of bloodborne, vitronectin-containing macromolecular complexes formed in inflammation.