Widespread codistribution of glycoprotein gp 115 and elastin in chick eye and other tissues

Frozen sections of chick tissues were exposed to affinity-purified monoclonal antibodies raised against chick gp 115 and to affinity-purified antibodies raised against chick tropoelastin to study the distribution pattern of the corresponding antigens by the avidin-biotin immunoperoxidase technique. Laminin and fibronectin antibodies were used for comparison. Gp 115 and tropoelastin antibodies localized to the same structure in several of the tissues examined. The endothelial membrane of the cornea and Bruch's membrane in the choroid were positive, while the corneal epithelial membrane was negative. Both antibodies displayed a peculiar punctate reactivity in the corneal stroma and a very fine fibrillar pattern in the conjunctiva and at the corneal-scleral junction. Liver, heart and large vessels, striated muscle and skin showed a similar pattern both for tropoelastin and gp 115 antibodies. Few differences were seen in the distribution of the reactivity: the pericellular matrix of intestinal smooth muscle cells was stained by gp 115 but not by tropoelastin antibodies. However, the reactivity of gp 115 and tropoelastin antibodies was similarly distributed in the lung smooth muscle cell clusters. The peritubular matrix in the kidney did also not react with tropoelastin antibodies as did the brain intraparenchymal vessels; whereas gp 115 antibody reactivity was present in both sites. We interpret these lack of apparent codistribution in some tissues as a variation in the relative availability of the target antigen for the reaction with the antibody and not as a consequence of a qualitative difference in the distribution of gp 115 and tropoelastin. By the use of anti gp 115 monoclonal antibodies that do not cross-react, and presumably recognize different epitopes, it was shown that some but not all antibodies, react with brain intraparenchymal blood vessels; whereas the pattern of distribution in other tissues was the same. This suggests that in vessels with an undetectable level of elastin, certain epitopes of gp 115 molecule might not be recognized as a result of being masked by other components or by a different conformation of the molecule.