Confocal microscopic analysis of integrin expression on the microvasculature and its sprouts in the neonatal foreskin.

Members of the integrin family of adhesion receptors are essential participants in blood vessel growth and remodeling. It is not known which integrins are involved in the initial stages of angiogenesis in vivo. In this study we determined the location of integrins on the blood vessels of a growing tissue, the neonatal foreskin, in which neovascularization is likely to occur. We used the confocal microscope to visually reconstruct vessels from the papillary dermis of the foreskin and to identify potential sprouts as narrow, tapering extensions from these vessels. Blood vessels were initially identified by their positive reaction with antibodies to von Willebrand factor or human platelet endothelial cell adhesion molecule and their negative response to anti-neurofilament antibodies. Later, vessels were identified by their shape and location. We screened vessels with anti bodies to integrin subunits alpha 1, alpha 2, alpha 3, alpha 5, alpha 6, alpha v, beta 1, beta 3 and beta 4. We found that integrin subunits alpha 6 and beta 4 were consistently found along the whole length of capillary loops and extended to the distal ends of presumed sprouts. The alpha 2 and alpha v integrin concentrations, which are normally low in the microvasculature, were increased on the sprouts. alpha 5 was either absent from vessels entirely or more concentrated on the body than on the sprout. alpha 1 was more commonly present on nerves than blood vessels. These studies suggest an important role for the alpha 6 beta 4 integrin in the initial stages of endothelial outmigration during new vessel growth.