More than 15 subunits of the integrin family of cell surface adhesion molecules have been identified. The α₆β₄ integrin has recently been identified as a component of hemidesmosomes of stratified squamous epithelium. The monoclonal antibody (mAb) 346-11A binds to the β₄ subunit in mice. Sequence analysis of a cDNA clone coding for this epitope localizes reaction of the mAh to a portion about half way through the extracellular domain at the beginning of the cysteine-rich region.

Sites of β₄ expression in mice were detected by autoradiographic analysis of tissues collected from mice 24 or 48 h after intravenous injection of ¹²⁵I-labeled mAh 346-11A. This non-quantitative technique emphasizes detection of antigen exposed in the vascular space.

These data show that in addition to the epithelia of several organs, the endothelia of intermediate vessels throughout the body are sites of β₄ expression. In particular, endothelium of larger vessels but not capillaries in lung, vessels in thymus, spleen and Peyer’s patches, and portal vessels but not the central veins of the liver, are positive. The expression of the fβ₄ integrin in blood vessels may indicate a specialized function for β₄ at these sites that is distinct from its role in hemidesmo-some-mediated attachment.