Identification of desmosomal surface components (desmocollins) and inhibition of desmosome formation by specific Fab

Specific antibodies against the components of desmosomes, the adhesive junctions of epithelial cells, have been used to determine which components are located on the cell surface. Three criteria have been used: fluorescent antibody staining, immuno-gold labelling and electron microscopy, and quantitative measurements of antibody binding using [1251]protein A. When these techniques were applied to living Madin-Darby bovine kidney (MDBK) cells, antibodies against only two des-mosomal components, glycoproteins of approximately 115X 103A/r and 100xl03Mr, bound to the cell surface. Antibodies against all other components, the 230 and 205xl03A/r proteins (desmo-plakins), the 15OxlO3Afr glycoprotein and the 82 and 86XlO3A/r proteins reacted in fluorescent antibody staining only after cells had been fixed and made permeable. MDBK cells were cultured in the presence of univalent fragments (Fab') of anti-desmosomal antibodies for periods from 24 h to 72h. After these times cells were fixed, made permeable, and stained with anti-desmoplakin antibody to assay for desmosome formation. Fab ' derived from anti-100xl03Mr protein specifically inhibited desmosome formation, whereas Fab's from anti-desmoplakin, anti-150xl03Mr and anti-82 and 86xlO3JWr proteins were without effect. We conclude that the 100xl03A/r and the immunologically related 115xl03A/r components ar