The biochemistry of cell-adhesion

The proposition is examined that adhesion between cells of animal tissues, and between cells and their extracellular matrix, is brought about by specific molecules present at cell-surfaces. Evidence is surveyed which has begun to emerge from the use of antibodies which inhibit or reverse adhesion. Putative cell-adhesion molecules in cellular slime-moulds and cells of chick and mouse embryos have been identified by their ability to neutralize the adhesion-inhibiting activity of monovalent fragments of polyspecific antibodies. In some instances antibodies have also been used to investigate the role of the cell-adhesion molecules in morphogenetic phenomena. A possible parallel is discussed between the effects of calcium ions on the cell-adhesion molecule uvomorulin from mouse blastomeres, and its effects on certain other cell-adhesion molecules.Although the role of fibronectin in promoting attachment and spreading of cells on artificial substrates and on denatured collagen is firmly established, there is little evidence that this glycoprotein is involved in direct intercellular adhesion. The observation that cells spread on adsorbed fibronectin, whereas binding of individual fibronectin molecules to cells is difficult to demonstrate may merely indicate that fibronectin is a relatively weak ligand for cell-surfaces. It is suggested that rather than being a necessary intermediate in the adhesion of cells to collagen, fibronectin may form matrix in its own right which shares with native collagen the ability to promote cell-attachment and spreading.The long-held view that cell-surface oligosaccharides act as receptors in cell-adhesion appears still to be largely unsubstantiated. However the poorly adhesive properties of cells from many different lines with glycosylation defects strongly suggest N-linked oligosaccharides of glycoproteins are involved in some way as yet not determined.