ABSTRACT
In the immune system, transient and specific adhesions between cells are common-place. The adhesions are transient so that the highly mobile cells involved, including macrophages and lymphocytes, do not become permanently stuck to one another. This chapter argues that in cell-cell adhesions there is competition between specific bonding and nonspecific repulsion such that the particular receptors become highly concentrated in relatively small areas of cell-cell contact. Thus, the adhesive interaction that involves bonding between receptors on two different cells may achieve many of the same results as crosslinking of receptors on either cell because, in either case, a high local concentration of receptors is achieved in the membrane of the cell. The chapter explains why the adhesions are transient; one or both cells must do something active to terminate the adhesion, and some possibilities. Antigens, and/or fragments thereof, are evidently involved in the adhesion of lymphocytes to one another or to antigen-pressing cells.
