Ligand-induced association of surface immunoglobulin with the detergent-insoluble cytoskeletal matrix of the B lymphocyte

Ligand binding is believed to induce surface immunoglobulin (Ig) to form a physical association with the underlying cell cytoskeleton. We investigated this interaction by use of nonionic detergents, which are known to dissolve membrane proteins but preserve a detergent-treatment, surface Ig in the B cell plasma membrane was fully dissolved by nonionic detergent; however, interaction with a ligant converted the receptor to a novel, to a detergent-insoluble form required receptor cross-types of experiments demonstrated that this form of Ig was not due to the size insolubility of immune complexes and involved a stable, noncovalent association of the receptor with the detergent-insoluble, cytoskeletal residue. Incubation of ligand-bound cells at 37°C promoted the degradation of surface Ig and the appearance of new, lower m.w. species, including a major soluble protein (50,000 daltons) that was antigenically related to surface Ig. These events corresponded to receptor endocytosis by several criteria (time course, temperature sensitivity, and energy dependence). Taken together, these results were consistent with the ligand-induced transmembrane attachment of receptors to the underlying cytoskeletal matrix followed by receptor internalization and catabolism.