Antibody-mediated internalization of B lymphocyte surface membrane immunoglobulin

The ultrastructural correlates of antibody-mediated internalization of membrane immunoglobulin determinants has been studied in the guinea pig using a horseradish peroxidase conjugate of rabbit anti-guinea pig immunoglobulin. We have observed that polar flow of ligand-induced micro-aggregated membrane immunoglobulin proceeds by local deformation of the plasma membrane into open-ended endocytic vesicles which in turn accumulate at the Golgi-associated pole prior to completion of endocytosis. 'Capping' does not appear to result from simple diffusion of the aggregates within the plane of the membrane. In addition, the question of whether anti-immunoglobulin can induce the formation of uropods on B lymphocytes in the guinea pig was examined. Formation of uropod-like structures on B lymphocytes appears to be factitious and induced by accumulation at the Golgi-associated cell pole of non-internalizable aggregates of membrane immunoglobulin linked to cell debris. These observations are interpreted as supporting the concept that spontaneous uropod formation by lymphocytes in the absence of anti-immunoglobulin reagents is a characteristic of antigen-reactive thymus-derived lymphocytes in the guinea pig.