Immunoreactivity of the Rho(D) antigen in cytoskeleton-free vesicles

Skeleton-free microvesicles derived from D-positive red cells immunospecifically bind anti-D. Anti-D saturation binding yielded an equilibrium constant value (K = 1-2 X 10(8) I mole-1) similar to intact red cells. The vesicles contained band 3, the major sialoglycoproteins and, at high protein loads, low-molecular-weight polypeptides. Anti-D binding was referenced to total protein, phospholipid, and band 3 content to determine whether there was nonrandom segregation of the D antigen into vesicles. Selective segregation of the D antigen into vesicles could not be demonstrated unequivocally based on the methods and the assumptions of this study. The results, however, indicate that D reactivity does not require a membrane skeletal association.