Alpha-macroglobulin-induced release of anti-Ig-coated particles from a subpopulation of rabbit B lymphocytes

Approximately half of the rosettes formed by rabbit Ig+ lymphocytes (B cells) and anti-coated erythrocytes or glutaraldehyde-fixed bacteria are dissociated upon the addition of rabbit serum. Rabbit serum was fractionated and the rosette-dissociating activity was found in purified preparations of rabbit alpha 1- and alpha 2-macroglobulins. Studies designed to elucidate the mechanism of rosette dissociation suggested that the alpha-macroglobulins dissociated rosettes by causing the release or proteolytic cleavage of the membrane proteins complexed with the anti-Ig-coated particles. These data suggest that the alpha-macroglobulins may have a role in the interaction of B lymphocytes with particulate antigens.