The Release of Antigen Molecules from Macrophages: Characterization of the Phenomena

Abstract

Abstract Macrophages were pulsed with 125I-labeled hemocyanin and then cultured in media devoid of any radioactive material. A great part of the cell-bound 125I was released into the culture fluid in a form not bound to protein; however, a small amount (3 to 7%) was released as protein-bound 125I. The released protein-bound 125I was associated with live, viable macrophages and did not derive from dishes nor from lysis of dead cells. About ¼ of the released protein was immunochemically reactive with anti-keyhole limpet hemocyanin (KLH); the remaining ¾ most likely represents KLH in which the immunoreactive groups lost their original conformation. Trypsin treatment of macrophages did not affect the release of 125I-KLH, suggesting that the product derives from the cell interior. A great majority of the 125I KLH tends to be of smaller size than the original molecule. The release of KLH decreases with time of culture but can be reactivated if fresh medium is added. We conclude that the cell conserves a small pool of intracellular antigen in a form or in a compartment which is slowly catabolized; from this pool a small amount is slowly released into the cell exterior, probably by a process akin to endocytosis but in reverse.