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The Release of Antigen Molecules from Macrophages: Characterization of the Phenomena¹

From the Department of Pathology, Harvard Medical School, Boston, Massachusetts 02115

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 of the released protein was immunochemically reactive with anti-keyhole limpet hemocyanin (KLH); the remaining 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.

Footnotes

¹ This work was supported by National Institutes of Health Grant AI 10091.

² Dr. Calderon is supported by an International Exchange Fellowship of the Public Health Service.

³ Dr. Unanue is a recipient of a Research Career Award from the National Institutes of Health.