Half-life of antigen/major histocompatibility complex class II complexesin vivo: intra- and interorgan variations

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Abstract
We have determined the half‐life in vivo of antigen/MHC class II complexes in different organ microenvironments. Mice were “pulsed” with myoglobin intravenously and MHC class II‐positive antigen‐presenting cell (APC) populations from different organs were isolated after various time intervals. Specific antigen/MHC complexes were quantitated by co‐cultivation of the APC subsets with myoglobin‐specific T‐T hybridoma cells in vitro. Half‐lives of antigen/MHC complexes differed both between organs and between compartments of the same organ. Half‐lives in peripheral organs (spleen and bone marrow) ranged between 3 and 8 h, whereas in the thymus half‐lives between 13 h (cortical epithelial cells) and 22 h (medullary dendritic cells) were observed. Half lives in vivo were independent of antigen processing, since intact protein or antigenic peptides yielded similar values. The considerably longer half‐life of peptide/MHC complexes in the thymus as compared to peripheral organs may reflect the distinct role which antigen presentation plays in both organs, i.e. induction of tolerance versus induction of immunity.