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19 July 1996
Vol 273, Issue 5273

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Endocytic compartment (~600 nanometers in diameter) of a human mononuclear phagocyte revealed by electron microscopy of thin cryosections. Major histocompatibility complex (MHC) class II molecules accumulate in these multilaminar compartments, which may be the major sites where endocytosed protein antigens are encountered. CD1b (smaller, black-stained dots), a non-MHC-encoded molecule that presents bacterial lipid antigens to T cells, also localizes to these compartments. See 349. [Image: P. J. Peters, E. van Donselaar, M. Sugita, and S. A. Porcelli]