Antigen Presentation by Dendritic Cells
Until quite recently, the dogma on immune activation could be summarized as follows: antigens were engulfed and devoured (processed) by a specialized cell, the macrophage, characteristically adherent, phagocytic and radioresistant. A degraded fragment of the consumed antigen then reappeared on the surface of the ingesting cell and was then recognized by a T lymphocyte in association with MHC subregion antigens (H-21 in the mouse) on this same “fresser” cell (presentation) (1). Whilst it is clear that macrophages can certainly ingest and degrade antigens of all shapes and sizes, there is little if any direct evidence that the events defined by the term “presentation” are the responsibility of the same cell. Thus, there is as yet no convincing evidence that antigen fragments are actually re-expressed on the macrophage cell surface let alone that they are presented or associated with macrophage H-21 antigens.
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