Endocytic Activity of Dendritic Cells is Similar to Other Antigen Presenting Cells

Abstract

Antigen processing occurs prior to presentation of an exogenous antigen in association with class II MHC, and requires endocytosis of antigen followed by partial digestion. The intra-cellular pathways taken by antigen and class II may vary between cells, ¹ but most evidence suggests that antigen-derived peptides bind class II in organelles related to late endosomes. ² Antigens enter the endocytic pathway either in the fluid phase or bound to internalized plasma membrane. Processing is enhanced by antigen receptors which are endocytosed from the plasma membrane, examples of which are found on all APC types except dendritic cells: surface immunoglobulin (slg) on B cells, ³ opsonin receptors (FcR/C3R/C4R) on B cells and macrophages⁴ and scavenger receptors on macrophages. ⁵ Therefore, endocytosis in dendritic cells occurs by the less efficient means of fluid-phase endocytosis and non-specific membrane absorption. These mechanisms appear to be sufficient to allow processing of at least some exogenous antigens by dendritic cells. ^{6, 7}