Endocytic routes of exogenous antigen in murine dendritic cells and macrophages

Objective To compare the endocytic routes of exogenous antigen between murine dendritic cells (DCs) and macrophages (M phis). Methods Murine bone marrow-derived DCs and peritoneal M phis were pulsed with horseradish peroxidase (HRP)-5 nm colloidal gold for 10 minutes, then grouped and chased for 0 - 120 minutes in culture medium. Intracellular distribution of 5 nm colloidal gold was explored by means of the cellular enzymatic-chemistry of acid phosphatase and MHC II immuno-cytochemistry under electron microscope. Results After 10 minutes of pulse with HRP-5 nm colloidal gold and 30 minutes of chase, most HRP-5 nm gold particles internalized by DCs entered into MHC class II. compartments (M II Cs), and a small portion entered into acid phosphatase-positive lysosomes. In contract to DCs, most M phis lysosomes were accessed by HRP-5 nm gold particles, and a small portion of HRP-5 nm gold particles entered into M II Cs. After 60 minutes of chase, 5 nm gold particles could hardly be seen within M phis, whereas most 5 nm gold particles were still retained in DCs. Conclusions The endocytic route of exogenous antigen in DCs seems to be different from that in M phis. Antigens taken by M phis mainly enter into lysosomes within 30 minutes. In the case of DCs, most internalized antigens enter into M II Cs, which may be related to their unique antigen-presenting function. In addition, M phis seem to have more powerful capacity to scavenge exogenous antigen than DCs.