HUMAN DENDRITIC CELLS HANDLING OF BINDING, UPTAKE AND DEGRADATION OF FREE AND IGG-IMMUNE COMPLEXED DINITROPHENYLATED HUMAN SERUM-ALBUMIN IN-VITRO

The handling of free and IgG-complexed dinitrophenylated human serum a lbumin (DNP-HSA) by human dendritic cells (DC) cultured with granulocy te-macrophage colony-stimulating factor (GM-CSF) and interleukin-4 (IL -4) was studied. It has been shown that the amount of uncomplexed or I gG-complexed antigen required by DC to start an immune response is low compared with other antigen-presenting cells. We therefore examined w hether such efficient presentation of immune complexes is due to an en hanced Fc gamma RII-mediated endocytosis or to a specialized and effic ient antigen handling, i.e. macropinocytosis. The Fc gamma RII express ion was found to be heterogeneous on the GM-CSF- and IL-4-cultured DC, i.e. it ranges from low to high expression. The handling of antigen a nd immune complexes revealed, that the level of binding and uptake of IgG-DNP-HSA complexes by in vitro expanded DC is low compared with fre e antigen. Uncomplexed DNP-HSA is probably handled either by endocytos is via receptors being more abundant and/or efficient than the Fc gamm a RII or via non-receptor-mediated endocytosis. The binding and uptake of IgG-complexed DNP-HSA was blocked by anti-Fc gamma RII antibody, i ndicating the specificity of the interaction.