SPECIFIC ANTIGEN TARGETING TO SURFACE IGE AND IGG ON MOUSE BONE-MARROW-DERIVED MAST-CELLS ENHANCES EFFICIENCY OF ANTIGEN PRESENTATION

The discovery that bone marrow-derived mast cells can express major hi stocompatibility complex class II molecules and act as antigen-present ing cells prompted us to evaluate this function when antigen is intern alized through fluid-phase endocytosis or via specific uptake by using IgG and IgE antibodies. This study was performed using a specific T-c ell hybridoma developed against Lol p 1, the major allergen of grass p ollen Lolium perenne. Expression of Fc gamma R and Fc epsilon RI by ma st cells led us to investigate the influence of IgG- and IgE-targeted antigen on the antigen-presenting function of mast cells. Internalizat ion of Lol p 1 through different specific IgG monoclonal antibodies (m Ab) resulted in the activation of Lol p 1-specisc T-cell hybridoma at concentrations about 100-fold less than that required for T-cell stimu lation by uncomplexed antigen. IgE-complexed Lol p 1, which facilitate s trapping of antigen by mast cells, induced an accelerated and more e fficient antigen-presenting capacity of mast cells than that obtained with uncomplexed antigen. However, aggregation of anti-dinitrophenyl ( DNP) IgE mAb by the irrelevant antigen DNP-human serum albumin did not substantially increase the capacity of mast cells to present Lol p 1 to T cells. This suggests that the mere aggregation of Fc epsilon RI i s not sufficient for enhanced antigen presentation mediated by IgE. Ti ssue distribution and strategic location of mast cells at the mucosal barriers and their capacity to process the antigen through efficient f luid-phase pinocytosis as well as IgG- and IgE-dependent targeting of antigens provide mast cells with a prominent role in immune surveillan ce.