ANTIGEN PRESENTATION IS ENHANCED BY TARGETING ANTIGEN TO THE FC-EPSILON-RII BY ANTIGEN-ANTI-FC-EPSILON-RII CONJUGATES

Targeting Ag to the Fc epsilon RII by Ag-specific IgE has been shown t o be an efficient means of enhancing Ag presentation by B cells to Ag- specific T cells. To take advantage of the Fc epsilon RII as a targeti ng molecule and to investigate whether IgE was required for mediation of the enhanced stimulation, Ag was covalently coupled to anti-Fc epsi lon RII by using heterobifunctional crosslinking reagents. These Ag-Ab conjugates were used with T cell lines specific for the Ags, OVA (BB6 .5) or rabbit gamma-globulin (CDC35 and D1.6), and splenic B cells to examine both B cell and T cell proliferation in vitro. Significant pre sentation of Ag-anti-Fc epsilon RII conjugates was apparent at doses o f Ag 1,000- to 10,000-fold lower than seen with unconjugated Ag alone. Ag presentation with the use of anti-Fc epsilon RII-Ag conjugates was as good as or better than conjugates with Ab to the adhesion molecule Pgp-1 or control Ab in T cell proliferation and better than those con jugates in B cell proliferation assays (10- to 100-fold). Anti-Fc epsi lon RII-Ag conjugates were clearly more effectively presented than Ag- anti-Fc gamma RII conjugates (>100-fold). Mouse Fc epsilon RII is pres ently known to be expressed on B cells and follicular dendritic cells and these in vitro results suggest that the conjugates would be useful tools for investigating the role of IgE-mediated B cell Ag presentati on in vivo. BALB/c mice immunized with OVA-anti-Fc epsilon RII conjuga tes made a quite significant OVA-specific IgG1 response and a detectab le IgE response. No detectable Ab was produced in response to OVA alon e and a minimal response was seen when an isotype-matched control conj ugate was used. Thus, the results indicate that Fc epsilon RII targeti ng is operative both in vivo and in vitro.