IgE-dependent antigen focusing by human B lymphocytes is mediated by the low-affinity receptor for IgE*
In this study we investigated the role of the low-affinity receptor for IgE (FcERII, CD23) on Epstein-Barr virus (EBV)-transformed human B cells in the uptake and presentation to T cells of antigen after complexing with IgE. Cloned EBV-transformed B cells were incubated for 5 h with (4-hydroxy-3-iodo-54trophenyl)acetyl (NIP)-haptenized tetanus toxoid (NIP-TT) or NIP-TT complexed with a chimeric human IgE/mouse anti-NIP monoclonal antibody (IgE x NIP-TT) and then contacted for 2 min with autologous cloned IT-specific T cells. Intracellular Ca2+ mobilization in T cells was determined as an early indicator of T cell activation. The antigen-presenting capacity of B cells was significantly increased by complexing the antigen with IgE. This effect could be selectively reversed in a dose-dependent manner by blocking the FceRII with an anti-CD23 monoclonal antibody. The IgE-mediated increased capacity for presenting antigen became particularly evident when B cells were incubated with NIP-TTor IgE x NIP-'IT for only 1 h at 4 "C, washed and then cultivated for 6 h at 37 "C allowing uptake and processing of the antigen.These results indicate a new role of the FceRII/CD23 molecules in the uptake of antigen by APC which might be of importance in the maintenance of an ongoing immune response against allergens.