FcγRII on Human B Cells Can Mediate Enhanced Antigen Presentation

The ability of FcγR on monocytes and macrophages to enhance presentation of Ab-bound Ag has been well established. In contrast, studies suggest that FcγRII on B cells functions primarily to suppress B cell responses. We found that presentation of tetanus toxoid (TT) by human EBV-transformed B cells was enhanced by 100- to 1000-fold, when TT was targeted to FcγRII on B cells by using a conjugate consisting of TT covalently linked to anti-human FcγRII mAb 41H16. This enhanced presentation could be blocked by mAb 41H16, heat-aggregated human IgG, or anti-MHC Class II mAb. Similarly, multimeric immune complexes composed of TT and anti-TT mAb, SA13, and 9F12 also enhanced presentation of TT. Furthermore, FcγRII on purified human peripheral blood B cells could also enhance Ag presentation. These studies provide the first clear evidence that FcγRII can participate in enhanced Ag presentation by human B cells, and suggest that FcγRII has the potential to play a stimulatory role in human B cell responses to Ag–Ab complexes.