Self γ2ab Protein Is Presented in Vivo by γ2ab B Cells but Not by Dendritic Cells

We have previously shown that IgG2a^b Ig does not induce tolerance in MHC class II restricted CD4 T cells in a TCR transgenic model and that anti-IgC2a^b transgenic T cells specific for peptide 435-451 are indeed present in the periphery where they interact with γ2a^b-positive B cells. We also observed that because T cell tolerance depends on the presentation of self peptides, it was probable that IgG2a^b was not easily processed and presented in vivo. In this study, we have investigated the presentation of naturally processed γ2a^b (435-451) determinants to specific T cells. Dendritic cells, macrophages, and B cells were purified from the spleens of Igh-1b mice. These cells were then functionally tested for the presence of specific peptide-MHC complexes. The results showed that, in vivo, γ2a^b-producing B cells, but not dendritic cells, are the only APCs able to present this self peptide. This indicates that recognition of the IgG2a^b-self peptide is exclusively mediated by T-B cell interaction.