No abstract

In the course of screening immunoglobulin G (IgG) sequences for T cell epitopes, we identified novel Treg epitope peptides, now called Tregitopes, contained in the highly conserved framework regions of Fab and Fc. Tregitopes may provide one explanation for the expansion and stimulation of Treg cells following intravenous immunoglobulin (IVIg) therapy. Their distinguishing characteristics include in silico signatures that suggest high-affinity binding to multiple human HLA class II DR and conservation across IgG isotypes and mammalian species with only minor amino acid modifications. Tregitopes induce expansion of CD4(+)/CD25(hi)/FoxP3(+) T cells and suppress immune responses to co-incubated antigens in vitro. By comparing the human IgG Tregitopes (hTregitopes 167 and 289, located in the IgG CH1 and CH2 domains) and Fab to murine sequences, we identified class II-restricted murine Tregitope homologs (mTregitopes). In vivo, mTregitopes suppress inflammation and reproducibly induce Tregs to expand. In vitro studies suggest that the Tregitope mechanism of action is to induce Tregs to respond, leading to production of regulatory signals, followed by modulation of dendritic cell phenotype. The identification of Treg epitopes in IgG suggests that additional Tregitopes may also be present in other autologous proteins; methods for identifying and validating such peptides are described here. The discovery of Tregitopes in IgG and other autologous proteins may lead to the development of new insights as to the role of Tregs in autoimmune diseases.

No abstract

Tetramers of major histocompatability complex molecules (MHC) are now well-established reagents for the detection of antigen-specific T cells by flow cytometry. MHC tetramers are prepared by mixing enzymatically biotinylated MHC molecules with commercial preparations of streptavidin, usually conjugated to a fluorescent phycobiliprotein such as phycoerythrin (PE) or allophycocyanin (APC). While data obtained with MHC tetramers prepared with small molecule fluorophores has been reported, considerable lot-to-lot variation among conventional streptavidin conjugates to small molecules prevents routine preparation of such reagents. We now report robust preparation of MHC tetramers with small molecule fluorophores, using a recombinant mutant of streptavidin incorporating a carboxy-terminal cysteine in each of the four identical subunits that is conjugated to maleimide derivatives of any of several small molecule fluorophores. These reagents significantly expand the versatility of the MHC tetramer methodology.

No abstract