Positional Effect of Amino Acid Replacement on Peptide Antigens for the Increased IFN-γ Production from CD4T Cells

Abstract

Based on the fact that site-specific amino acid replacement on peptide antigens stimulated T cell clones to produce increased amount of IFN-γ, we investigated this structure-function relationship, using various peptide analogues. We used three human Th0 clones (BC20.7,BC33.5 and BC42.1) that express distinct TCRα and TCRβ chains, but recognize the same TCR ligand ; i.e., the same framework of peptide antigen BCGa p84-100 in the context of DRB1*1405. These T cells were stimulated with various peptide analogues, followed by determination of proliferative responses and IFN-γ production. Replacement of Leu at peptide position 2 (P2) by amino acids which are less hydrophobic than the wild type (Val, Ala) or those with similar structural or neutral charge (Thr, Ser), induced increased IFN-γ production from T cells. This phenomenon was associated with structural features of TCR, especially the length of CDR3 region of TCRα. Amino acid replacement at the other positions did not induce increased IFN-γ production. Amino acid substitution at P2 frequently induces increased IFN-γ production in a clone-specific manner, which is associated with the structure of CDR3 in TCRVα chains.