T-Cell Antigen Receptor Peptides Inhibit Signal Transduction within the Membrane Bilayer

Previous studies have shown that a synthetic peptide (core peptide, CP) corresponding to a 9-amino-acid region in the transmembrane domain of the α subunit of the T-cell antigen receptor (TCR) can suppress T-cell function in vitro and in vivo. The aim of these experiments was to determine the cellular site and molecular mechanism of CP inhibition in T cells. The cytochrome c-sensitive TCR-expressing hybridoma (2B4) was stimulated with pigeon cytochrome c antigen, anti-CD3 crosslinking, or PMA and ionomycin, in the presence or absence of CP, and the resulting IL-2 produced was measured in a bioassay using an IL-2-dependent cell line (CTLL-2). In the presence of CP, IL-2 production was inhibited following antigen-induced stimulation. By contrast, when stimulated with cross-linking antibodies to the CD3 complex or with PMA and ionomycin, both of which activate T cells downstream of the TCR antigen recognition site, CP had no effect on IL-2 production. These experiments suggest that CP interferes with TCR function by inhibiting T-cell activation at the transmembrane/receptor level. In addition, we show that CP inhibits early TCR signal transduction events such as TCR ζ chain phosphorylation following stimulation with either antigen or anti-CD3-crosslinking antibodies, although this is unlikely to be the mechanism leading to the reduced IL-2 production.