Radically altered T cell receptor signaling in glycopeptide-specific T cell hybridoma induced by antigen with minimal differences in the glycan group.

A T cell hybridoma raised against the synthetic glycopeptide T-72(Tn) was used to study whether the initial TCR signaling events are markedly different when the hybridoma is stimulated with glycopeptides closely related to the cognate glycopeptide antigen. T-72(Tn) has an alpha -D-GalNAc group C-linked to the central threonine in the decapeptide VITAFTEGLK, and the hybridoma is known to be highly specific for this carbohydrate group. T-72(Tn)-pulsed APC induced tyrosine phosphorylation of the TCR-zeta 21 - and 23-kDa proteins and the downstream p42/44 MAP kinase and strong IL-2 secretion. APC pulsed with T-72(alpha -D-GlcNAc), which differs from T-72 (Tn) solely by the orientation of a hydroxy group in the carbohydrate structure, completely failed to induce detectable tyrosine phosphorylation and IL-2 secretion. APC pulsed with S-72(Tn), which differs from T-72(Tn) by not having a methyl group in the serine amino acid side chain to which the glycan is attached, induced partial tyrosine phosphorylation of the TCR-zeta 21-kDa protein, no tyrosine phosphorylation of the MAP kinases and no IL-2 production. Molecular modeling of the MHC/glycopeptide complex revealed that the dramatic difference between the stimulatory power of T-72(Tn) and T-72(alpha -D-GlcNAc) is mainly due to very small differences in the TCR exposed carbohydrate structure.