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 u sed to study whether the initial TCR signaling events are markedly differen t when the hybridoma is stimulated with glycopeptides closely related to th e cognate glycopeptide antigen. T-72(Tn) has an alpha -D-GalNAc group C-lin ked to the central threonine in the decapeptide VITAFTEGLK, and the hybrido ma is known to be highly specific for this carbohydrate group. T-72(Tn)-pul sed APC induced tyrosine phosphorylation of the TCR-zeta 21 - and 23-kDa pr oteins 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 t he orientation of a hydroxy group in the carbohydrate structure, completely failed to induce detectable tyrosine phosphorylation and IL-2 secretion. A PC 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, n o tyrosine phosphorylation of the MAP kinases and no IL-2 production. Molec ular modeling of the MHC/glycopeptide complex revealed that the dramatic di fference 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 s tructure.