Schiff base-mediated co-stimulation primes the T-cell-receptor-dependent calcium signalling pathway in CD4 T cells.
In addition to macromolecular interactions that provide co-stimulation during antigen-presenting cell (APC) and CD4+ T-cell conjugation, covalent chemical events between specialized ligands have been implicated in T-cell co-stimulation. These take the form of transient Schiff base formation between carbonyls and amines expressed on APC and T-cell surfaces. Small Schiff base-forming molecules, such as tucaresol, can substitute for the physiological donor of carbonyl groups and provide co-stimulation to T cells, thereby functioning as orally active immunopotentiatory drugs. The Schiff base co-stimulatory pathway in T cells has been partially characterized in terms of changes in Na+ and K+ transport, and activation of the mitogen activated protein kinase (MAPK) ERK2. In the present study, the effects of Schiff base co-stimulation by tucaresol on the T-cell receptor (TCR)-dependent pathway leading to Ca2+ release were investigated. Schiff base co-stimulation by tucaresol was found to prime for enhanced TCR-dependent phospholipase C-gamma phosphorylation, inositol 1,4,5-triphosphate production, and Ca2+ mobilization that correlated with functional enhancement of interleukin-2 production in primary T cells. The effects on Ca2+ occurred comparably in Jurkat and primary CD4+ T cells responding to anti-CD3 monoclonal antibody. Enhancement of the Ca2+ response required a 10-min priming period and was prevented by prior covalent ligation of cell-surface free amino groups by sulpho-N-hydroxy succinimido-biotin; clofilium-mediated inhibition of tucaresol-induced changes in intracellular K+; and selective inhibition of the MAPK pathway. The data are consistent with a priming mechanism in which late co-stimulation-triggered events exert a positive influence on early TCR-triggered events. In additional studies of murine T cells expressing trans-gene TCRs, tucaresol was likewise shown to prime for enhanced Ca2+ mobilization in response to physiological TCR-engagement by MHC-peptide complexes.
Hall
S R
SR
Department of Immunology and Virology, GlaxoSmithKline Research and Development, Medicines Research Centre, Stevenage, UK. srh18219@gsk.com
Rhodes
J
J
D000588:Amines / Q000037:antagonists & inhibitors; D000818:Animals; D001547:Benzaldehydes / Q000276:immunology; D001565:Benzoates / Q000276:immunology; D017252:CD3 Complex / Q000378:metabolism; D015496:CD4-Positive T-Lymphocytes / Q000276:immunology*; D002118:Calcium / Q000378:metabolism*; D018929:Cell Culture Techniques; D002460:Cell Line; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D007376:Interleukin-2 / Q000096:biosynthesis; D007527:Isoenzymes / Q000378:metabolism; D008213:Lymphocyte Activation / Q000276:immunology*; D051379:Mice; D008807:Mice, Inbred BALB C; D008822:Mice, Transgenic; D020929:Mitogen-Activated Protein Kinase Kinases / Q000037:antagonists & inhibitors; D051966:Phospholipase C gamma; D010766:Phosphorylation; D026902:Potassium Channel Blockers; D011948:Receptors, Antigen, T-Cell / Q000276:immunology*; D012545:Schiff Bases / Q000276:immunology*; D010738:Type C Phospholipases / Q000378:metabolism
D000588:Amines; D001547:Benzaldehydes; D001565:Benzoates; D017252:CD3 Complex; D004791:Enzyme Inhibitors; D007376:Interleukin-2; D007527:Isoenzymes; D026902:Potassium Channel Blockers; D011948:Receptors, Antigen, T-Cell; D012545:Schiff Bases; D020929:Mitogen-Activated Protein Kinase Kinases; D010738:Type C Phospholipases; D051966:Phospholipase C gamma; C059629:tucaresol; D002118:Calcium