TCR alpha beta-independent CD28 signaling and costimulation require non-CD4-associated Lck.
Whether the sequelae of signals generated through CD28 either directly or in circumstances of costimulation require proximal events mediated by p56lck remains contentious. We demonstrate that CD4-, but not CD4+ clonal variants respond to CD28-specific mAb with both early and late indicators of activation. Forced expression of A418/A420-mutated CD4 or wild-type CD4 in the CD4- variant recapitulated the CD28-mediated responses of the CD4- and CD4+ variants, respectively. The implicated involvement of non-CD4-associated Lck is formally demonstrated by overexpressing S20/S23 Lck or wild-type Lck in CD4+ variants. The former, but not latter, rescues direct CD28 signaling, and supports costimulation. The results demonstrate that constitutive levels of non-CD4-associated Lck functionally limit CD28-mediated signaling.
Department of Immunology, University of Toronto, Arthritis and Immune Disorder Research Centre, Ontario, Canada.
B L
BL
Leung
L
L
Haughn
A
A
Veillette
R G
RG
Hawley
R
R
Rottapel
M
M
Julius
D000818:Animals; D000911:Antibodies, Monoclonal / Q000494:pharmacology; D018106:CD28 Antigens / Q000235:genetics / Q000276:immunology / Q000502:physiology*; D015704:CD4 Antigens / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*; D002455:Cell Division / Q000276:immunology; D002460:Cell Line; D002999:Clone Cells; D003545:Cysteine / Q000235:genetics; D005822:Genetic Vectors; D008213:Lymphocyte Activation / Q000276:immunology*; D019860:Lymphocyte Specific Protein Tyrosine Kinase p56(lck) / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008817:Mice, Mutant Strains; D016693:Receptors, Antigen, T-Cell, alpha-beta / Q000276:immunology / Q000502:physiology*; D012190:Retroviridae / Q000235:genetics / Q000276:immunology; D015398:Signal Transduction / Q000276:immunology*; D016176:T-Lymphocyte Subsets / Q000166:cytology / Q000201:enzymology / Q000276:immunology / Q000378:metabolism
D000911:Antibodies, Monoclonal; D018106:CD28 Antigens; D015704:CD4 Antigens; D016693:Receptors, Antigen, T-Cell, alpha-beta; D019860:Lymphocyte Specific Protein Tyrosine Kinase p56(lck); D003545:Cysteine