title: CD28-induced cytokine production and proliferation by thymocytes are differentially regulated by the p59fyn tyrosine kinase.
abstract: CD28 is a 44-kDa homodimeric receptor that is expressed on the majority of T cells. Engagement of the CD28 receptor by soluble anti-CD28 mAb in conjunction with phorbol ester (PMA) induces the production of cytokines and the proliferation of resting T cells via signal transduction pathways independent of the TCR. Evidence is provided herein that CD28 signals leading to cytokine production do not require the p59fyn (Fyn) tyrosine kinase, whereas CD28-mediated proliferation is dependent on the presence of the Fyn kinase in thymic, but not lymph node, cells. The defect in proliferation is not due to failure of IL-2R signaling, since addition of high concentrations of exogenous IL-2 can overcome the proliferative defect. Analysis of CD28-directed induction of the IL-2R alpha (CD25)-chain, which confers high affinity binding to IL-2, showed that Fyn-deficient thymocytes, but not lymph node cells, failed to up-regulate CD25 expression following anti-CD28 and PMA stimulation. Thus, the Fyn tyrosine kinase is critically required for thymic CD28-mediated CD25 expression and proliferation but not for CD28-mediated cytokine production.
authors.affiliation: Department of Microbiology and Immunology, University of British Columbia, Vancouver, Canada.
authors.forename: C J
authors.initials: CJ
authors.lastname: Ong
authors.forename: A S
authors.initials: AS
authors.lastname: Lim
authors.forename: H S
authors.initials: HS
authors.lastname: Teh
mesh_terms: D000818:Animals; D000911:Antibodies, Monoclonal / Q000494:pharmacology; D018106:CD28 Antigens / Q000187:drug effects / Q000276:immunology / Q000502:physiology*; D002455:Cell Division / Q000187:drug effects; D002478:Cells, Cultured; D005260:Female; D007376:Interleukin-2 / Q000494:pharmacology; D008198:Lymph Nodes / Q000166:cytology; D008213:Lymphocyte Activation / Q000187:drug effects; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D008822:Mice, Transgenic; D009928:Organ Specificity; D010766:Phosphorylation; D011499:Protein Processing, Post-Translational; D011518:Proto-Oncogene Proteins / Q000172:deficiency / Q000502:physiology*; D051076:Proto-Oncogene Proteins c-fyn; D011948:Receptors, Antigen, T-Cell / Q000276:immunology; D015375:Receptors, Interleukin-2 / Q000096:biosynthesis / Q000187:drug effects / Q000235:genetics / Q000502:physiology; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology*; D013601:T-Lymphocytes / Q000187:drug effects / Q000276:immunology*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D013950:Thymus Gland / Q000166:cytology
chemical_list: D000911:Antibodies, Monoclonal; D018106:CD28 Antigens; D007376:Interleukin-2; D011518:Proto-Oncogene Proteins; D011948:Receptors, Antigen, T-Cell; D015375:Receptors, Interleukin-2; C494960:Fyn protein, mouse; D051076:Proto-Oncogene Proteins c-fyn; D013755:Tetradecanoylphorbol Acetate