title: IL-12 plays a significant role in the apoptosis of human T cells in the absence of antigenic stimulation.
abstract: Interleukin-12 (IL-12) is an immunoregulatory cytokine that plays an essential role in cell-mediated immunity. It is known to induce T cell apoptosis in in vivo systems such as graft-versus-host disease (GVHD) and experimental autoimmune uveitis (EAU). However, the role of IL-12 in T cell apoptosis in the absence of antigenic stimulation has not been clearly defined. This study was conducted to investigate whether IL-12, in the absence of an antigen, is able to induce T cell apoptosis, and also, which signalling pathways utilized by IL-12 are involved in this process. Our data clearly showed that IL-12 in the absence of an antigen induces apoptosis in T cells. Flow cytometry and ELISA showed FasL up-regulation and increased IFN-gamma synthesis in IL-12 treated T cells, while Fas and TNF-R1 showed little change. Semi-quantitative RT-PCR demonstrated that IL-12 was able to up-regulate TNF-alpha and FasL mRNA expression. Furthermore, IL-12 induced apoptosis was associated with caspase-3, caspase-2, caspase-7, DNA fragmentation factor 45 (DFF45) and Fas associated death domain (FADD) whereas TNF receptor associated death domain (TRADD) and receptor interacting protein (RIP) were not. Inhibition of Janus tyrosine kinase (JAK) was able to suppress IL-12 induced T cell apoptosis. Anti-FasL antibody was able to block IL-12 induced T cell apoptosis. In conclusion, our findings suggest that IL-12 is able to induce T cell apoptosis in the absence of an antigen. In addition, the present data suggest that this process is FasL mediated and caspase-3 dependent. Furthermore, JAK was shown to be involved in this process. These results may have significant implications in the understanding of IL-12 mediated T cell apoptosis.
authors.affiliation: Department of Medicine, Howard University, Washington, DC, USA.
authors.forename: Hongtao
authors.initials: H
authors.lastname: Fan
authors.forename: Curla S
authors.initials: CS
authors.lastname: Walters
authors.forename: Georgia M
authors.initials: GM
authors.lastname: Dunston
authors.forename: Robert
authors.initials: R
authors.lastname: Tackey
mesh_terms: D000911:Antibodies, Monoclonal / Q000378:metabolism; D000941:Antigens / Q000378:metabolism*; D017209:Apoptosis; D051017:Apoptosis Regulatory Proteins; D029681:Arabidopsis Proteins; D015153:Blotting, Western; D053148:Caspase 3; D020169:Caspases / Q000096:biosynthesis / Q000378:metabolism; D002469:Cell Separation; D053938:DNA Fragmentation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004797:Enzyme-Linked Immunosorbent Assay; D053222:Fas Ligand Protein; D044943:Fatty Acid Desaturases / Q000096:biosynthesis; D005434:Flow Cytometry; D006801:Humans; D020287:In Situ Nick-End Labeling; D007371:Interferon-gamma / Q000096:biosynthesis; D018664:Interleukin-12 / Q000378:metabolism / Q000502:physiology*; D053613:Janus Kinase 1; D008562:Membrane Glycoproteins / Q000096:biosynthesis; D014176:Protein Biosynthesis; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors; D011506:Proteins / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D053422:Receptor-Interacting Protein Serine-Threonine Kinases; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction; D013601:T-Lymphocytes / Q000473:pathology*; D047990:TNF Receptor-Associated Factor 1; D013997:Time Factors; D014407:Tumor Cells, Cultured; D020032:Tyrphostins / Q000494:pharmacology; D015854:Up-Regulation
chemical_list: D000911:Antibodies, Monoclonal; D000941:Antigens; D051017:Apoptosis Regulatory Proteins; D029681:Arabidopsis Proteins; D004791:Enzyme Inhibitors; C505661:FASLG protein, human; D053222:Fas Ligand Protein; D008562:Membrane Glycoproteins; D011506:Proteins; D012333:RNA, Messenger; D047990:TNF Receptor-Associated Factor 1; D020032:Tyrphostins; C095512:alpha-cyano-(3,4-dihydroxy)-N-benzylcinnamide; C109664:caspase-activated DNase inhibitor; D018664:Interleukin-12; D007371:Interferon-gamma; D044943:Fatty Acid Desaturases; C084083:Fad7 protein, Arabidopsis; D011505:Protein-Tyrosine Kinases; C507904:JAK1 protein, human; D053613:Janus Kinase 1; C506249:RIPK1 protein, human; D053422:Receptor-Interacting Protein Serine-Threonine Kinases; C505407:CASP3 protein, human; D053148:Caspase 3; D020169:Caspases