Differential regulation of activation-induced cell death in individual human T cell clones.
BACKGROUND
Restimulation of T lymphocytes via the TCR/CD3 complex can result in CD95/CD95L-dependent activation-induced cell death (AICD). Although the correlation of AICD sensitivity to the T helper 1 phenotype was confirmed in different studies, the underlying mechanism is still debated. Thus, it has been suggested that in Th2 cells, AICD resistance is controlled by a TCR-induced upregulation of the CD95-associated inhibitory phosphatase, FAP-1. We and others demonstrated that AICD resistance is associated with a reduced surface expression of CD95L upon restimulation.


METHODS
Utilizing RT-PCR, Western blotting and flow cytometry, we analyzed time-dependent changes in levels of CD95L mRNA, cytosolic protein and surface expression in five long-term human T cell clones and polarized helper populations.


RESULTS
We confirm that the inducible CD95L surface expression is lower or absent in all tested AICD-resistant clones as compared to sensitive cells. It is of interest that striking differences with respect to the activation-dependent inducibility of CD95L mRNA expression in individual resistant clones were observed. In addition, alterations in the expression of the inhibitory phosphatase FAP-1 or TCR-dependent changes in CD95 sensitivity in AICD-resistant clones could be ruled out as a mechanism for AICD resistance of human T cell clones.


CONCLUSIONS
(1) The data presented strongly support the previous notion that AICD resistance of human T cell clones is mainly regulated by a differential expression of CD95L. (2) Differential expression of CD95L on individual resistant clones results from a lack of mRNA induction in one set and from a markedly decreased surface expression of translated protein in another set of clones.
Janssen
O
O
Institute for Immunology, Christian-Albrechts University, Kiel, Germany. ojanssen@immunologie.uni-kiel.de
Stocker
A
A
Sanzenbacher
R
R
Oberg
H H
HH
Siddiqi
M A
MA
Kabelitz
D
D
D000911:Antibodies, Monoclonal / Q000633:toxicity; D017209:Apoptosis / Q000276:immunology*; D002352:Carrier Proteins / Q000276:immunology; D016764:Cell Polarity / Q000276:immunology; D002999:Clone Cells / Q000276:immunology; D018920:Coculture Techniques; D003602:Cytotoxicity, Immunologic; D053222:Fas Ligand Protein; D006801:Humans; D007113:Immunity, Innate; D019169:Jurkat Cells; D008024:Ligands; D008213:Lymphocyte Activation / Q000276:immunology*; D008562:Membrane Glycoproteins / Q000096:biosynthesis / Q000235:genetics; D054595:Protein Tyrosine Phosphatase, Non-Receptor Type 13; D017027:Protein Tyrosine Phosphatases / Q000276:immunology; D012333:RNA, Messenger / Q000096:biosynthesis; D017260:Receptor-CD3 Complex, Antigen, T-Cell / Q000276:immunology / Q000502:physiology; D016176:T-Lymphocyte Subsets / Q000201:enzymology / Q000276:immunology*; D006377:T-Lymphocytes, Helper-Inducer / Q000201:enzymology / Q000276:immunology / Q000378:metabolism; D014407:Tumor Cells, Cultured; D019014:fas Receptor / Q000276:immunology / Q000633:toxicity
D000911:Antibodies, Monoclonal; D002352:Carrier Proteins; C505661:FASLG protein, human; D053222:Fas Ligand Protein; D008024:Ligands; D008562:Membrane Glycoproteins; D012333:RNA, Messenger; D017260:Receptor-CD3 Complex, Antigen, T-Cell; D019014:fas Receptor; C516742:PTPN13 protein, human; D054595:Protein Tyrosine Phosphatase, Non-Receptor Type 13; D017027:Protein Tyrosine Phosphatases