Induction of CD4+ T cell apoptosis as a consequence of impaired cytoskeletal rearrangement in UVB-irradiated dendritic cells.
Low dose UVB irradiation of dendritic cells (DC) dose-dependently decreases their allostimulatory capacity and inhibits alloreactive T cell proliferation. The reduction of the stimulatory capacity is not associated with a perturbation of CD28 costimulation. To examine the underlying mechanism, cell cycle analysis of T cells from cocultures with UVB-irradiated DC (UVB-DC) was performed, revealing no cell cycle arrest, but an increased number of apoptotic T cells in sub-G(0) phase. We confirmed T cells to undergo apoptosis after coincubation with UVB-DC by TUNEL staining and DNA laddering. To analyze whether T cell apoptosis requires the Fas/Fas ligand (FasL) pathway, MLRs were performed with Fas-, FasL-deficient, and wild-type DC and T cells. No differences were found on comparison of wild-type DC with Fas-/FasL-deficient DC or T cells. Likewise, addition of a neutralizing anti-TNF-alpha mAb to cocultures could not overcome inhibition of T cell proliferation by UVB-DC, excluding involvement of the TNF-alpha/TNF-alphaR pathway. FACS analysis of CD69 and CD25 revealed no up-regulation on T cells cocultured with UVB-DC, suggesting a perturbation of early T cell activation. Analysis of UVB-DC by confocal microscopy demonstrated impaired filamentous actin bundling, a process critical for T cell stimulation. To investigate the functional relevance of these observations, time lapse video microscopy was performed. Indeed, calcium signaling in CD4(+) T cells was significantly diminished after interaction with UVB-DC. In conclusion, UVBR of DC impairs their cytoskeletal rearrangement and induces apoptosis in CD4(+) T cells by disruption of early DC-T cell interaction, resulting in a reduced Ca(2+) influx in T cells.
Wachter
Tina
T
Department of Dermatology, Albert-Ludwigs-Universität, Freiburg, Germany.
Averbeck
Marco
M
Hara
Hisamichi
H
Tesmann
Jens P
JP
Simon
Jan C
JC
Termeer
Christian C
CC
Denfeld
Ralf W
RW
D000818:Animals; D017209:Apoptosis / Q000276:immunology* / Q000528:radiation effects*; D018122:B7-1 Antigen / Q000494:pharmacology; D018106:CD28 Antigens / Q000494:pharmacology; D015496:CD4-Positive T-Lymphocytes / Q000166:cytology* / Q000276:immunology; D002450:Cell Communication / Q000276:immunology / Q000528:radiation effects; D002455:Cell Division / Q000276:immunology / Q000528:radiation effects; D002478:Cells, Cultured; D003599:Cytoskeleton / Q000378:metabolism* / Q000528:radiation effects*; D003713:Dendritic Cells / Q000276:immunology* / Q000378:metabolism / Q000528:radiation effects*; D004307:Dose-Response Relationship, Radiation; D053222:Fas Ligand Protein; D008024:Ligands; D008213:Lymphocyte Activation / Q000528:radiation effects; D008562:Membrane Glycoproteins / Q000502:physiology; D051379:Mice; D008807:Mice, Inbred BALB C; D008810:Mice, Inbred C57BL; D019463:Mice, Inbred MRL lpr; D008822:Mice, Transgenic; D015398:Signal Transduction / Q000276:immunology / Q000528:radiation effects; D014466:Ultraviolet Rays; D019014:fas Receptor / Q000502:physiology
D018122:B7-1 Antigen; D018106:CD28 Antigens; D053222:Fas Ligand Protein; C505658:Fasl protein, mouse; D008024:Ligands; D008562:Membrane Glycoproteins; D019014:fas Receptor