The role of interleukin-2 in regulating the sensitivity of natural killer cells for Fas-mediated apoptosis.
The Fas/Fas-ligand (FasL) system seems to play a key role in regulating immunoresponses. Highly purified CD56+CD3- natural killer (NK) cells were found to be resistant to the apoptosis-inducing Fas mAb CH11 in the absence or in the presence of interleukin-2 (IL-2) for up to 3 days. However, NK cells activated with IL-2 for 3 days became apoptotic following combined treatment with CH11 and actinomycin D, suggesting the presence of an intact apoptotic machinery. In contrast, NK cells cultivated in IL-2 for 6 days became sensitive to CH11-induced apoptosis without addition of actinomycin D. At this time, a pronounced up-regulation of the Fas protein on the NK cell membrane was detected. By using reverse transcription/polymerase chain reaction it was found that the anti-apoptotic gene FLIP was strongly expressed in NK cells for up to 6 days of IL-2 stimulation. After day 6, a time-dependent decrease in the expression of FLIP was observed concomitantly with increased sensitivity for Fas-mediated apoptosis. The amount of apoptotic and necrotic NK cells in the presence of IL-2 increased in a time-dependent manner, reaching 40% at day 6 of culture. The amount of apoptotic and necrotic NK cells was reduced in the presence of Fas-Fc protein. In addition, IL-2 stimulated the NK cells to release soluble FasL in a time-dependent manner, whereas membrane FasL did not seem to increase in a similar manner. These results indicate that Fas/FasL interactions are involved in the down-regulation of IL-2-activated human NK cells.
Institute of Cancer Research and Molecular Biology, Norwegian University of Science and Technology, Trondheim. Johan.Haux@medisin.ntnu.no
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Haux
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Johnsen
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Steinkjer
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Egeberg
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Sundan
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Espevik
D016475:3T3 Cells; D000818:Animals; D000911:Antibodies, Monoclonal / Q000276:immunology; D017209:Apoptosis; D053446:CASP8 and FADD-Like Apoptosis Regulating Protein; D002352:Carrier Proteins / Q000032:analysis; D003609:Dactinomycin / Q000494:pharmacology; D053222:Fas Ligand Protein; D006801:Humans; D016219:Immunotherapy, Adoptive; D007376:Interleukin-2 / Q000494:pharmacology*; D047908:Intracellular Signaling Peptides and Proteins; D007694:Killer Cells, Natural / Q000187:drug effects* / Q000502:physiology; D008562:Membrane Glycoproteins / Q000032:analysis / Q000096:biosynthesis; D051379:Mice; D019014:fas Receptor / Q000032:analysis / Q000502:physiology*
D000911:Antibodies, Monoclonal; D053446:CASP8 and FADD-Like Apoptosis Regulating Protein; C506386:CFLAR protein, human; D002352:Carrier Proteins; C506387:Cflar protein, mouse; C505661:FASLG protein, human; D053222:Fas Ligand Protein; C505658:Fasl protein, mouse; D007376:Interleukin-2; D047908:Intracellular Signaling Peptides and Proteins; D008562:Membrane Glycoproteins; D019014:fas Receptor; D003609:Dactinomycin