CD4 T lymphocytes are primed to express Fas ligand by CD4 cross-linking and to contribute to CD8 T-cell apoptosis via Fas/FasL death signaling pathway.
CD4 molecules serve as coreceptors for the T-cell receptor (TCR)/CD3 complex that are engaged coordinately with TCR and facilitate antigen-specific T-cell activation leading to interleukin 2 (IL-2) production and proliferation. However, cross-ligation of CD4 molecules prior to TCR stimulation has been shown to prime CD4 T cells to undergo apoptosis. Although in vivo and in vitro experiments have implicated the involvement of Fas/FasL interaction in this CD4 cross-linking (CD4XL)-induced apoptosis, detailed mechanisms to account for cell death induction have not been elucidated. In the present study, we demonstrate that CD4XL in purified T cells not only led to Fas up-regulation but also primed CD4 T cells to express FasL upon CD3 stimulation and rendered the T cells susceptible to Fas-mediated apoptosis. Notably, in addition to CD4(+) T cells, CD4XL-induced sensitization for apoptosis was observed in CD8(+) T cells as well and was associated with Bcl-x down-modulation. Both CD4 and CD8 T-cell subsets underwent apoptosis following cell-cell contact with FasL(+) CD4 T cells. CD28 costimulation abrogated CD4XL/CD3-induced apoptosis with restoration of IL-2 production and prevented Bcl-x down-modulation. As CD4 molecules are the primary receptors for human immunodeficiency virus 1 (HIV-1), we conclude that HIV-1 envelope mediated CD4XL can lead to the generation of FasL-expressing CD4(+) T cells that can lead to apoptosis of CD4 as well as CD8 T cells. These findings implicate a novel mechanism for CD8 T-cell depletion in HIV disease.
Tateyama
M
M
Department of Pediatrics, Division of Allergy/Immunology, North Shore University Hospital-New York University School of Medicine, Manhasset, New York 11030, USA.
Oyaizu
N
N
McCloskey
T W
TW
Than
S
S
Pahwa
S
S
D015703:Antigens, CD / Q000276:immunology; D017209:Apoptosis / Q000276:immunology*; D017252:CD3 Complex / Q000276:immunology; D015704:CD4 Antigens / Q000276:immunology*; D015496:CD4-Positive T-Lymphocytes / Q000276:immunology* / Q000502:physiology; D018414:CD8-Positive T-Lymphocytes / Q000166:cytology / Q000276:immunology* / Q000502:physiology; D053222:Fas Ligand Protein; D006801:Humans; D007371:Interferon-gamma / Q000096:biosynthesis; D008213:Lymphocyte Activation; D008562:Membrane Glycoproteins / Q000235:genetics / Q000276:immunology*; D012333:RNA, Messenger / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction / Q000276:immunology*; D014409:Tumor Necrosis Factor-alpha / Q000096:biosynthesis; D019014:fas Receptor / Q000276:immunology*
D015703:Antigens, CD; D017252:CD3 Complex; D015704:CD4 Antigens; C505661:FASLG protein, human; D053222:Fas Ligand Protein; D008562:Membrane Glycoproteins; D012333:RNA, Messenger; D014409:Tumor Necrosis Factor-alpha; D019014:fas Receptor; D007371:Interferon-gamma