Human purified protein derivative-specific CD4+ T cells use both CD95-dependent and CD95-independent cytolytic mechanisms.
CTL, both CD4+ and CD8+, are essential in the eradication of intracellular pathogens. Data generated using murine T cells have suggested a critical role for CD95 (Fas, Apo-1) in CD4+ T cell-induced apoptosis of target cells. In contrast, CD8+ CTL predominantly use the perforin/granzyme lytic pathway. At present little is known about the mechanism of CD4+ CTL lytic function during intracellular infection in humans. We have used human CD4+ T cells specific for purified protein derivative (PPD) of Mycobacterium tuberculosis to explore whether CD95 is the dominant cytolytic mechanism. PPD-reactive CD4+ clones efficiently lysed Ag-pulsed autologous monocytes, adherent macrophages, and EBV-transformed B cells. Addition of an antagonistic CD95 Ab had a minimal effect on cytolysis, whereas addition of MgEGTA to block perforin/granzyme resulted in complete inhibition of killing. In contrast, lysis of activated peripheral blood B cells could be partially blocked with the antagonistic CD95 Ab. Supporting these observations, monocytes, macrophages, and EBV-transformed B cells were not lysed by an agonistic CD95 Ab. Activated B cells were readily lysed by the agonistic CD95 Ab. T cell clones triggered through the TCR with anti-CD3 were capable of lysing the CD95-sensitive Jurkat T cell line in a CD95-dependent manner, but were also able to release granzymes. We conclude that human CD4+ T cells are capable of lysing PPD-pulsed targets using both perforin/granzyme and CD95 pathways. The contribution of CD95 is strictly dependent on target cell susceptibility to CD95-mediated killing.
Lewinsohn
D M
DM
Division of Pulmonary and Critical Care Medicine, University of Washington, Seattle 98195, USA.
Bement
T T
TT
Xu
J
J
Lynch
D H
DH
Grabstein
K H
KH
Reed
S G
SG
Alderson
M R
MR
D019138:Antibodies, Blocking / Q000494:pharmacology; D015496:CD4-Positive T-Lymphocytes / Q000201:enzymology / Q000276:immunology*; D002460:Cell Line; D002999:Clone Cells; D003601:Cytotoxicity Tests, Immunologic; D003602:Cytotoxicity, Immunologic; D000939:Epitopes / Q000276:immunology; D004950:Esterases / Q000378:metabolism; D053222:Fas Ligand Protein; D006801:Humans; D019169:Jurkat Cells; D008213:Lymphocyte Activation / Q000235:genetics; D008264:Macrophages / Q000276:immunology; D008562:Membrane Glycoproteins / Q000235:genetics; D009000:Monocytes / Q000276:immunology; D054353:Perforin; D052899:Pore Forming Cytotoxic Proteins; D012333:RNA, Messenger / Q000096:biosynthesis; D013602:T-Lymphocytes, Cytotoxic / Q000201:enzymology / Q000276:immunology*; D014373:Tuberculin / Q000276:immunology*; D019014:fas Receptor / Q000096:biosynthesis / Q000276:immunology / Q000502:physiology*
D019138:Antibodies, Blocking; D000939:Epitopes; C505661:FASLG protein, human; D053222:Fas Ligand Protein; D008562:Membrane Glycoproteins; D052899:Pore Forming Cytotoxic Proteins; D012333:RNA, Messenger; D014373:Tuberculin; D019014:fas Receptor; D054353:Perforin; D004950:Esterases; C022635:serine esterase