MRL/lpr CD4- CD8- and CD8+ T cells, respectively, mediate Fas-dependent and perforin cytotoxic pathways.
Autoimmune-prone MRL/lpr mice, homozygous for the lpr mutation, exhibit defective apoptosis and develop generalized lymphoproliferation with the accumulation of a double-negative (DN: CD4- CD8-) T cell population. The capacity of lpr T lymphocytes to effectuate Fas- and perforin-mediated cytotoxicity was investigated. Spleen and lymph nodes cells spontaneously lyse Fas- targets (thymocytes) through a Fas-mediated mechanism as a consequence of their overexpression of Fas ligand (FasL) confirmed by semiquantitative reverse transcription (RT)-PCR and immunoprecipitation analysis. This cytotoxicity was greatly increased after stimulation of the effectors by phorbol myristate acetate (PMA) + ionomycin. Under these conditions, MRL/lpr spleen and LN cells exhibited strong Fas-mediated Ca2+-independent cytotoxic activity against wild-type Fas+ (H-2 compatible or incompatible) thymocytes or lipopolysaccharide (LPS)-transformed blast cells. Such Fas-mediated cytotoxic activity was also observed with C57BL/6-lpr, but never with wild-type C57BL/6 or MLR+/+ effectors. Depletion experiments showed that the effector cells of this Fas-mediated cytotoxicity were DN T cells. This subset, which represent in vivo activated T cells, can spontaneously lyse Fas+ targets by a mechanism that does not need the interaction of the T cell receptor (TCR) with major histocompatibility complex molecule plus antigen. This lytic potential is increased by PMA + ionomycin, which sends a second activation signal to these primed T cells. Therefore, the small amounts of Fas receptor expressed on MRL/lpr tissues may account for their nonspecific autoimmune attack by DN cells. In Con A-containing medium, which allows detection of the perforin-mediated pathway against Fas targets, cytotoxic CD8+ effectors were detected that are able to kill lpr thymocytes via a Ca2+-dependent pathway. Thus, in MRL/lpr mice, these CD8+ cells could constitute potent cytotoxic effectors against cells presenting antigen to their TCR.
Benihoud
K
K
INSERM U 267, Villejuif, France.
Bonardelle
D
D
Bobé
P
P
Kiger
N
N
D000818:Animals; D015704:CD4 Antigens / Q000032:analysis*; D016827:CD8 Antigens / Q000032:analysis*; D002478:Cells, Cultured; D003208:Concanavalin A / Q000032:analysis; D003470:Culture Media / Q000737:chemistry; D003602:Cytotoxicity, Immunologic / Q000276:immunology*; D053222:Fas Ligand Protein; D015759:Ionomycin / Q000032:analysis; D008024:Ligands; D008562:Membrane Glycoproteins / Q000096:biosynthesis / Q000276:immunology*; D051379:Mice; D008810:Mice, Inbred C57BL; D008811:Mice, Inbred DBA; D019463:Mice, Inbred MRL lpr; D054353:Perforin; D052899:Pore Forming Cytotoxic Proteins; D016176:T-Lymphocyte Subsets / Q000276:immunology*; D013602:T-Lymphocytes, Cytotoxic / Q000276:immunology* / Q000378:metabolism; D013755:Tetradecanoylphorbol Acetate / Q000032:analysis; D019014:fas Receptor / Q000276:immunology*
D015704:CD4 Antigens; D016827:CD8 Antigens; D003470:Culture Media; D053222:Fas Ligand Protein; C505658:Fasl protein, mouse; D008024:Ligands; D008562:Membrane Glycoproteins; D052899:Pore Forming Cytotoxic Proteins; D019014:fas Receptor; D003208:Concanavalin A; D054353:Perforin; D015759:Ionomycin; D013755:Tetradecanoylphorbol Acetate