MRL/lpr CD4⁻CD8⁻ and CD8⁺ T cells, respectively, mediate Fas‐dependent and perforin cytotoxic pathways

Abstract

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.

Roles of programmed death-1 (PD-1)/PD-1 ligands pathway in the development of murine acute myocarditis caused by coxsackievirus B3

“…The primer sequences, annealing temperature, and the number of cycles for IL-2, IFN-γ, CD40L, GAPDH, FasL, PFP, and CVB3 genomes were as published elsewhere [6,[22][23][24][25]. The PCR was performed denaturation at 94°C for 1 min, primer annealing for 2 min, and primer extension at 72°C for 3 min.…”

Arsenic trioxide: a promising novel therapeutic agent for lymphoproliferative and autoimmune syndromes in MRL/lpr mice

“…The lpr mutation engenders much less expression of the Fas death receptor, which results in the accumulation, in lymph nodes (LNs) and spleens, of numerous activated DN T lymphocytes that are not normally regulated by the Fas-mediated mechanism controlling apoptosis of mature T cells. 3,4 Therefore, MRL/lpr T and B cells massively overexpress Fas ligand (FasL), which renders them able to kill Fas ϩ cells in vitro [5][6][7][8] and in vivo. [9][10][11] However, lpr mutation cannot account for the entire autoimmune syndrome of MRL/lpr mice and other genes of pathologic importance in the MRL background have been mapped.…”

The Fas - Fas Ligand apoptotic pathway

“…In the autoimmune-prone MRL/lpr mice, as a consequence of the defect in the AICD, CD4-CD8-double-negative (DN) T lymphocytes accumulating in this strain overexpress the FasL. Owing to the massive overexpression of the FasL, the DN T lymphocytes exhibited cytotoxic activity against tumor cells bearing spontaneously, or after transfection, the Fas molecule (Chu et al, 1995;Watanabe et al, 1995) or against H-2 compatible or incompatible Fas expressing thymocytes or lipopolysaccharide-induced blasts (Benihoud et al, 1997). Therefore, the overexpression of FasL by activated MRL/lpr lymphocytes could be responsible for a chronic, non-antigen-specific autoimmune attack on organs expressing low levels of the Fas receptor.…”