Graft-versus-host-disease-associated lymphoid hypoplasia and B cell dysfunction is dependent upon donor T cell-mediated Fas-ligand function, but not perforin function

Induction of Fas Ligand in Murine Bone Marrow NK Cells by Bacterial Polysaccharides

Bacterial polysaccharides have a wide range of activities in mammals. We have studied the effect of LPS and poly-β-(1→4)-d-mannuronate (mannuronan, poly-M), an exopolysaccharide from Pseudomonas aeruginosa, on the cytotoxicity mediated by murine bone marrow cells (BMC). Addition of LPS or mannuronan to BMC induced a time- and dose-dependent cytotoxicity against Jurkat cells. The LPS- or mannuronan-induced cytotoxicity was due to increased Fas ligand (FasL) expression by BMC, since 1) Fas-transfected L1210-Fas target cells were more susceptible to lysis than the Faslow-expressing parent L1210 cells, 2) stimulated BMC from FasL-defective gld/gld mice were not cytolytic and, 3) the cytolytic activity of normal BMC was inhibited by a Fas-Fc fusion protein. Flow cytometry showed an increase in surface FasL in LPS-stimulated BMC. RT-PCR analysis of BMC revealed constitutive expression of FasL mRNA, which was increased after LPS stimulation. Immunomagnetic depletion of NK1.1-, CD2-, or CD32/16-expressing cells from BMC abrogated the LPS-induced BMC cytotoxicity against L1210-Fas cells, suggesting that NK cells were the cytotoxic effector cells. Depletion of CD45R/B220-, Gr-1-, or CD11b/Mac-1-expressing cells only partially decreased BMC-mediated cytotoxicity, and depletion of CD4- or CD8a-expressing cells had no effect. The results support the conclusion that LPS and mannuronan induce expression of cytotoxic FasL on bone marrow NK cells.

Dual mechanisms of apoptosis induction by cytotoxic lymphocytes

Cytotoxic T lymphocytes and natural killer cells together comprise the means by which the immune system detects and rids higher organisms of virus-infected or transformed cells. Although differing considerably in the way they detect foreign or mutated antigens, these cells utilize highly analogous mechanisms for inducing target cell death. Both types of effector lymphocytes utilize two principal contact-dependent cytolytic mechanisms. The first of these, the granule exocytosis mechanism, depends on the synergy of a calcium-dependent pore-forming protein, perforin, and a battery of proteases (granzymes), and it results in penetration by effector molecules into the target cell cytoplasm and nucleus. The second, which requires binding of FasL (CD95L) on the effector cell with trimeric Fas (CD95) molecules on receptive target cells, is calcium independent and functions by generating a death signal at the inner leaflet of the target cell membrane. Exciting recent developments have indicated that both cytolytic mechanisms impinge on an endogenous signaling pathway that is strongly conserved in species as diverse as helminths and humans and dictates the death or survival of all cells.

CD4+ and CD8+ T cells each can utilize a perforin-dependent pathway to mediate lethal graft-versus-host disease in major histocompatibility complex-disparate recipients

Perforin-deficient (-/-) mice were used as T-cell donors for infusion into irradiated major histocompatibility complex (MHC)-disparate recipients to investigate the requirement for perforin-mediated cytolysis during graft-versus-host disease (GVHD) generation. Administration of 5x10(6) C57BL/6 (H2b) perforin -/- splenocytes was significantly less effective in inducing GVHD lethality when given to MHC class I + II disparate B10.BR (H2k) recipients, as compared with wild-type (+/+) controls. Perforin expression by donor T cells was not required for GVHD induction because recipients given fivefold higher numbers of perforin -/- donor splenocytes uniformly succumbed to lethal GVHD. Because both CD4+ and CD8+ donor T cells are required for optimal GVHD lethality in this strain combination, to discern the relative contribution of perforin-mediated cytolysis by CD4+ and CD8+ T cells, additional studies were performed. For these latter studies, we used a sensitive assay involving the infusion of highly purified CD4+ or CD8+ T cells into sublethally irradiated MHC class II or I disparate recipients, respectively. As compared with recipients of perforin +/+ T cells, recipients of either CD4+ or CD8+ perforin -/- T-cell subsets had a significant reduction in GVHD-mediated lethality at T-cell doses that were uniformly lethal. T-cell dose titration studies established that GVHD lethality in recipients of perforin -/- CD4+ or CD8+ T cells was reduced by approximately threefold. These data are the first to indicate that approaches to limit perforin-mediated cytolysis should be similarly effective in situations in which CD4+ or CD8+ T cells dominate the GVHD response.

A Metalloproteinase Inhibitor Prevents Lethal Acute Graft-Versus-Host Disease in Mice

Tumor necrosis factor (TNF ) and Fas ligand (FasL) have been implicated in the pathogenesis of graft-versus-host disease (GVHD), which is a major complication after allogeneic bone marrow transplantation. We examined here the ameliorating effect of a metalloproteinase inhibitor (KB-R7785) that inhibits TNF-α and FasL release in a lethal acute GVHD model in mice. Administration of KB-R7785 into (BALB/c × C57BL/6) F1 that received C57BL/6 spleen cells markedly reduced the mortality and weight loss in association with minimal signs of GVHD pathology in the liver, intestine, and hematopoietic tissues. The ameliorating effect of KB-R7785 was superior to that of anti–TNF-α antibody. Our results suggest that KB-R7785 could be a potent therapeutic agent for GVHD.

A Metalloproteinase Inhibitor Prevents Lethal Acute Graft-Versus-Host Disease in Mice

Tumor necrosis factor (TNF ) and Fas ligand (FasL) have been implicated in the pathogenesis of graft-versus-host disease (GVHD), which is a major complication after allogeneic bone marrow transplantation. We examined here the ameliorating effect of a metalloproteinase inhibitor (KB-R7785) that inhibits TNF-α and FasL release in a lethal acute GVHD model in mice. Administration of KB-R7785 into (BALB/c × C57BL/6) F1 that received C57BL/6 spleen cells markedly reduced the mortality and weight loss in association with minimal signs of GVHD pathology in the liver, intestine, and hematopoietic tissues. The ameliorating effect of KB-R7785 was superior to that of anti–TNF-α antibody. Our results suggest that KB-R7785 could be a potent therapeutic agent for GVHD.