Rat Kupffer cell-derived nitric oxide modulates induction of lymphokine-activated killer cell

Regulation of lymphocytes by nitric oxide

Shortly after the identification of nitric oxide (NO) as a product of macrophages, it was discovered that NO generated by inducible NO synthase (iNOS) inhibits the proliferation of T lymphocytes. Since then, it has become clear that iNOS activity also regulates the development, differentiation, and/or function of various types of T cells and B cells and also affects NK cells. The three key mechanisms underlying the iNOS-dependent immunoregulation are (a) the modulation of signaling processes by NO, (b) the depletion of arginine, and (c) the alteration of accessory cell functions. This chapter highlights important principles of iNOS-dependent immunoregulation of lymphocytes and also reviews more recent evidence for an effect of endothelial or neuronal NO synthase in lymphocytes.

In vivo quantitative bioluminescence tomography using heterogeneous and homogeneous mouse models

Bioluminescence tomography (BLT) is a new optical molecular imaging modality, which can monitor both physiological and pathological processes by using bioluminescent light-emitting probes in small living animal. Especially, this technology possesses great potential in drug development, early detection, and therapy monitoring in preclinical settings. In the present study, we developed a dual modality BLT prototype system with Micro-computed tomography (MicroCT) registration approach, and improved the quantitative reconstruction algorithm based on adaptive hp finite element method (hp-FEM). Detailed comparisons of source reconstruction between the heterogeneous and homogeneous mouse models were performed. The models include mice with implanted luminescence source and tumor-bearing mice with firefly luciferase report gene. Our data suggest that the reconstruction based on heterogeneous mouse model is more accurate in localization and quantification than the homogeneous mouse model with appropriate optical parameters and that BLT allows super-early tumor detection in vivo based on tomographic reconstruction of heterogeneous mouse model signal.

Nitric oxide inhibits exocytosis of cytolytic granules from lymphokine-activated killer cells

NO inhibits cytotoxic T lymphocyte killing of target cells, although the precise mechanism is unknown. We hypothesized that NO decreases exocytosis of cytotoxic granules from activated lymphocytes. We now show that NO inhibits lymphokine-activated killer cell killing of K562 target cells. Exogenous and endogenous NO decreases the release of granzyme B, granzyme A, and perforin: all contents of cytotoxic granules. NO inhibits the signal transduction cascade initiated by cross-linking of the T cell receptor that leads to granule exocytosis. In particular, we found that NO decreases the expression of Ras, a critical signaling component within the exocytic pathway. Ectopic expression of Ras prevents NO inhibition of exocytosis. Our data suggest that Ras mediates NO inhibition of lymphocyte cytotoxicity and emphasize that alterations in the cellular redox state may regulate the exocytic signaling pathway.

Hepatocellular oxidative DNA injury induced by macrophage-derived nitric oxide

Previous studies have indicated that splenic macrophages migrate into the liver and play a role in endotoxin-induced hepatic damage. The present study was designed to elucidate the mechanisms of hepatocyte injury induced by activated splenic macrophages, focusing especially on endogenously released NO and oxidative DNA alterations in hepatocytes. Splenic macrophages isolated from Wistar rats were incubated with either lipopolysaccharide (LPS) or interferon-gamma (IFN-gamma) and cocultured with hepatocytes. Nitrite and nitrate levels in the culture medium were measured, and inducible-type NO synthase (iNOS) and nitrotyrosine were determined by immunofluorescence staining. The ratio of 8-hydroxy-deoxyguanosine (8-OH-dG) to deoxyguanosine (dG) was measured by high-performance liquid chromatography, and single-stranded DNA in hepatocytes was detected with acridine orange. NO release and nitrotyrosine expression in hepatocytes increased after 8 h of coculture with activated macrophages, and this coculture also induced increases in the 8-OH-dG/dG ratio and single-stranded DNA in the hepatocytes. These alterations were attenuated by superoxide dismutase (SOD) and NO synthesis inhibitors. A similar pattern of alterations was observed in hepatocytes incubated with SIN-1, and these changes were also prevented by SOD. These results suggest that activated macrophage-derived NO and its oxidative metabolite, peroxynitrite, play key roles in hepatocyte injury during inflammation, and cause subsequent DNA damage in surviving hepatocytes.