Neutrophil apoptosis and hypoxia.

Neutrophils are the most abundant population of leukocytes, which constitute the defense against pathogens. Released by neutrophils the proteolytic enzymes and reactive oxygen species help in eliminating infections, but also cause extensive tissue damage. Neutrophil apoptosis plays an essential role in cell homeostasis and resolution of inflammation. It is mediated by a complex network of intracellular apoptotic/survival signaling pathways and can be modulated by a variety of extracellular stimuli such as hypoxia. Here, we review recent studies on the mechanisms of neutrophil death and survival accentuating on neutrophil apoptosis under hypoxic conditions. Neutrophils possess components of both extrinsic and intrinsic apoptotic routes. However in neutrophils this mechanism has special features. The involvement of death receptors, caspases, mitochondria, and Bcl-2 proteins are discussed. Both the transcription factor NF-kappaB and p38MAPK regulate the neutrophil apoptotic program. Despite that reactive oxygen species (ROS) can directly promote and/or adjust apoptosis, there is no consensus about the role of ROS on neutrophil lifespan. Thus both the type of ROS involved and the site of their generation may be important for neutrophil apoptosis. Finally, hypoxia can activate several signaling pathways. The possible differences between the effects of sustained and intermittent hypoxia are also addressed.

Activated CD8+ T-lymphocytes in obstructive sleep apnoea.

T-lymphocytes are implicated in the development of atherosclerosis. The aim of this study was to assess whether the CD8+ T-lymphocytes of obstructive sleep apnoea (OSA) patients undergo phenotypic and functional changes that may exaggerate atherogenic sequelae in OSA. A total of 36 OSA patients, 17 controls and 15 single-night-treated OSA patients were studied. Phenotype and cytotoxicity against K562 target cells were analysed by flow cytometry. Cytotoxicity against human umbilical vein endothelial cells (HUVECs) was assessed by 51Cr release assay. The cytotoxicity of the CD8+ T-lymphocytes of OSA patients against K562 and HUVECs was significantly greater than controls. This increased cytotoxicity directly depended on the presence of perforin and natural killer receptors (CD56, CD16), which were significantly increased in OSA CD8+ T-lymphocytes. Also the percentage of the CD56bright subset, which mediates initial interactions with vascular endothelium, significantly increased in OSA. Nasal continuous positive airway pressure treatment significantly decreased CD8+ T-cell cytotoxicity and CD56 expression, and was positively correlated with natural killer inhibitory NKB1 receptor expression either after a single-night treatment or after a prolonged treatment. In conclusion, the CD8+ T-lymphocytes of obstructive sleep apnoea patients undergo phenotypic and functional changes, rendering them cytotoxic to target cells via increased CD56+/perforin+ expression, which can be ameliorated by nasal continuous positive airway pressure treatment. These results are compatible with the current authors' hypothesis of atherogenic sequelae in obstructive sleep apnoea.

Immune potential of lymph node-derived lymphocytes in uncontrolled hemorrhagic shock.

The state of T cell immunity was evaluated in rats in early (1-4 h) hemorrhagic shock induced by a massive splenic injury. T cell subpopulations from treated and untreated shocked animals were tested by flow cytometry and the results were compared with healthy controls. A fall in CD4+ T lymphocyte and natural killer (NKR-P1+) cell number, marked decline in the T helper (CD4+) to T suppressor (CD8+) ratio, and decrease of interleukin-2 receptor (IL-2R) bearing cells in peripheral blood, mesenteric, and popliteal lymph nodes of rats was found in the early stages of hemorrhagic shock. The same phenotype profile was also revealed in lymphocytes of rats in hemorrhagic shock following massive splenic injury treated with Ringer's lactate. The number of TCRalpha beta and TCR-gamma delta positive cells, as well as the percentage of CD4 and CD8 positive cells in the thymus, was similar in all groups of rats. Culture of lymph node cells taken from rats following hemorrhage in the presence of 100 U/mL hrIL-2 resulted in a marked increase in the number of NKR-PI+ positive cells from 4.2% to 30.5% (P < 0.001). Magnet separated NKR-P1+ fractions lysed the allogeneic fibroblasts in the same manner as IL-2-activated NKR-P1 cells from the control rats. Popliteal lymph node (PLNi) CD8b+ lymphocytes from rats in hemorrhagic shock preinfected into the footpad with cytomegalovirus (CMV) 6 days prior to injury lost their ability to lyse the CMV-infected fibroblasts and protect the monolayer from CMV infection when compared with PLNi cells from control infected rats. The possible mechanisms for the observed cellular dysfunction following hemorrhage are discussed.

Cure of fibroblast monolayers from murine cytomegalovirus infection: phenotypic assessment of rat lymphoid cell population developed on fibroblast monolayers.

Rat and mouse fibroblast monolayers were infected with murine cytomegalovirus (MCMV) by 2 hr incubation to allow virus to penetrate the cells. Then lymph node cells (LNC) from rats infected with MCMV and from untreated rats were added together with human recombinant interleukin-2 (hrIL-2). Cytopathic plaques appeared within 2-3 days. In culture of fibroblasts only, 30-40 plaques per well progressed into confluent cytopathy within 6-8 days. In cultures with LNC syngeneic to fibroblasts, plaques appeared; however, the cytotoxic T lymphocyte population that developed and specific apoptotic fragmentation eliminated the cytomegalic cells in the plaques. The surrounding cells stretched to the area, the cytopathic plaques disappeared, and the monolayer resumed its uninfected texture. No plaque-forming units could be isolated from such cured cultures. In allogeneic combination there was no apoptotic target cell killing. However, in cultures stimulated by hrIL-2, plaque growth was arrested and the plaques remained rudimentary. Similarly, arrest of plaques was also obtained in cultures containing LNC from uninfected rats, but only if stimulated by hrIL-2. In mouse fibroblasts carrying the rat LNC, plaque growth was not arrested, and the culture developed into confluent cytopathy. Interferon (IFN)-gamma or -alpha,beta added 24 hr before and 2 hr after infection abolished plaque appearance or arrested growth. IFN-gamma appeared to be the most effective. Fluids harvested from cured cultures also protected from plaque development. Antibodies to IFN-gamma, but not to IFN-alpha,beta, neutralized this capacity in the culture fluids. It is concluded that IFN-gamma produced by the LNC played a major role in the cure of the fibroblast culture from MCMV infection. A mechanism of cell-mediated immunity operating in resolving virus infection is proposed.

Characterisation of the morphogenetic course and secretion of two different types of mucoid material by granulated metrial gland/lymphokine-activated killer cells.

Lymphocytes from mesenteric lymph nodes of ordinary and nude mice were grown in microtitre wells on embryonic mesenchymal-fibroblast monolayers. Human recombinant interleukin-2 (80 units ml-1) was added. Clones of lymphokine-activated killer (LAK) cells developed. The incidence of clone-forming cells was 52-136 per 10(5) cells in lymph nodes from nude mice and 4.2-8.3 per 10(5) cells in lymph nodes from ordinary mice. On a limited number of fibroblast monolayers propagated in culture, the maturing LAK cells were induced to synthesise and secrete 2 types of flowing mucoid material. After methanol fixation and Alcian blue/periodic acid-Schiff (PAS) (at pH 1) staining, the first type of material was distinctively stained turquoise, indicating a highly sulphated proteoglycan, chondroitin sulphate; the second type of material, a macromolecular neutral polysaccharide, was not stained and appeared to have been dissolved. Glycogen was stained deep brilliant purple. After treatment with PAS alone, the chondroitin sulphate was not stained and appeared as a bright area, the neutral polysaccharide mass being stained deep red. This polysaccharide material was characteristically secreted as droplets or 'streamlets' emerging from the cell surface and extending through the first type of material to coalesce with the already accumulated main extracellular mucoid layer spreading between the cells. Clones of secretory LAK cells were obtained from gravid and nongravid mouse uteri as well as from tracheal explants. Change of medium or passage with fresh medium to a new inducing batch of monolayer, at the blastoid-large granular lymphocyte stage (on d 3 to 7), was critical for high reproducibility of secretion. The course of differentiation was found ultimately to be dependent on the embryonic mesenchymal monolayer, suggesting induction by a morphogenetic signal. A correlation can be drawn between the secretory activity and the morphological profile at maturation of highly distinctive organised cells.

Suppression of IgE-antibody production by non-polypeptide dialysable thymic factor.

The effect of dialysable thymic extract on the IgE-antibody production in rats was studied. A marked suppression of IgE-antibody production determined by mast cell degranulation and passive cutaneous anaphylaxis tests was found in the immunized rats injected with dialysable thymic extract. The treatment of this preparation with immobilized pronase affects neither its suppressive activity, nor does such treatment affect the activity of purified factor, isolated from the crude extract. The prolonged administration of purified preparation to rats leads to an increase in thymus weight. When syngeneic thymocytes incubated with purified non-polypeptide thymic factor were administered to immunized rats a significant suppression of IgE-antibody production was observed compared to that occurring in untreated ones. On this basis, it was concluded that a decrease of IgE-antibody production may be due to a direct stimulation of T-suppressor cells.