Reactive oxygen species selectively deplete normal T lymphocytes via a hydroxyl radical dependent mechanism

Differential effect of intermittent hypoxia and sleep fragmentation on PD-1/PD-L1 upregulation

Immunosurveillance is compromised in patients with obstructive sleep apnea (OSA) as reflected by overexpression of the programmed death cell receptor and its ligand (PD-1/PD-L1) coinhibitory axis. However, the contributions of intermittent hypoxia (IH) and sleep fragmentation (SF) are unclear. We therefore evaluated the expression of PD-1 and PD-L1 on immune cells from mice subjected to IH or SF, and in human cells exposed to IH, oxidative stress, or both conditions. Six-week-old male C57BL/6J mice were exposed to either IH or SF using previously established in vivo models. Moreover, human peripheral blood mononuclear cells (PBMC) were cultured overnight under normoxia, IH, hydrogen peroxide (H2O2), or both. Murine splenocytes and human PBMC were isolated, and labeled using surface-specific antibodies for flow cytometry analysis. Compared to control mice, IH induced higher expression of PD-L1 on F4/80 cells and of PD-1 on CD4+ and CD8+ T-cells, whereas no significant changes emerged after SF. In vitro models of IH and oxidative stress showed similar changes for expression of PD-L1 on human monocytes and PD-1 on CD4+ T-cells. Furthermore, H2O2 increased PD-1 expression on CD8+ T-cells, compromising their cytotoxic capacity assessed by perforin expression, similar to IH. No evidence of synergistic effects was apparent. Therefore, PD-1/PD-L1 upregulation reported in patients with OSA appears to be preferentially mediated by IH rather than SF.

NADPH oxidase 4 expression in the normal endometrium and in endometrial cancer

The aim of this study was to explore the role of NOX4 in the biology of the normal endometrium and endometrial cancer. NOX4 plays a key role in other adenocarcinomas and has been implicated in the pathogenesis of diabetes and obesity, which are important risk factors for endometrial cancer. NOX4 expression was assessed in 239 endometrial cancer and 25 normal endometrium samples by quantitative real-time polymerase chain reaction, in situ hybridization, and immunohistochemistry. DNA methylation of the NOX4 promoter was determined by means of MethyLight PCR. Data were correlated with clinicopathological parameters and analyzed in the context of diabetes and body mass index. In the normal endometrium, NOX4 microRNA expression was significantly higher in the secretory transformed compared with proliferative endometrium ( p = 0.008). In endometrial cancer specimens, NOX4 expression did not differ between diabetic and non-diabetic patients, but was the highest in patients with a body mass index ≤ 26 ( p = 0.037). The lowest NOX4 expression was found in carcinosarcomas ( p = 0.007). High NOX4 expression predicted poorer clinical outcome with regard to overall survival, especially in non-diabetic patients and those with a body mass index > 20. Independent prognostic significance of NOX4 transcripts was retained in type I endometrial cancer and was the most meaningful in patients with a body mass index > 20. No prognostic impact was shown for NOX4 promoter methylation in endometrial cancer. For the first time, we demonstrate that NOX4 plays a considerable role in the cycle-dependent changes in the normal endometrium and in the biology of endometrial cancer.

Acute and potentially persistent effects of scuba diving on the blood transcriptome of experienced divers

During scuba diving, the circulatory system is stressed by an elevated partial pressure of oxygen while the diver is submerged and by decompression-induced gas bubbles on ascent to the surface. This diving-induced stress may trigger decompression illness, but the majority of dives are asymptomatic. In this study we have mapped divers' blood transcriptomes with the aim of identifying genes, biological pathways, and cell types perturbed by the physiological stress in asymptomatic scuba diving. Ten experienced divers abstained from diving for >2 wk before performing a 3-day series of daily dives to 18 m depth for 47 min while breathing compressed air. Blood for microarray analysis was collected before and immediately after the first and last dives, and 10 matched nondivers provided controls for predive stationary transcriptomes. MetaCore GeneGo analysis of the predive samples identified stationary upregulation of genes associated with apoptosis, inflammation, and innate immune responses in the divers, most significantly involving genes in the TNFR1 pathway of caspase-dependent apoptosis, HSP60/HSP70 signaling via TLR4, and NF-κB-mediated transcription. Diving caused pronounced shifts in transcription patterns characteristic of specific leukocytes, with downregulation of genes expressed by CD8+ T lymphocytes and NK cells and upregulation of genes expressed by neutrophils, monocytes, and macrophages. Antioxidant genes were upregulated. Similar transient responses were observed after the first and last dive. The results indicate that sublethal oxidative stress elicits the myeloid innate immune system in scuba diving and that extensive diving may cause persistent change in pathways controlling apoptosis, inflammation, and innate immune responses.

Hypoxic tumors and their effect on immune cells and cancer therapy

The abnormal decrease or the lack of oxygen supply to cells and tissues is called hypoxia. This condition is commonly seen in various diseases such as rheumatoid arthritis and atherosclerosis, also in solid cancers. Pre-clinical and clinical studies have shown that hypoxic cancers are extremely aggressive, resistant to standard therapies (chemotherapy and radiotherapy), and thus very difficult to eradicate. Hypoxia affects both the tumor and the immune cells via various pathways. This review summarizes the most common effects of hypoxia on immune cells that play a key role in the anti-tumor response, the limitation of current therapies, and the potential solutions that were developed for hypoxic malignancies.

Effects of in-vivo generation of oxygen free radicals on immune responsiveness in rabbits

Oxygen free radicals (OFRs) generated during biological processes are reportedly involved in the pathogenesis of several disease states and various reports have indicated that oxidative stress may alter immune competence. Hence, effects of in-vivo generation of OFRs by using xanthine/xanthine oxidase (X/XO) system on immune responsiveness were evaluated in rabbits. Intravenous injections of xanthine (0.14 mg/kg) along with xanthine oxidase (2 U/Kg) following primary and secondary immunizations of animals with sheep red blood cells (SRBC) significantly attenuated the primary and secondary antibody responses respectively. In tests for cell-mediated immunity, tuberculin sensitivity and leucocyte migration inhibition were also decreased significantly in sensitized animals following X/XO treatment. The observed changes in both humoral and cell-mediated immune responses following such in-vivo generation of OFRs indicate a possible nexus between OFR generation and immune suppression.

Activation of murine macrophages by hydrogen peroxide

Hydrogen peroxide at concentrations from 0.1 to 20 microM enhances phagocytosis and oxidative burst of murine peritoneal macrophages. The activation of these macrophage functions is paralleled by prolonged hyperpolarization and a transient increase in cytoplasmic free calcium concentration. All the effects are dose- and time-dependent. The results obtained for H2O2 are compared with those for a natural activator, peptide N-formyl-methionyl-leucyl-phenylalanine. The data demonstrate the ability of small doses of hydrogen peroxide to stimulate macrophages through the intracellular mechanisms of ion transduction.

Vitamin, trace element and peroxide status in HIV seropositive patients: asymptomatic patients present a severe beta-carotene deficiency

We have investigated whether nutritional status and peroxidation process are associated with the degree of development of HIV infection. This was done by measuring the status of vitamins (E, A and beta-carotene), of antioxidant trace elements (zinc, selenium) and lipid peroxide levels (lipid hydroperoxides and thiobarbituric acid reactants) in HIV-seropositive patients at CDC II and CDC IV stages and in comparison with normal subjects. There was a decrease in vitamin and trace element levels related to the severity of disease. The most dramatic decrease, however, was seen for carotenoids (0.94 +/- 0.46 mumol/l) and beta-carotene (0.24 +/- 0.14 mumol/l vs. 0.56 +/- 0.29 mumol/l) whose stage II levels were only half the normal value. Paradoxically, lipid peroxidation was higher at stage II than at stage IV. This can be attributed to an overproduction of oxygen radicals by polymorphonuclears in stage II. This deficiency in antioxidant status, often found in patients suffering from peroxidative diseases, may have important consequences on cellular immunity. Furthermore, the concomitant overproduction of free radicals may also affect HIV multiplication.

Antioxidant defenses in the bile duct-ligated rat

Changes in pro-oxidant and antioxidant balance in the serum and liver were studied in an experimental model of obstructive jaundice in the rat. The results showed a decrease in plasma vitamin E concentration (P < 0.01) and a threefold reduction in liver vitamin E concentration (P < 0.001). There was also a threefold reduction in levels of the liver enzymes glutathione peroxidase (P < 0.01) and glutathione transferase (P < 0.001), together with a six-fold reduction in catalase activity (P < 0.001). The serum selenium level decreased by 35% in the jaundiced rats (P < 0.05). The total liver glutathione level decreased to half the control value (P < 0.01). The malonyldialdehyde level, the measure of lipid peroxidation used in this study, doubled (P < 0.01). The results suggest a shift in the pro-oxidant/antioxidant balance in favor of lipid peroxidation. The possible etiology of this change and its relationship to human cholestasis are discussed.

Absence of a specific effect of free radicals on HLA-B27

The spondylitis associated HLA-B27 epitope includes a characteristic unpaired cysteine at amino acid position 67. On some B27 molecules the thiol (-SH) side chain of this residue seems to be available for chemical interactions. The possibility that free radicals produced during inflammation might specifically affect this group was investigated in this work. Cells bearing HLA-B27 were exposed to free radicals generated by ultraviolet irradiation or hydrogen peroxide, and HLA antigens were then measured by flow cytometry. Binding of monoclonal antibodies to B27 was not affected. These results do not support a specific susceptibility of HLA-B27 to damage by free radicals, despite its apparently vulnerable structure.

Analysis of free radical damage within single cells using flow cytometry

The data presented here illustrates the additional information that can be gained on single cell biological effects by using a method of damage estimation based on single cells. The experiments involving primarily free radical damage carried out using H2O2 and the radioprotectors cysteamine and WR 1065, both revealed data that could not have been obtained from a macroscopic study of free radical-DNA chemistry and analysis of reaction products. This serves to emphasise the difficulty in extrapolating both free radical based and other chemical reactions to effects seen in living systems.

Inhibition of mitogen-activated proliferation of human lymphocytes by hypochlorous acid in vitro: protection and reversal by ascorbate and cysteine

Hypochlorous acid (HOCl) at concentrations of 6.25 microM and greater caused statistically significant, dose-related inhibition of mitogen-activated proliferation of human mononuclear leucocytes (MNL). The anti-proliferative effects of HOCl, which were evident using both undepleted and adherent-cell depleted MNL, could not be attributed to decreased mitogen binding by HOCl-treated cells. The anti-oxidants ascorbate and cysteine (50 microM), when added to MNL prior to exposure to HOCl (25 microM), prevented the anti-proliferative effects of the oxidising agent. Likewise reversal of oxidant-mediated inhibition of the responsiveness of MNL to mitogens was observed when ascorbate and cysteine were added after HOCl treatment of the cells. These results suggest that HOCl, derived from activated phagocytes, is a potential mediator of immunosuppression, especially in the setting of abnormal host anti-oxidant defences.

Dithranol-mediated, dose-dependent priming and activation of luminol-enhanced chemiluminescence responses of human neutrophils in vitro

At concentrations of 10 micrograms/ml and greater, dithranol (anthralin) caused an intense, dose-related activation of luminol-enhanced chemiluminescence (LECL) of human neutrophils and also increased oxygen consumption by these cells. Activation of LECL, which was maximal with 40 micrograms/ml dithranol, occurred promptly, peaked at 3-5 min, then declined. Dithranol-mediated stimulation of LECL was inhibited by catalase and by the protein kinase C inhibitor, H-7. Neutrophils from individuals with chronic granulomatous disease were unresponsive to the pro-oxidative effects of dithranol. At concentrations of 2.5 micrograms/ml and less, dithranol did not directly activate the LECL responses of neutrophils. However pre-treatment of neutrophils with dithranol at concentrations of 0.5-2.5 micrograms/ml increased the LECL-responses of cells subsequently stimulated with calcium ionophore and opsonized zymosan. These observations demonstrate two distinct dose-related, pro-oxidative interactions of dithranol with human neutrophils: low-dose priming and high-dose activation of oxidant generation. Since phagocyte-derived reactive oxidants are immunosuppressive, these pro-oxidative interactions of dithranol with human neutrophils may contribute to the pharmacotherapeutic mechanisms of this agent.

Effect of hemodialysis on T lymphocyte subsets, con-A-activated suppressor cell activity, and interleukin-2 receptor expression on lymphocytes in chronic uremic patients

Effect of hemodialysis (HD) on some indices of immune response was studied in nine chronic uremics. Total lymphocyte, OKT4+, and OKT8+ cell numbers significantly decreased during the first 20 min of HD, and they were decreased till the third hour of the procedure, whereas the OKT4+/OKT8+ cell number ratio did not change significantly. Before HD, Con-A--activated suppressor cells exerted a stimulatory action on autologous responder cells measured in two-step culture. During HD, Con-A-activated suppressor cell activity transiently appeared, with its peak at 60 min after the start of HD. It was accompanied by a transient rise in lymphocyte count with spontaneous interleukin-2 (IL-2) receptor expression, whereas the number of cells expressing IL-2 receptor following phytohemaglutinin (PHA) stimulation was progressively decreased during HD. A significant correlation was found between the increment of Con-A-activated suppressor cell activity and the increment of spontaneous IL-2 receptor expression on lymphocytes during one single blood flow through the dialyzer. The results supply further evidence that HD may impose additional disturbances on immune regulation in chronic uremics.

Collagen arthritis in the rat is initiated by CD4+ T cells and can be amplified by iron

The role of iron in arthritis was studied by administering ferric citrate (Fe-cit) to age-matched, female Sprague-Dawley rats immunized with chick type II collagen on Day 0. Rats received intravenously (iv) either Fe-cit (7.7 mg/kg body wt) or an identical concentration of sodium citrate on varying days after immunization. Transferrin saturation peaked (88-95%) 1 hr post-Fe-cit and returned to baseline values within 24 hr. Injection of Fe-cit on either Day 3 or Day 5, but not on Day 7 or Day 9, significantly (P less than 0.03) increased the incidence of arthritis. Synovium from the infrapatellar fat pad was harvested on Days 0-10 for analysis by immunocytochemistry. The inceptual morphologic change in the synovium following collagen immunization in rats not injected iv was an increase in the number of CD4+ and transferrin receptor+ mononuclear cells in perivascular regions; compared to Day 0 both cell types had increased two- to threefold by Day 3. On Day 7, an increase in CD8+ mononuclear cells occurred and the first polymorphonuclear leukocytes were noted. These alterations resulted in a peak in the CD4-CD8 ratio on Day 3, with a gradual decline thereafter. Although Fe-cit administration promoted the ingress of these mononuclear cells, it did not change the CD4-CD8 ratio significantly or recruit polymorphonuclear leukocytes into the joint tissue. Serum antibody titers to type II collagen, measured 20 days after immunization by an enzyme-linked immunosorbent assay, and delayed-type hypersensitivity to collagen, measured by a radiometric ear assay on Day 23, did not differ significantly between the groups. As well as showing that the initial intrasynovial event in collagen arthritis is perivascular infiltration by members of the CD4+ T cell subset displaying a phenotypic sign of activation, these findings demonstrate that iron administered at a critical time after immunization enhances the induction of collagen arthritis. The coincidence of this brief period of susceptibility with maximum CD4-CD8 ratios within the synovium and its occurrence prior to the stage of neutrophil infiltration are consistent with the possibility that the augmenting effect of iron is mediated by the inducer T cell subset.

The mechanism of pH-dependent hydrogen peroxide cytotoxicity in vitro

The present paper is concerned with the influence of hydrogen ion concentration and composition of the medium on clonogenic survival of epithelial cells exposed to hydrogen peroxide in vitro. The survival of cells incubated with H2O2 in phosphate-buffered saline at pH 6.5 was 1 x 10(-2) and increased abruptly to 9 x 10(-2) at pH 7.0. The pH dependence of the cytocidal effect was particularly conspicuous when Eagle's minimum essential medium (SFMEM) was used for cell exposure to H2O2: the survival was characterized by exponential pH dependence and varied from 1 x 10(-1) to 9 x 10(-1) for pH 6.5 and 7.5, respectively, with a superimposed sharp peak value of 9 x 10(-1) at pH 7.0. The enhanced pH dependence of the H2O2 cytotoxicity in SFMEM was found to result from the additive action of glucose and histidine present in this medium. Glucose alone protected the cells with the efficiency decreasing with increasing hydrogen ion concentration. Histidine was responsible for the intermediate maximum in the pH-dependent survival spectrum. In addition, the changes in cell survival were accompanied by pH-dependent release of GSSG from the exposed cells. The GSSG efflux was inhibited by glucose in the medium. The influence of glucose on both the pattern of cell survival and the associated GSSG release indicate that the glutathione peroxidase activity supported by the pentose phosphate pathway is crucial in cell protection against extracellular H2O2 toxicity.

Structural damage to lymphocyte nuclei by H2O2 or gamma irradiation is dependent on the mechanism of OH. radical production

Normal human lymphocytes were exposed to OH. radicals produced indirectly by exposure to H2O2 or directly by gamma irradiation. Using a flow cytometry technique to measure changes in nucleoid size, it was found that generation of OH. in each system produced a characteristic relaxation in nuclear supercoiling. Exposure of cells to H2O2 produced a metal-dependent step-wise relaxation in extracted nucleoids, while gamma irradiation induced a gradual dose-dependent increase in nucleoid size. The site-specific metal-dependent changes produced in lymphocytes incubated in H2O2 should also occur in gamma irradiated cells, but the characteristic effects on nuclear supercoiling would not be detected within the background of random DNA damage. The importance of metals in maintaining the supercoiled loop configuration of DNA within the protein matrix suggests that free radical damage at metal locations may be particularly toxic for the cell.

The T cell system in rheumatoid arthritis: activated or defective?

Rheumatoid Arthritis (RA) is characterised by the presence of activated lymphocytes in the synovial compartment, which are classically considered to be of particular importance to the pathogenesis of the disease. We have shown that activated lymphocytes are also found in the rheumatoid lymph nodes and peripheral blood, and that their proportions are increased in early or active disease. Double-labelling experiments showed that T cell subsets within the activated circulating lymphocytes resemble closely those found in the synovium, and suggested an important role for circulating activated lymphoid populations in the pathogenesis of RA. In vitro studies indicate that although rheumatoid lymphocytes express activation markers, they are functionally deficient. This is well established in the case of synovial lymphocytes. We have demonstrated that functional defects are also present in circulating rheumatoid lymphocytes, which show a decreased autologous mixed leucocyte response (AMLR), corrected partially by the addition of exogenous IL-2. They also proliferate poorly in response to PHA and produce significantly less IL-2 than normal controls. This is more marked in patients with active or complicated RA. These defects cannot be explained by a lack of CD4+2H4+ cells which we have shown to be the major IL-2-producing circulating lymphocyte subpopulation. These findings suggest an intrinsic-functional rather than a numerical deficiency of the IL-2 producing T cells in RA. In recent experiments we have shown that non-lymphoid populations, such as activated phagocytic cells, are also involved in the deficient rheumatoid T cell function, partly via the production of prostaglandins and reactive oxygen intermediates. We and others have demonstrated that the latter may significantly and selectively affect lymphocyte viability and function. These findings may explain the differences in the functional capacity of lymphocytes frequently observed between cells derived from different sites or at different stages of the disease. We suggest that it is not lymphocyte activation as such, but its defective nature, that is of pathogenetical importance in RA. Furthermore, the T cell system should not be viewed and studied in isolation in this disease, but its interactions with inflammatory cells should be taken into account.