Hydrogen peroxide-mediated inhibition of T-cell response to mitogens is a result of direct action on T cells

Immunosuppressive Effects of Myeloid-Derived Suppressor Cells in Cancer and Immunotherapy

The primary function of myeloid cells is to protect the host from infections. However, during cancer progression or states of chronic inflammation, these cells develop into myeloid-derived suppressor cells (MDSCs) that play a prominent role in suppressing anti-tumor immunity. Overcoming the suppressive effects of MDSCs is a major hurdle in cancer immunotherapy. Therefore, understanding the mechanisms by which MDSCs promote tumor growth is essential for improving current immunotherapies and developing new ones. This review explores mechanisms by which MDSCs suppress T-cell immunity and how this impacts the efficacy of commonly used immunotherapies.

Quantifying mitochondrial respiration in human lymphocytes and monocytes challenged with hydrogen peroxide

Improved technology for the bioenergetic profiling of human blood cells enables population-based screening for alterations in mitochondrial respiration. Mitochondria are sensitive to oxidative stress, and the aim of this study was to quantify mitochondrial respiration in freshly isolated lymphocytes and monocytes challenged with a bolus of H₂O₂. Mitochondrial reserve capacity, calculated as the difference between basal oxygen consumption and maximal activity after uncoupling of the electron transport chain, was the most sensitive to H₂O₂. Treatment of lymphocytes with 20 μM H₂O₂ reduced the reserve capacity by approximately 50%, while monocyte reserve capacity was five times more resistant. Healthy donors of a similar age were tested to determine the variation between individuals, and within the same individuals tested on several different occasions. Lymphocytes obtained from a population of people aged 70-80 years showed a similar inhibition upon challenge with H₂O₂ as those aged 18-25 years, indicating no decline in resilience with age.

Comparative effect of fucoxanthin and vitamin C on oxidative and functional parameters of human lymphocytes

The aim of this study was to evaluate the effects of FUCO alone or combined with vitamin C on different features of lymphocyte function related to ROS/RNS (reactive oxygen/nitrogen species) production. For this purpose we have evaluated the cytotoxicity of increasing concentrations of FUCO and vitamin C, the proliferative capacity of stimulated T- and B-lymphocytes, superoxide anion radicals (O(2)), hydrogen peroxide (H(2)O(2)) and nitric oxide (NO) production, antioxidant enzyme activities and the indexes of oxidative damage in proteins (carbonyl and thiol content). We have also evaluated the release of inflammatory cytokines and glucose-6-phosphate dehydrogenase (G6PDH) activity. Healthy human lymphocytes were acutely treated in vitro with FUCO (2 μM) with or without vitamin C (100 μM). Results revealed that human lymphocytes treated with FUCO at 2μM did not present any significant alteration in the proliferation of T- and B-lymphocytes at both resting and stimulated conditions. Moreover, FUCO used at low concentrations showed more pro-oxidant than antioxidant effects, which were recognized by the increased H(2)O(2) and increased NO production. Anti-inflammatory activity of FUCO was confirmed by significantly increased IL-10 and decreased TNF-α production. Vitamin C increased T-lymphocyte proliferation, whereas vitamin C plus FUCO promoted a reduction in the proliferation rate of these cells. All groups decreased pro-inflammatory cytokine TNF-α and increased anti-inflammatory IL-10 production although only vitamin C decreased IFN-γ either alone or when combined with FUCO. Overall, the combination of the antioxidants had more antioxidant and anti-inflammatory effects than when they were applied alone.

Neutrophil uptake of nitrogen-bisphosphonates leads to the suppression of human peripheral blood γδ T cells

Nitrogen-bisphosphonates (n-BP), such as zoledronate, are the main class of drugs used for the prevention of osteoporotic fractures and the management of cancer-associated bone disease. However, long-term or high-dose use has been associated with certain adverse drug effects, such as osteonecrosis of the jaw and the loss of peripheral of blood Vγ9Vδ2 T cells, which appear to be linked to drug-induced immune dysfunction. In this report we show that neutrophils present in human peripheral blood readily take up zoledronate, and this phenomenon is associated with the potent immune suppression of human peripheral blood Vγ9Vδ2 T cells. Furthermore, we found this zoledronate-mediated inhibition by neutrophils could be overcome to fully reconstitute Vγ9Vδ2 T cell proliferation by concomitantly targeting neutrophil-derived hydrogen peroxide, serine proteases, and arginase I activity. These findings will enable the development of targeted strategies to mitigate some of the adverse effects of n-BP treatment on immune homeostasis and to improve the success of immunotherapy trials based on harnessing the anticancer potential of peripheral blood γδ T cells in the context of n-BP treatment.

Cross-linking of MHC class II molecules interferes with phorbol 12,13-dibutyrate-induced differentiation of resting B cells by inhibiting Rac-associated ROS-dependent ERK/p38 MAP kinase pathways leading to NF-kappaB activation

In addition to their essential role in antigen presentation, major histocompatibility complex (MHC) class II molecules have been described as the receptor associated with signal transduction regulating B-cell function. In previous experiments, we found that cross-linking of MHC class II molecules with corresponding anti-MHC class II antibodies inhibited NF-kappaB-activated signaling pathways associated with the proliferation and differentiation of the LPS-stimulated primary and resting B-cell line, 38B9. We also found that exposure to the anti-MHC class II antibody reduced the production of ROS, which function as secondary signal transducers, in the phorbol 12,13-dibutyrate (PDBU)-treated (but not in the LPS-treated) resting B-cell line. In this study, we investigated the molecular mechanisms in the ROS-associated signaling pathway leading to PDBU-induced NF-kappaB activation that results in B-cell differentiation and speculated that the signaling pathway was inhibited by exposure to the anti-MHC class II antibody. We also found that this inhibition was mediated through down-regulation of the activated Rac/ROS-associated ERK/p38 MAPK signaling pathway in PDBU-treated 38B9 cells. Collectively, these findings suggest that ROS-associated molecules are involved in MHC class II-associated negative signal transduction in resting B cells.

T cell receptor stimulation, reactive oxygen species, and cell signaling

In the immune system, much of the focus on reactive oxygen species (ROS) has been regarding their role in antimicrobial defense as part of the innate immune system. In addition to this role, it is now becoming clear that ROS are used by cells of the adaptive immune system as regulators of signal transduction by cell surface receptors. The activation of T lymphocytes through their specific antigen receptor [T cell receptor (TCR)] is vital in regulating the immune response. Much experimental evidence has suggested that activation of T cells is redox dependent and recent studies have shown that engagement of the TCR induces rapid production of ROS. This review examines the evidence for TCR-stimulated generation of ROS and discusses the role(s) of receptor-stimulated ROS production in T cell signal transduction and gene expression.

A study of tissue interface membranes from revision accord knee arthroplasty: the role of T lymphocytes

Despite four decades of advances in the design of orthopaedic devices aseptic loosening remains a major cause for the revision of total joint arthroplasty. This study used the techniques of immunohistochemistry and reverse transcription polymerase chain reaction to identify the inflammatory cell types, cytokines and chemokines within the interface tissue surrounding failed Accord Knee prostheses. Many T cells were identified within the tissue: however, the classical marker of activation, CD25 was expressed on very few cells. Molecular analysis failed to detect the synthesis of either Th1 or Th2 cytokines. These results suggest that the T cells are being actively recruited to the site of inflammation along the chemokine gradients but are not participating in a classical immune response.

Protective effect of vitamin E on lymphocyte growth capacity during incubation in vitro

Vitamin E, an essential lipid-soluble micronutrient, plays an important role in the immune system and serves as an immunostimulant in geriatric subjects. Using an in vitro incubation to simulate aging processes, we find that vitamin E mitigates loss of growth capacity in lymphocytes. Vitamin E presence during in vitro incubation did not affect significantly the level of peroxidation, the effects of exogenous IL-2, PGE2, or indomethacin, nor levels of IL-2 production. Thus, the preservative effect on lymphocyte growth by vitamin E is not due primarily to its antioxidant function or to interleukin-2 or prostaglandin effects. The decreased growth capacity generated by in vitro incubation is accompanied by a variety of cellular alterations, including decreased CD5 surface antigen, enhanced suppression by adherent cells, and impaired communication between lymphocytes and adherent cells. The decrease in CD5 surface antigen correlates inversely with the cell density required for maximal cell proliferation, and the diminished CD5 levels were unaltered by vitamin E presence during the aging process. In contrast, protection of T-cell proliferative capacity by vitamin E in vitro correlates with diminished suppression by adherent cells and normalized interaction between lymphocytes and adherent cells.

Human lymphocytes incubated in vitro share multiple characteristics with geriatric-derived lymphocytes: a potential in vitro model for aging?

Aging involves a complicated set of parallel reactions that result in multiple cellular and organismic changes and may eventuate in chronic illness. In the immune system, several alterations that correlate with age have been established. In the present study, we report the results of incubating lymphocytes in vitro in whole blood and, employing measures known to be age-dependent, compare these cells 'aged' in vitro with cells from geriatric patients aged in vivo. Cells from blood aged in vivo and incubated in vitro share a number of common characteristics that include decreased growth capacity, shifted growth patterns, increased suppression by adherent cells, decrease in CD5 surface antigen, similar responses to addition of exogenous IL-1, IL-2, PGE2, or indomethacin, and similar production of PGE2. Differences found between in vivo aging and in vitro incubation are IL-2 plasma levels and IL-2 production by activated cells monitored in conditioned minimal medium. Based on these observations, this in vitro system provides a simple method to generate cells that exhibit a very significant subset, but not all, of the characteristics associated with in vivo aging in lymphocytes.

Superoxide, iron, vascular endothelium and reperfusion injury

It is proposed that vascular endothelium has an intrinsic capacity to generate O2- for regulatory purposes such as inactivation of endothelium-derived relaxing factor. Ischaemia can disrupt the functioning of this oxidant-generating system, resulting in greater O2- generation when O2 is restored. Ischaemia-induced cellular injury can also lead to release of iron ions, that, upon reperfusion, cause conversion of O2- and H2O2 to powerfully-oxidizing species (such as .OH) that further injure the endothelium.