TCR-triggered extracellular superoxide production is not required for T-cell activation

Abstract

BackgroundIn the last decade, reactive oxygen species (ROS) production has been shown to occur upon T-cell receptor (TCR) stimulation and to affect TCR-mediated signalling. However, the exact reactive species that are produced, how ROS are generated and their requirement for T-cell activation, proliferation or cytokine production remain unclear, especially in the case of primary human T cells. Moreover, several groups have questioned that ROS are produced upon TCR stimulation.ResultsTo shed some light onto this issue, we specifically measured superoxide production upon TCR ligation in primary human and mouse T lymphocytes. We showed that superoxide is indeed produced and released into the extracellular space. Antioxidants, such as superoxide dismutase and ascorbate, abolished superoxide production, but surprisingly did not affect activation, proliferation and cytokine secretion in TCR-stimulated primary human T cells. It has been suggested that T cells produce ROS via the NADPH oxidase 2 (NOX2). Therefore, we investigated whether T-cell activation is affected in NOX2-deficient mice (gp91phox −/−). We found that T cells from these mice completely lack inducible superoxide production but display normal upregulation of activation markers and proliferation.ConclusionsCollectively, our data indicate that primary T cells produce extracellular superoxide upon TCR triggering, potentially via NOX2 at the plasma membrane. However, superoxide is not required for T-cell activation, proliferation and cytokine production.

T cells and reactive oxygen species

“…The intriguing possibility is that reduction in the synthesis of leukotrienes (proinflammatory molecules downstream of lipoxygenase), rather than reduction in ROS levels per se [ 76 ], could be the reason for the impairment of T-cell activation by lipid-soluble antioxidants. This hypothesis is in agreement with the findings that NOX-2 deficient T cells have normal CD25 and CD69 expression, IL-2 production, and proliferation [ 65 , 69 ].…”

“…Interestingly, gp91 phox−/− T cells have no defect in CD25 expression or IL-2 production [ 69 ]. This was confirmed by a recent study, which showed that T cells from gp91 phox−/− mice have the normal expression of CD25 and CD69 and normal proliferation [ 65 ]. Thus, NOX-2 is required for proper differentiation but not for the activation of primary murine T cells.…”

“…TCRxCD28 stimulation of human or murine T cells induces extracellular O 2 •- production, measured using the luminol-based Diogenes system. O 2 •- production is completely abrogated in T-cell preparations from NOX-2-deficient mice [ 65 ]. Similarly, TCR stimulation of murine CD4 + T cells induces NOX-2-dependent DCFDA oxidation [ 66 ].…”

“…In human T cells, nordihydroguaiaretic acid (NDGA) inhibits IL-2 synthesis [ 74 ], whereas vitamin E suppresses IL-4 production [ 75 ]. Interestingly, catalase, superoxide dismutase, and ascorbate do not affect the expression of CD25 and CD69, proliferation, and cytokine production in human T cells [ 65 ]. It seems that antioxidants that inhibit lipid peroxidation and/or lipoxygenase activity (such as NDGA, BHA, Vitamin E, or Mitovitamin E), but not antioxidants that scavenge water-soluble ROS (such as catalase, superoxide dismutase, or ascorbate) can interfere with the activation of primary T cells (Fig.…”

Exophilin-5 regulates allergic airway inflammation by controlling IL-33–mediated Th2 responses

“…In the present study, we showed that deficiency of the Rab27 effector, exophilin-5, exacerbated allergic lung inflammation and that expressed in CD4 + T cells (38) and is responsible for extracellular superoxide release by CD4 + T cells upon TCR stimulation (39). In fact, the levels of Nox2-encoding Cybb mRNA in pathogenic Th2 cells were much higher than those in total CD4 + Th cells ( Figure 9A) or 3 other fractions of splenic memory-type Th cells, and were not affected by exophilin-5 deficiency ( Figure 9B).…”