Reactive oxygen species in protein sulphenic acid formation during T cell activation; implications for rheumatoid arthritis

Abstract

In recent years, the effect of reactive oxygen species (ROS) on T cell function in an immune response has gained increasing interest. T cell mediated chronic inflammation is influenced by changes in the redox environment. The cellular surface redox state plays an important role in receptor mediated T cell stimulation. Among many modifications, the reversible nature of sulphenic acid modified proteins act as redox switches to control protein function. T cell membrane proteins contain many cysteine residues that are susceptible to this modification in the presence of ROS. The source of ROS could be paracrine or autocrine by the NADPH complex (NOX) on T cell membrane in response to stimuli. Hence, the presence of free thiols or antioxidants such as thioredoxin (Trx1) and peroxiredoxin (Prx2) on the surface may influence interaction between the T cell receptor (TCR) and antigen presenting cells (APC). The main aims of this study were to analyse the surface redox state during T cell activation and to identify potential membrane proteins that undergo sulphenic acid modification in health and may be relevant to Rheumatoid Arthritis (RA). This thesis has used several approaches to achieve these aims: (1) A cell culture model of T cell-like Jurkat cells was challenged with hydrogen peroxide (H2O2) and novel ROS inducing compounds termed as ROX 1 and ROX 2. (2) Primary CD4+ T cells isolated from healthy individuals were challenged with H2O2 during activation with anti-CD3 and anti-CD28 antibodies. Membrane sulphenic acid modifications were analysed by mass spectrometry approaches. (3) Collagen induced arthritis (CIA) mice model was used to analyse whether ROX plays a role in disease severity. Several sulphenated proteins were identified on the membrane of both Jurkat and primary CD4+ T cells after activation. Activated T cells show increased expression of Trx1 and Prx2 on the surface along with reduced and oxidised thiols in vitro and ex vivo. ROX significantly inhibited T cell activation in human primary CD4+ T cells and WT splenocytes. Compound ROX 2 that targets the NOX2 complex was shown to cause increased release of superoxide anions from WT mouse splenocytes in comparison to Ncf1-/- mice as measured by isoluminol. Results from this study indicated that ROS may not only be responsible for tissue damage but rather a means of modulating the immune response depending on the amount and location produced. This observation was shown confirmed by routine treatment of CIA induced mice with ROX 2. A decreased trend in the severity of arthritis was observed at later onset of the disease in WT mice with ROX 2 and there was no observable difference in Ncf1-/- mice. Therefore, targeting ROS represents a promising therapeutic strategy in dampening antigen-specific T cell responses and T cell-mediated autoimmune diseases. Further studies are required to examine the possible association of Trx1 and Prx2 on the surface proteins during T cell activation and rheumatoid arthritis.