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Objective. Increased numbers of IL-17-producing CD4+ T cells have been observed in AS. However, it is not known whether these CD4+ T cells are already present in early disease or if this is a late disease phenomenon only. Therefore we aimed to investigate whether IL-17-producing CD4+ T cells are involved in early active axial SpA, including patients without imaging abnormalities, by determining the frequency and phenotype of IL-17-producing CD4+ T cells in these patients. Methods. Flow cytometry was used to analyse cytokine production and surface marker expression of peripheral blood mononuclear cells from 31 patients suffering from early active HLA-B27-positive axial SpA fulfilling the Assessment of SpondyloArthritis International Society criteria with or without MRI abnormalities and 21 healthy controls. Results. Patients with early active axial SpA showed an increased percentage of IL-17-producing CD4+ T cells compared with healthy controls (mean 1.1% vs 0.4%, respectively; P = 0.013). The percentage of IL-17-producing CD4+ T cells was equally increased in patients with and without MRI abnormalities (1.2% vs 1.1%, respectively; P = 0.81). These IL-17-producing CD4+T cells expressed the αβT cell receptor but not the γδ T cell receptor, exhibited a memory phenotype and expressed CD161, but only sporadically expressed killer cell immunoglobulin-like receptor 3DL2 (KIR3DL2). Conclusion. IL-17-producing CD4+ T cells are increased in patients with early active axial SpA both with and without MRI abnormalities. This finding shows that the frequency of IL-17-producing CD4+ T cells is enhanced in the early stages of disease. [ABSTRACT FROM AUTHOR]

Introduction: Abatacept is a fusion protein of human cytotoxic T-lymphocyte-associated protein (CTLA)-4 and the Fc portion of human immunoglobulin G1 (IgG1). It is believed to be effective in the treatment of rheumatoid arthritis by inhibiting costimulation of T cells via blocking CD28-B7 interactions as CTLA-4 binds to both B7.1 (CD80) and B7.2 (CD86). However, the interaction of CD28 with B7 molecules is crucial for activation of naive cells, whereas it is unclear whether the action of already activated CD4(+) T cells, which are readily present in established disease, also depends on this interaction. The aim of this study was to determine whether the mode of action of abatacept depends solely on its ability to halt T cell activation in established disease., Methods: Arthritis was induced in thymectomized male DBA/1 mice by immunisation with bovine collagen type II. The mice were subsequently depleted for CD4(+) T cells. Abatacept or control treatment was started when 80 % of the mice showed signs of arthritis. Arthritis severity was monitored by clinical scoring of the paws, and anti-collagen antibody levels over time were determined by enzyme-linked immunosorbent assay., Results: Treatment with abatacept in the absence of CD4(+) T cells resulted in lower disease activity. This was associated with decreasing levels of collagen-specific IgG1 and IgG2a antibodies, whereas the antibody levels in control or CD4(+) T cell-depleted mice increased over time., Conclusions: These results show that abatacept decreased disease activity in the absence of CD4(+) T cells, indicating that the mode of action of abatacept in established arthritis does not depend entirely on its effects on CD4(+) T cell activation.