FRI0051 In Vivo Imaging To Characterise The Specificity, Function and Behavior of The CD4+ T Cells Initiating Articular Inflammation
Authors: R.A. Benson, C.T. Prendergast, I.B. McInnes, J.M. Brewer, P. Garside
Journal: Annals of the Rheumatic Diseases (2016)

<h3>Background</h3> It is widely accepted that CD4<sup>+</sup> T cells are important contributors to the pathogenesis of Rheumatoid Arthritis (RA). The presence of activated T cells in the inflamed synovium, GWAS defined associations with HLA-DR4, ptpn22, ctla4 and cd28, together with the clinical success of CTLA-4-Ig, all implicate a significant contribution (1). Yet it remains unclear when and where CD4<sup>+</sup> T cells mediate this pathogenic effect and whether the specificity of the cells is important. <h3>Objectives</h3> Characterise the specificity and function of the CD4<sup>+</sup> T cells mediating the initiation of experimental arthritis. To relate this to an analysis of the migratory behaviour of CD4<sup>+</sup> T cells in the inflamed articular environment thereby defining interactions with antigen presenting cells (APCs) that may control their activation in the joint. <h3>Methods</h3> Antigen-induced arthritis using ovalbumin (OVA) as the inciting challenge was used to model articular inflammation (2). Th1 OVA specific fluorescent (DsRed) OT-II TcR transgenic T cells were adoptively transferred and expanded <i>in vivo</i> by challenge with OVA/CFA. This allowed analysis and in tracking of antigen-specific T cells as they were recruited to the joint following periarticular injection of heat aggregated OVA (HAO). Flow cytometry allowed phentoyping of cells recruited to the inflamed articular environment. The T cell receptor (TcR) diversity of infiltrating endogenous T cells was assessed by PCR of Vβ genes. Dynamic interactions of responding DSRed T cells with joint residing YFP dendritic cells (DCs) were visualized using intravital multiphoton microscopy. <h3>Results</h3> Low numbers of the inciting OVA specific CD4<sup>+</sup> T cells could be found in the joint tissue. However, a large influx of endogenous CD4<sup>+</sup> T cells of unknown antigen specificity was also detected. This recruited articular T cell population expressed surface activation markers, exhibited a narrower range of T cell receptor Vβ usage and upon <i>ex vivo</i> restimulation produced TNFα and IFNγ. Intravital imaging of the inflamed joint revealed that a sub-population of this infiltrate demonstrated slower motility speeds and longer periods of contact with articular DCs, while others rapidly migrated throughout the tissue. <h3>Conclusions</h3> We define for the first time the <i>in vivo</i> kinetics of early T cell induction of articular inflammation. Numbers of the inciting antigen-specific population recruited to the joint tissue is small, but is associated with a subsequent influx of a large endogenous population of CD4<sup>+</sup> T cells of unknown antigen specificity that acquired the ability to secrete pro-inflammatory cytokines. The narrower usage of TcR Vβ genes by the CD4<sup>+</sup> T cells in the inflamed joint suggests some degree of antigen-specificity in recruitment while intravital imaging reveals that some of this infiltrate exhibits behaviour consistent with recognition of cognate peptide-MHCII. <h3>References</h3> Benson RA et al. Mechanisms of autoimmunity in human disease: a critcal review of current dogma. Curr Opin Rheumatol. 2014; 26(2): 197 Maffia P et al. Inducing experimental arthritis and breaking self-tolerance to joint-specific antigens with trackable, ovalbumin-specific T cells. J Immunol. 2004;173(1):151 <h3>Acknowledgement</h3> This research is funded by Arthritis Research UK, and supported by Arthritis Research UK Rheumatoid Arthritis Pathogenesis Centre of Excellence – RACE <h3>Disclosure of Interest</h3> None declared