Background It is widely accepted that CD4⁺ 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⁺ T cells mediate this pathogenic effect and whether the specificity of the cells is important.

Objectives Characterise the specificity and function of the CD4⁺ T cells mediating the initiation of experimental arthritis. To relate this to an analysis of the migratory behaviour of CD4⁺ T cells in the inflamed articular environment thereby defining interactions with antigen presenting cells (APCs) that may control their activation in the joint.

Methods 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 in vivo 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.

Results Low numbers of the inciting OVA specific CD4⁺ T cells could be found in the joint tissue. However, a large influx of endogenous CD4⁺ 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 ex vivo 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.

Conclusions We define for the first time the in vivo 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⁺ 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⁺ 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.

1. Benson RA et al. Mechanisms of autoimmunity in human disease: a critcal review of current dogma. Curr Opin Rheumatol. 2014; 26(2): 197

2. 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

Acknowledgement This research is funded by Arthritis Research UK, and supported by Arthritis Research UK Rheumatoid Arthritis Pathogenesis Centre of Excellence – RACE

Disclosure of Interest None declared