Dendritic cells are a heterogeneous group of antigen presenting cells that link the innate and adaptive immune system. Due to their unique role in controlling naïve T cell responses, DC and subsequent T cell responses are hypothesised to be involved in the pathogenesis of RA and PsA. Indeed, the strongest evidence to suggest that DC may play a role in these diseases is the genetic association between mutations in the HLA alleles and disease development and severity, further supporting the role of antigen specific T cells. Autoreactive T cells against citrullinated self-proteins have also been identified within the joint and previous studies examining DC in IA in synovial tissue, note that these cells are contained in lymphoid aggregates, in close proximity to T cells. It is now appreciated the DC and T cells can be subdivided into distinct subsets, each with unique functions, however the overall contribution of these specific DC and T cell subsets to the pathogenesis of RA and PsA is relatively unknown – especially at the translational level. Therefore our group uses primary human tissues and samples to phenotype and functionally assess the contribution of specific DC and T cell subsets to disease. Furthermore, we also aim to explore the functional consequences of the joint microenvironment on these cells and how it may ultimately affect their overall phenotype and function.