Navigating the diverse immune landscapes of psoriatic arthritis

The goal of remission in psoriatic arthritis (PsA) has remained elusive despite the influx of a range of new therapies over the last 20 years. In contrast, therapeutic responses to agents that inhibit IL-23 or IL-17 have demonstrated impressive efficacy in psoriasis. In part, the divergent responses in these two disorders are likely related to the heterogeneity of tissue involvement in PsA and the interplay of multiple different cell populations and molecular pathways. In this narrative review, we will examine the plasticity of the immune response in PsA from the perspective of the Th17 cell and monocyte and discuss recent findings regarding the importance of CD8+ T resident cells in disease pathogenesis. We will then examine the effects of cytokines on epithelial cell and stromal populations and finally discuss new data regarding immune cell and tissue resident cell cross-talk in entheses and bone. Lastly, the potential therapeutic targets that have emerged from these investigations will be discussed.