Characterisation of myeloid cells in circulation and synovial fluid of patients with psoriatic arthritis

Objective Psoriatic arthritis (PsA) is an inflammatory arthritis associated with psoriasis. Adding to studies focused on the role of T cells and macrophages, we sought to investigate the systemic activation of leukocytes in PsA.Methods We assessed the activation state of leukocyte populations, including polymorphonuclear neutrophils (PMNs) and monocyte/macrophages, in blood and synovial fluid (SF) by multicolour flow cytometry. We also evaluated the correlation between leukocyte numbers and expression of activation markers with disease activity parameters.Results SF PMNs showed an elevated activation state compared with blood PMNs, but a reduced activation state compared with oral PMNs of non-arthritic controls. In vitro stimulation caused SF PMNs to become further activated, demonstrating that they retain a reserve capacity for activation in response to specific triggers. We found significant variability between patients in the expression of SF PMN CD activation markers, indicating a range of possible activation states across patients. However, PMN CD marker expression remained consistent over two sequential visits in a subset of patients, indicating patient-specific distinct inflammatory states during flares. We further found that markers of disease activity increased with elevated SF macrophage numbers. Expression of several CD markers on blood or SF cells, for example, PMN expression of the high-affinity Fc-receptor CD64, correlated with disease activity markers, including pain score and Disease Activity in Psoriatic Arthritis score.Conclusion These preliminary findings support a potential role for surface antigens on PMNs and monocytes/macrophages as prognostic or disease activity monitoring tools.