Monocyte/Macrophage Subsets in the Peripheral Blood, Their Related Cytokines, and Circulating Markers of Fibrosis in Active Takayasu Arteritis and Longitudinal Changes Following Immunosuppressive Therapy

Purpose: Takayasu arteritis (TAK) is a rare, stenosing large vessel vasculitis characterised by arterial wall fibrosis. Longitudinal changes in circulating monocyte/macrophage populations, which drive both inflammation and fibrosis in TAK, have not been studied. Patients and Methods: Circulating monocyte/macrophage populations, related cytokines, and markers of fibrosis were evaluated longitudinally in active TAK and compared with healthy controls. Flow cytometry was performed on peripheral blood mononuclear cells to identify overall CD14+CD66b-, M1-like, and M2-like monocytes/macrophages. Serum M1-like (TNF-α, IL-1β, IL-6, IP-10, IL-12p40, IL-23) and M2-like cytokines (IL-1RA, IL-10, CCL17) and circulating proteins indicating arterial wall fibrosis [plasma hyaluronic acid (HA), procollagen-III aminoterminal propeptide (PIIINP), tissue inhibitor of metalloproteinase 1 (TIMP-1), serum transforming growth factor-beta (TGF-β)] were estimated using cytokine bead array or ELISA. Mann–Whitney U -test was used for unpaired analysis, and Wilcoxon matched-pairs signed-rank test for paired analysis; p< 0.05 was considered statistically significant (after correction for multiple testing). Results: Eighteen patients with active TAK and 8 age- and sex-similar healthy controls were recruited. Patients with active TAK had higher circulating overall, M1-like, and M2-like monocytes/macrophages than controls (p< 0.001). M1-like cytokines TNF-⍺, IL-6, and IL-23, and M2-like cytokine IL-1RA were higher in active TAK than controls (p< 0.001). Circulating markers of fibrosis HA and PIIINP were significantly elevated in active TAK than controls (p< 0.05). Following immunosuppressive therapy, a significant decrease in overall and M1-like monocytes/macrophages and related cytokines (TNF-⍺, IL-1β, IL-6, IL-12p40, IP-10, IL-23) concomitant with an increase in M2-like monocytes/macrophages, related M2-like cytokines (IL-10, CCL17) and circulating markers of fibrosis (HA, TIMP-1, PIIINP, TGF-β) was observed (p< 0.05). Conclusion: A transition from M1-like to M2-like monocyte/macrophage populations with an increase in circulating markers of fibrosis is seen in the peripheral blood following immunosuppressive therapy in active TAK. Future treatment strategies should evaluate a combination of anti-fibrotic agents with immunosuppressive therapy in TAK. The diagram illustrates the process of blood collection and analysis for patients with active TAK, inactive TAK after treatment and healthy controls. Blood is drawn using plain and EDTA tubes. Peripheral blood mononuclear cells, serum and plasma are collected. Flow cytometry and cytokine bead array are used for analysis, along with ELISA. M1-like monocytes/macrophages produce cytokines such as TNF-alpha, IL-1beta, IL-6, IL12p40, IL-23 and IP-10. M2-like monocytes/macrophages produce IL-1RA, IL-10 and CCL-17. Circulating proteins associated with fibrosis include HA, TIMP-1, PIIINP and TGF-beta. Comparisons are made between active TAK and healthy controls, showing increased monocytes/macrophages, M1-like and M2-like cytokines and fibrosis markers in active TAK. After immunosuppressive therapy, inactive TAK show decreased overall monocytes/macrophages and M1-like monocytes/macrophages and their related cytokines, increased M2-like monocytes/macrophages and their related cytokines and circulating fibrosis markers.Diagram of blood analysis and cytokine profiles in active/inactive TAK patients and healthy controls.