Anti-Citrullinated Protein Antibodies Induce Macrophage Subset Disequilibrium in RA Patients

Abstract

We used samples from rheumatoid arthritis (RA) patients to examine whether Anti-citrullinated protein antibodies (ACPAs) alter macrophage subset distribution and promote RA development. Macrophage subset distributions and interferon regulatory factor 4 (IRF4) and IRF5 expressions were analyzed. ACPAs were purified by affinity column. After RA and osteoarthritis (OA) patients' macrophages were cocultured with ACPAs, macrophage subsets and IRF4 and IRF5 expressions were measured. Small interfering RNAs (siRNAs) were transfected into ACPA-activated cells to suppress IRF4 or IRF5. Fluorescence-activated cell sorting (FACS), Western blot, and immunohistochemistry were performed. Macrophage subset disequilibrium occurred in RA patient synovial fluids. IRF4 and IRF5 were all expressed in the synovial fluid and synovium. ACPAs (40 IU/ml) could induce macrophages to polarize to M1 subsets, and the percentage of increased M1/M2 ratio of RA patients was higher than that of the OA patients. ACPAs also induce IRF4 and IRF5 protein expressions. IRF5 siRNA transfection impaired ACPA activity significantly. We demonstrated that macrophage subset disequilibrium occurred in RA patients. ACPAs induced IRF5 activity and led to M1 macrophage polarization.

Rheumatoid arthritis CD14+ monocytes display metabolic and inflammatory dysfunction, a phenotype that precedes clinical manifestation of disease

“…In RA, myeloid cell effector functions may be influenced by citrullinated proteins. ACPA positivity has been shown to influence the inflammatory status of monocyte‐derived macrophages, with ACPA from RA synovial fluid initiating a shift in peripheral blood monocytes towards a pro‐inflammatory macrophage phenotype in vitro 41 . Another study reported that ACPA promote IL‐1β release from macrophages via AKT/NFκB and subsequent activation of the NLRP3 inflammasome 42 .…”

Autoantibody Biomarkers in Rheumatic Diseases

“…In addition to IC formation with citrullinated proteins and induction of cytokine secretion, FcR engagement by ACPAs are also able to polarize macrophages to the pro-inflammatory M1 subset through interferon regulatory factors 4 and 5 pathways, leading to a higher M1/M2 ratio in RA patients than in osteoarthritis patients [22].…”

The Central Role of Acute Phase Proteins in Rheumatoid Arthritis: Involvement in Disease Autoimmunity, Inflammatory Responses, and the Heightened Risk of Cardiovascular Disease

“…108,183 The presence of ACPAs causes a dysregulated M1/M2 macrophage subset polarization, favoring M1 (classical) activation. 184 The M1 subset is characterized by its inflammatory, microbicidal, and tumoricidal properties. 184 There is an overexpression of TLR2 and TLR4 receptors by macrophages and synovial fibroblasts in RA.…”

“…184 The M1 subset is characterized by its inflammatory, microbicidal, and tumoricidal properties. 184 There is an overexpression of TLR2 and TLR4 receptors by macrophages and synovial fibroblasts in RA. 117 TLRs recognize disease-associated molecular patterns (DAMPs) and PAMPs, resulting in innate immune responses.…”