Anti-mutated citrullinated vimentin antibodies in rheumatoid arthritis patients: Relation to disease activity and manifestations

An Overview of the Intrinsic Role of Citrullination in Autoimmune Disorders

A protein undergoes many types of posttranslation modification. Citrullination is one of these modifications, where an arginine amino acid is converted to a citrulline amino acid. This process depends on catalytic enzymes such as peptidylarginine deiminase enzymes (PADs). This modification leads to a charge shift, which affects the protein structure, protein-protein interactions, and hydrogen bond formation, and it may cause protein denaturation. The irreversible citrullination reaction is not limited to a specific protein, cell, or tissue. It can target a wide range of proteins in the cell membrane, cytoplasm, nucleus, and mitochondria. Citrullination is a normal reaction during cell death. Apoptosis is normally accompanied with a clearance process via scavenger cells. A defect in the clearance system either in terms of efficiency or capacity may occur due to massive cell death, which may result in the accumulation and leakage of PAD enzymes and the citrullinated peptide from the necrotized cell which could be recognized by the immune system, where the immunological tolerance will be avoided and the autoimmune disorders will be subsequently triggered. The induction of autoimmune responses, autoantibody production, and cytokines involved in the major autoimmune diseases will be discussed.

Cytokines (IL-15, IL-21, and IFN-γ) in rheumatoid arthritis: association with positivity to autoantibodies (RF, anti-CCP, anti-MCV, and anti-PADI4) and clinical activity

INTRODUCTION

Rheumatoid arthritis (RA) is an autoimmune disease characterized by synovial membrane damage and autoantibody production. RA is a heterogeneous disease, where cytokines such as IL-15, IL-21, and IFN-γ have been associated. However, their association with the autoantibodies has not been clearly described. The aim of this study was to evaluate the relationship between the cytokines IL-15, IL-21, and IFN-γ with the autoantibodies (RF, anti-CCP, anti-MCV, and anti-PADI4) in RA and disease activity.

METHODOLOGY

This study included 153 RA patients and 80 control subjects (CS). The levels of IL-15, IL-21, IFN-γ, anti-CCP, anti-MCV, and anti-PADI4 were quantified by ELISA, whereas RF was quantified by turbidimetry. The disease activity was evaluated by the indices disease activity score 28-erythrocyte sedimentation rate (DAS28-ESR), clinical disease activity index (CDAI), and simple disease activity index (SDAI).

RESULTS

The serum levels of IL-15, IL-21, and IFN-γ, and autoantibodies were increased in RA patients, compared with CS (p < 0.05). A correlation was found between IL-21 and anti-CCP and anti-MCV (p < 0.05). According to RA evolution, RF, anti-CCP, and anti-MCV had higher levels in early RA. In addition, increased levels of IL-21 were observed in RA seropositive patients (RF/anti-CCP/anti-MCV). The higher levels of both cytokines and autoantibodies were observed in moderate activity, evaluated by the three indices.

CONCLUSIONS

Our results suggest that the increased soluble levels of IL-15, IL-21, and IFN-γ are involved in the inflammatory network in RA. However, IL-21 serum levels are associated with higher titers of autoantibodies (RF, anti-CCP, and anti-MCV) and IL-15 with moderate activity. Key Points • IL-15, IL-21, and IFN-y are associated with the immunopathology of RA, but not significantly with the evolution of the disease. • RF, anti-CCP, and anti-MCV had higher levels in early than established RA. • IL-21 has an association with RF, anti-CCP, and anti-MCVand, for this reason, could be proposed as a disease biomarker. • Patients with activity moderate of disease showed higher levels of RF, anti-CCP, anti-MCV, and IL-15.