Interleukin-34 can predict joint damage progression in patients with rheumatoid arthritis

This study investigated whether the levels of interleukin-34 can predict joint damage in patients with rheumatoid arthritis (RA).

Joint damage is observed in about 50% of rheumatoid arthritis patients after less than 10 months of disease. The rate of damage progression tends to be highest in the first two years of illness, but can be faster and more severe for some patients. Identifying a biomarker (measurable indicators of a biologic state or condition; usually proteins) that can predict more aggressive and damaging rheumatoid arthritis would be beneficial.

Interleukin-34 is a recently discovered protein involved in inflammation. Increased levels of interleukin-34 have been observed in the joint tissue, blood, and synovial fluid (fluid found in joints) of patients with rheumatoid arthritis. However, whether interleukin-34 contributes to radiographic progression (objective measure of the visible joint damage using x-rays) in patients remains unclear.

This study included 195 individuals: 100 rheumatoid arthritis patients, 36 patients with ankylosing spondylitis (another form of arthritis), and 59 healthy individuals for comparison. Blood interleukin-34 levels were measured in all patients. Interleukin-34 was also measured in synovial fluid from 18 rheumatoid arthritis patients and 19 patients with osteoarthritis. Progression of structural damage was assessed in 81 patients with rheumatoid arthritis by plain radiographs (x-ray) at the beginning of the study and after an average 1.6 years.

Significantly higher levels of interleukin-34 were found in the blood samples of patients with rheumatoid arthritis (603.5 pg/ml) or ankylosing spondylitis (417 pg/ml) compared to healthy individuals (152 pg/ml). Significantly higher interleukin-34 levels were also found in the synovial fluid of patients with rheumatoid arthritis (5069 pg/ml) compared to patients with osteoarthritis (235 pg/ml).

Blood interleukin-34 levels were predictive of later radiographic progression. Patients with the lowest levels of interleukin-34 had the lowest rate of progression (3.6%), patients with medium levels had 30.0% rate of radiographic progression, and patients with the highest levels had the highest rate of radiographic progression (52.2%).

The authors concluded that interleukin-34 may play a role in rheumatoid arthritis-associated joint damage and is a potential biomarker for predicting subsequent radiographic progression.