The number of circulating monocytes as biomarkers of the clinical response to methotrexate in untreated patients with rheumatoid arthritis.

Background: The aim of this work was to analyze the number and distribution of circulating monocytes, and of their CD14(+high)CD16(-), CD14(+high)CD16(+) and CD14(+low)CD16(+) subset cells, in treatment-naive patients with rheumatoid arthritis (RA), and to determine their value in predicting the clinical response to methotrexate (MTX) treatment.

Methods: This prospective work investigated the number of circulating monocytes, and the numbers of CD14(+high)CD16(-), CD14(+high)CD16(+) and CD14(+low)CD16(+) subset cells, in 52 untreated patients with RA before MTX treatment, and at 3 and 6 months into treatment, using flow cytometry.

Results: The absolute number of circulating monocytes, and the numbers of CD14(+high)CD16(-), CD14(+high)CD16(+) and CD14(+low)CD16(+) subset cells, were significantly higher in MTX non-responders than in responders and healthy controls before starting and throughout treatment. Responders showed normal numbers of monocytes, and of their subset cells, over the study period. The pre-treatment absolute number of circulating monocytes, and the numbers of CD14(+high)CD16(-) and CD14(+high)CD16(+) subset cells, were found to be predictive of the clinical response to MTX, with a sensitivity and specificity of >70% and >88%, respectively.

Conclusions: Treatment-naive patients with RA showed an anomalous distribution of circulating monocyte subsets, and an anomalous number of cells in each subset. A higher pre-treatment number of circulating monocytes, and higher numbers of CD14(+high)CD16(-) and CD14(+high)CD16(+) subset cells, predict a reduced clinical response to MTX in untreated patients with RA.