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.