Circulating human monocytes, a functionally and phenotypically heterogeneous population, are emerging as fundamental cell types in rheumatoid arthritis (RA). The aim of this pilot study was to assess the correlation, if any, among anti-rheumatic drug therapy, circulating CD14+CD16+ monocytes and validated clinical scales (e.g., DAS28 score and ultrasonography US7 score) of disease severity in RA. Thirty consecutive RA patients, either naïve or under disease-modifying anti-rheumatic drugs (DMARDs) or biological therapy, and 10 age-matched healthy volunteers, were enrolled. Monocytes were prepared from heparinized blood samples; surface expression of CD14 and CD16 was determined by flow cytometry. RA patients presented a significantly higher percentage of CD14+CD16+ monocytes, as compared to healthy subjects. There was a good correlation between DAS28 clinical score and the ultrasound composite score US7 (r = 0.66), as well as between both scores and the percentage of CD14+CD16+ monocytes (r = 0.43 and 0.47, respectively). Naïve RA patients had the highest expression (19.2 ± 3.2%) of CD14+CD16+ monocytes and elevated DAS28 score; patients on DMARDs presented a 7-fold increased expression of CD14+CD16+ monocytes, relatively to healthy volunteers (2.1 ± 1.4%), and an intermediate disease severity. The RA patients treated with biological therapy had a low percentage of CD14+CD16+ monocytes (5.1 ± 3.6%; p < 0.01 vs naïve and DMARDs groups), similar to the one detected in healthy controls, and reduced US7 and DAS28 scores. Interestingly, for the same DAS28 score, monocytes isolated from RA patients on biological therapy had a lower CD16 expression than patients on DMARDs.
Therefore, CD14+CD16+ circulating blood monocytes may represent an appropriate biomarker to assess RA disease activity along with DAS28 and US7 scores. Together, these three parameters may represent a better indicator for evaluating therapy efficacy.