In this study, we investigated whether monocyte CD64 (mCD64) expression is correlated with disease activity in patients with adult-onset Still disease (AOSD) and whether it could be used to distinguish between active and inactive disease states.
We reviewed a series of 10 patients with a definite diagnosis of AOSD, recruited from January 2013 to December 2016. We used flow cytometry to quantitatively measure mCD64 expression levels in patients presenting with active and inactive disease states and statistically analyzed the corresponding changes.
The mean ± SD values of mCD64 expression levels in patients with active and inactive disease states were 77,148.3 ± 39,066.3 and 19,225.8 ± 7006.2 molecules/cell, respectively, indicating significantly higher mCD64 expression in the active state than in the inactive state (p = 0.005). Receiver operating characteristic analysis with a cutoff value of 31,796.0 molecules/cell was applied to distinguish active from inactive disease states; the sensitivity and specificity were both 100%. In these patients, only the mCD64 expression levels changed in parallel with disease activity under tocilizumab treatment; other conventional biomarkers measured showed no changes.
Monocyte CD64 expression could be used to clearly distinguish between active and inactive AOSD. Thus, mCD64 could be a promising biomarker for evaluating the disease activity of AOSD, even in patients receiving tocilizumab treatment.