Upregulation of CD16− monocyte subsets in systemic lupus erythematous patients

Monocytes are an important component in the innate immune system. However, studies to date have failed to conclude whether their levels are altered in patients with systemic lupus erythematosus (SLE). We applied the cytodiff counting method and comprehensively measured the circulating levels of distinct white blood cell (WBC) subsets, including CD16+, CD16−, and total monocytes, in 61 SLE patients as well as in 203 age-matched healthy controls (HCs). The absolute number of CD16− monocytes, total monocytes, immature granulocytes, mature neutrophils, total neutrophils, and T cell blasts was significantly higher, that of non-cytotoxic T lymphocytes, cytotoxic T + NK lymphocytes, T + NK lymphocytes, total lymphocytes, basophils, and eosinophils significantly lower (all p < 0.05), but that of CD16+ monocytes, B lymphocytes, B cell blasts, non-B and non-T cell blasts, and total blasts was not statistically different in SLE patients, as compared to HC. Specifically, among all subsets examined, the percentage of CD16− monocytes and total monocytes was the only one that could discriminate active SLE from quiescent SLE (p = 0.033 and 0.026, respectively). SLE patients with lupus nephritis were also associated with higher levels of circulating CD16− monocytes and total monocytes, in comparison with that of controls (both p < 0.0001). This study suggests the significance of distinct WBC subsets, particularly the differential regulations of monocyte subsets, in the pathogenesis and development of SLE.