CD200 and systemic lupus erythematosus: In keeping with the increased percentage of cells expressing CD200, the circulating levels of CD200 in SLE patients were also significantly higher than that in HCs (median 142.22, interquartile range 82.26 to 469.29 vs. 76.62, 45.9 to 124.93 pg/ml; P = 0.001).