FCGR1A and systemic lupus erythematosus: Although circulating monocytes from SLE patients also uniformly expressed FcγRI/CD64 (Figure 1a, bottom), quantification of FcγRI/CD64 expression showed a significantly higher mean fluorescence intensity in SLE patients compared with healthy control individuals (521 ± 21 versus 319 ± 22; P < 0.001, Student's t test).