Neutrophils express CD52. (A) Purified neutrophils (i) and mononuclear cells (ii) were stained with anti-CD16, anti-CD14, and anti-CD52 mAbs. Surface expression of each of these markers in each of the 3 populations (R1 in panel i and R2 and R3 in panel ii) is shown in panels iii through xi. Neutrophils were identified on the basis of size and granularity (i), and by the expression of a CD16^highCD14^low phenotype (iii). In this way, they were differentiated from monocytes (CD16^lowCD14^high, iv) and NK cells (CD16^low CD14^neg, v). Neutrophils express CD52 (vi,ix). T and B lymphocytes express very high levels of CD52 (viii, bottom right quadrant), whereas monocytes (vii,x) and NK cells (viii, top right quadrant) express lower levels. (B) Unseparated leukocytes were stained with various dilutions of an anti-CD52 mAb (clone HI186). Gating on lymphocytes and neutrophils (R1 and R2 in panel i, respectively), the flow cytograms show that CD52 is expressed at lower levels on neutrophils (iii) than on lymphocytes (ii). Similar results were obtained for the anti-CD52 mAb clone YTH34.5 (data not shown). Open histograms represent staining with an anti-CD52 mAb; shaded histograms represent staining with an isotype-matched control mAb of irrelevant specificity. (C) Using CD16 to differentiate neutrophils (CD16^high, ii) from eosinophils (CD16^neg/low, vi), we observed that both granulocyte populations express CD52, with significantly lower expression by neutrophils (ii). Open histograms represent staining with an anti-CD52 mAb; shaded histograms represent staining with an isotype-matched control mAb of irrelevant specificity.