Characteristics of an anti‐eosinophil monoclonal antibody that recognizes granulocytes from patients with blood eosinophilia but not from subjects without eosinophilia

SUMMARY To investigate cell surface antigens of activated human cosinophils using monoclonal antibodies, we established a murine anti‐human eosinophil monoclonal antibody AE500 by immunizing with blood cosinophils from patients with idiopathic hypereosinophilic syndrome (HES) and characterized the reactivity to a variety of human leucocytes by a fluorescence‐activated cell sorter. AE500 reacted with blood cosinophils and neutrophils in nine out of 11 patients with marked eosinophilia (≥ 2500/μI) (seven with idiopathic eosinophilia including HES and two with asthma), but not with those in asthmatic patients with mild eosinophilia ( n = 10) or in healthy subjects ( n = 8). AE500 did not react with blood lymphoyctcs. monocytes or platelets. AESOO did not react with human myeloid or lymphoid cell lines, including eosinophilic leukemia cell lines EOL‐I and EOL‐3. The reactivity of AE500 to blood eosinophils and neutrophils in patients with marked eosinophilia changed in relation to blood eosinophil counts and prednisolone therapy. In addition, the reactivity of AE500 to blood eosinophils was increased in three out of four AE500‐positive eosinophils by the incubation of the cells with granulocyte‐macrophagc colony‐stimulating factor (GM‐CSF) at 37 C for 30 min. but not with interleukin 3 or interlcukin‐5. These results suggest that the anti‐eosinophil antibody AE500 detects a cell surface antigen expressed on blood granulocytes in a hypercosinophilic state. This antieosinophil antibody would be useful for analysing the mechanism of eosinophilia.