Eosinophil granule proteins in peripheral blood granulocytes

Eosinophils contain four principal cationic proteins, major basic protein (MBP), eosinophil-derived neurotoxin (EDN), eosinophil cationic protein (ECP), and eosinophil peroxidase (EPO). To determine the quantities of these proteins in granulocytes and whether they are specific to eosinophils, their concentrations in lysates of human granulocytes were measured using specific radioimmunoassays. The effect of different methods for eosinophil lysis on the recovery of the proteins was also studied. Maximal recovery occurred at pH 2 for MBP and pH 5.6 for the other granule proteins. The proteins cosedimented with eosinophils and their concentrations (X̄ ± SEM) in ng/10⁶ eosinophils (and in nM/10⁶ eosinophils) were: MBP, 8,982 ± 611 (641.6); EDN, 3,283 ± 116 (178.4); ECP, 5,269 ± 283 (250.9); and EPO, 12,174 ± 859 (171.5). Basophils from a normal person contained (in ng/10⁶ cells) MBP, 2,374; EDN, 214; ECP, 77; and EPO, 17. Highly purified neutrophils contained (in ng/10⁶ cells) MBP, 3 ± 0.5; EDN, 72 ± 9; and ECP, 50 ± 12. Therefore we conclude that these proteins are mainly expressed in eosinophils, but that certain ones are present in basophils and neutrophils.