Variations in protein expression related to human eosinophil heterogeneity

In hypereosinophilic patients, eosinophil heterogeneity has been assessed mainly according to morphologic and biologic criteria. In order to investigate the molecular basis of such heterogeneity, biochemical analysis was performed on various eosinophil subpopulations fractionated on metrizamide gradients. Whole cell extracts from purified eosinophils disrupted with a nonionic (NP-40) detergent were successively analyzed by SDS-PAGE and two-dimensional electrophoresis (isoelectric focusing or nonequilibrium pH gradient electrophoresis in the first dimension). Hypodense eosinophils that sediment in the lightest density gradients (18 to 22% metrizamide solution) differed from other purified eosinophils (intermediate and normodense eosinophils respectively collected in 22 to 23% and 23 to 25% metrizamide solutions). Comparative analysis of protein patterns on both monodimensional and bidimensional electrophoresis showed that a basic protein of Mr 51 kDa, present on normodense or intermediate eosinophils, was poorly detected in the case of hypodense eosinophils. In contrast, two other proteins with apparent Mr of about 23 kDa and 41 kDa were exclusively or predominantly identified in these latter cell fractions. Immunochemical analysis with polyclonal antibodies against eosinophil basic proteins and enzymatic assays revealed that the 51-kDa polypeptide could be related to an eosinophil peroxidase-like molecule. In addition, the two proteins detected only in hypodense eosinophils might be related to proteins newly synthesized by in vivo activated eosinophils. Our results suggest that variations in protein expression might represent a good marker of in vivo activation.