Eosinophil Protein X Concentration Is Dependent on Eosinophil Concentration

The relationship between the eosinophil concentration and the serum eosinophil protein X concentration was investigated in 80 subjects. Higher eosinophil counts resulted in obviously increased serum eosinophil protein X concentrations. However, the amount of eosinophil protein X released per eosinophil granulocyte is significantly higher in subjects with lower eosinophil counts. Atopic subjects (N = 19) show a significantly higher eosinophil concentration (p = 0.002) and eosinophil protein X concentration (p = 0.004) and a significantly lower eosinophil protein X/eosinophil ratio (p = 0.02), compared with non-atopic subjects (N = 61). However, there appears to be no difference between the concentration of eosinophil protein X in atopic and non-atopic subjects if the eosinophil concentration is taken into account. When using eosinophil protein X as an indicator of eosinophil activation, for instance in asthmatic subjects, the eosinophil count should also be considered for correct clinical interpretation of results.