Elevation of soluble CD23 in serum from patients with blood eosinophilia

The levels of soluble CD23 (sCD23) were evaluated by a two-site immunoradiometric assay in the sera of 41 patients with eosinophilia-associated disorders and 20 normal subjects. We observed that, in the absence of treatment, sCD23 levels were elevated in patients with eosinophilia-associated Gleich's syndrome, IgA deficiency, T lymphoma or hypereosinophilic syndrome (HES), but not in patients with a parasitic infection. A significant reduction in the sCD23 levels was found after treatment, with a parallel decrease in eosinophil counts and in sCD25 levels, a marker of disease activity in HES. The lack of increase in membrane CD23+ B cells in eosinophilic patients together with the detection of sCD23 in eosinophil supernatants suggest that activated eosinophils present in eosinophilia-associated disorders can release soluble molecules cross-reacting with CD23. In conclusion, our results suggest that eosinophils themselves can represent one cellular source of sCD23. These findings are not only basic but also of clinical interest.