['CD23 plays an important role in IgE regulation. The modulation of CD23 expression during specific immunotherapy (SIT) has been described previously. In the present study, we investigated in detail the effects of complete birch pollen allergen extract (BPA) on CD23 expression of peripheral blood mononuclear cells (PBMCs) in vitro.', 'PBMCs from 14 birch pollen-allergic (bp-allergic) patients and eight non-bp-allergic controls were stimulated with IL-4 and increasing doses of BPA. CD23 expression on monocytes and B cells was measured by flow cytometry; sCD23 release and the levels of IFN-gamma and IL-10 secretion were determined by ELISA. To analyse the mechanisms on CD23 expression in more detail, neutralizing anti-IFN-gamma and anti-IL-10 antibodies were added to IL-4 and BPA-stimulated cultures.', 'IL-4 induced CD23 expression on B cells and on monocytes and sCD23 release in the bp-allergic and non-bp-allergic groups. The addition of BPA to IL-4-stimulated PBMC decreased CD23 expression significantly and dose-dependently on B cells in both groups. CD23 expression on monocytes was also decreased in both groups after the addition of BPA, but higher doses were required in the non-bp-allergic population. IL-4-induced sCD23 release was also significantly decreased after the addition of BPA. IFN-gamma and IL-10 were induced by BPA in both the bp-allergic and non-bp-allergic groups. The addition of neutralizing anti-IFN-gamma antibodies increased CD23 expression on B cells, which were stimulated with IL-4 and BPA, but had no effect on monocytes, whereas the addition of anti-IL-10 antibodies increased CD23 expression on monocytes but not on B cells.'] Is allergen-mediated modulation of CD23 expression interferon-gamma and interleukin-10 dependent in allergic and non-allergic individuals?