The aim of this study was to assess the expression of CD23 on peripheral blood B-cells, and its in vitro modulation by recombinant human interferon-gamma (IFN-gamma) in phytohaemagglutinin-(PHA) or recombinant human interleukin-4 (IL-4)-stimulated cultures in atopic patients with Dermatophagoides pteronyssinus hypersensitivity and in healthy non-atopic subjects. Atopic patients with asthma not receiving allergen-specific immunotherapy (n = 21) were studied and further compared with a group of atopic subjects with asthma under allergen-specific immunotherapy (n = 21). They were age-(+/- 5 yr) and sex-matched. The results were also compared with those obtained in the non-atopic group (n = 11). CD23 expression on B-lymphocytes and its modulation were analyzed by flow cytometry using conjugated monoclonal antibodies with a double immunofluorescence method. Atopic patients had an increase in the percentage of B-cells expressing CD23 in peripheral blood. Phytohaemagglutinin and IL-4 induced a rise in the percentage of CD23-positive B-cells in both atopic groups and non-atopic subjects. Phytohaemagglutinin provoked an increase in the intensity of CD23 expression on B-cells from stimulated cultures in all groups, while IL-4 only produced a significant increase in atopic patients. The presence of IFN-gamma decreased the CD23 expression on B-cells in PHA-stimulated culture of atopic patients, whereas it caused an increase in CD23 expression in the non-atopic group. Furthermore, the presence of IFN-gamma in IL-4-stimulated cultures induced a decrease in CD23 expression on B-cells in all cases.(ABSTRACT TRUNCATED AT 250 WORDS)