Improvement of flow cytometric analysis of basophil activation inhibition by high histamine dilutions. A novel basophil specific marker: CD 203c

BACKGROUND: Histamine is known to elicit a negative feedback effect on anti-IgE and allergen-induced basophil activation. A series of experiments performed between 1981 and 1995 using a manual method showed biological activity of highly diluted histamine. Most of the experiments used histamine in the range 10(-30) (15C)-10(-36) M (18C). These results were confirmed by automated flow cytometry, but this method is based on the selection of basophils by anti-IgE and analysis of basophil activation by anti-CD 63, showing significant but relatively low inhibition (approximately 14%), insufficient to convince the scientific community of the reality of the phenomenon. OBJECTIVE: We investigated if the use of CD 203c, a basophil specific, earlier marker than CD 63 of the activation cascade, increased the sensitivity of the method, testing two target histamine dilutions, 10(-4) (2C) and 10(-32) M (16C). METHODS: Basophils, obtained from buffy coats, were pre-incubated with the histamine dilutions and activated by two agonists: anti-IgE and fMLP (formyl-methionyl-leucyl-phenylalanine peptide). Basophil activation was stopped with EDTA. The cells were labelled with anti-IgE, anti-CD 13 and anti-CD 14 for basophil selection, and anti-CD 63 and anti-CD 203c for basophil activation. Results were expressed in up-regulation percentage for CD 63 or mean intensity of fluorescence (MFI) for CD 203c. RESULTS: Histamine 10(-4) M (2C) and histamine 10(-32) M (16C) were capable of inhibiting both IgE-dependent (anti-IgE) and IgE-independent (fMLP) basophil activation. The percentage inhibition depended on the activation marker used. The highest inhibition for histamine dilution 16C was observed with CD 203c (38%, P<0.001), approximately half the inhibition observed with histamine 2C (73%). CONCLUSION: These new flow cytometric protocols confirmed that high dilutions of histamine may inhibit basophil activation and that the inhibitory effect is not restricted to IgE-dependent activation. The use of CD 203c instead of CD 63 increased the magnitude of the response.