The release of basogranulin in response to IgE-dependent and IgE-independent stimuli: Validity of basogranulin measurement as an indicator of basophil activation

Background: Basogranulin, the novel basophil granule protein recognized by the monoclonal antibody BB1, can be released by stimulation with anti-IgE antibody or calcium ionophore. However, the kinetics and regulation of its secretion are unknown. Objective: We quantified basogranulin and histamine release in response to a range of stimuli to assess whether basogranulin secretion is a reliable marker of basophil activation. Methods: Isolated peripheral blood basophils were stimulated with anti-IgE antibody, calcium ionophore, N-formyl-Met-Leu-Phe, and complement C5a. The released basogranulin and histamine were quantified by dot blotting with BB1 and a fluorometric method, respectively. Basogranulin localization was confirmed by flow cytometry. Results: Both basogranulin and histamine displayed a bell-shaped response curve when basophils were challenged with anti-IgE. Half-maximal release occurred within 30 seconds. Basogranulin levels were maximal by 15 minutes, whereas those for histamine continued increasing to 30 minutes. Wortmannin, a PI3-K inhibitor, suppressed the release of both mediators. Basophils from donors with the nonreleaser phenotype secreted neither mediator in response to anti-IgE. Non-IgE-dependent stimuli released both mediators in parallel in a concentration-dependent manner. The correlation between the relative amounts of each mediator released was highly significant (r = .901, P < .0001, n = 87). Flow cytometry revealed that some of the secreted basogranulin adhered to the cell surface. Conclusions: Basogranulin is secreted along with histamine in response to both Fc epsilon R I-related and unrelated stimuli. It is therefore a valid marker of basophil activation and could provide the basis for an immunoassay that distinguishes between basophil and mast cell activation.