Most human blood basophils respond to FcεRI cross-linking by releasing histamine and other inflammatory mediators. Basophils that do not degranulate after anti-IgE challenge, known as “nonreleaser” basophils, characteristically have no or barely detectable levels of the Syk tyrosine kinase. The true incidence of the nonreleaser phenotype, its relationship (if any) to allergic asthma, and its molecular mechanism are not well understood. In this study, we report statistical analyses of degranulation assays performed in 68 control and 61 asthmatic subjects that establish higher basal and anti-IgE-stimulated basophil degranulation among the asthmatics. Remarkably, 28% of the control group and 13% of the asthmatic group were nonreleasers for all or part of our 4-year long study and cycling between the releaser and nonreleaser phenotypes occurred at least once in blood basophils from 8 (of 8) asthmatic and 16 (of 23) control donors. Microarray analysis showed that basal gene expression was generally lower in nonreleaser than releaser basophils. In releaser cells, FcεRI cross-linking up-regulated >200 genes, including genes encoding receptors (the FcεRI α and β subunits, the histamine 4 receptor, the chemokine (C-C motif) receptor 1), signaling proteins (Lyn), chemokines (IL-8, RANTES, MIP-1α, and MIP-1β) and transcription factors (early growth response-1, early growth response-3, and AP-1). FcεRI cross-linking induced fewer, and quite distinct, transcriptional responses in nonreleaser cells. We conclude that “nonreleaser” and “cycler” basophils represent a distinct and reversible natural phenotype. Although histamine is more readily released from basophils isolated from asthmatics than controls, the presence of nonreleaser basophils does not rule out the diagnosis of asthma.

Cross-linking the high-affinity IgE receptor, FcεRI, on mast cells activates signaling pathways leading to the release of preformed inflammatory mediators and the production of cytokines and chemokines associated with allergic disorders. Bone marrow-derived mast cells (BMMCs) from Lyn-deficient (Lyn−/−) mice are hyperresponsive to FcεRI cross-linking with multivalent Ag. Previous studies linked the hyperresponsive phenotype in part to increased Fyn kinase activity and reduced SHIP phosphatase activity in the Lyn−/− BMMCs in comparison with wild-type (WT) cells. In this study, we compared gene expression profiles between resting and Ag-activated WT and Lyn−/− BMMCs to identify other factors that may contribute to the hyperresponsiveness of the Lyn−/− cells. Among genes implicated in the positive regulation of FcεRI signaling, mRNA for the tyrosine kinase, Fyn, and for several proteins contributing to calcium regulation are more up-regulated following Ag stimulation in Lyn−/− BMMCs than in WT BMMCs. Conversely, mRNA for the low-affinity IgG receptor (FcγRIIB), implicated in negative regulation of FcεRI-mediated signaling, is more down-regulated in Ag-stimulated Lyn−/− BMMCs than in WT BMMCs. Genes coding for proinflammatory cytokines and chemokines (IL-4, IL-6, IL-13, CSF, CCL1, CCL3, CCL5, CCL7, CCL9, and MIP1β)are all more highly expressed in Ag-stimulated Lyn−/− mast cells than in WT cells. These microarray data identify Lyn as a negative regulator in Ag-stimulated BMMCs of the expression of genes linked to FcεRI signaling and also to the response pathways that lead to allergy and asthma.