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Background: Basophils and mast cells are important initiator/effector cells capable of rapidly responding to IgE-mediated stimulation, but the precise mechanisms regulating their functions in vivo have not been fully identified. In this study, we assessed whether low levels of antigen can modulate activation of basophils and mast cells., Methods: Human basophils and cultured mast cells were pretreated with low concentrations of anti-FcεRI α-chain mAb (CRA-1 mAb), and their cell functions were assessed., Results: Basophils preincubated with CRA-1 mAb at as low as 1 ng/ml for 1 h showed significantly enhanced degranulation in response to various secretagogues such as MCP-1, FMLP, leukotriene B4 and Ca ionophore A23187. FMLP-induced leukotriene C4 production by basophils was also enhanced by CRA-1 mAb pretreatment. Degranulation was further enhanced when CRA-1 mAb-pretreated basophils were additionally treated with IL-3, IL-33 or leptin before stimulation with MCP-1. Priming by subthreshold CRA-1 mAb was a slow process, since 1 h of pretreatment was needed for maximal enhancement. Basophil priming also resulted from preincubation with subthreshold doses of an allergen, Der f 2. In parallel mAb experiments, CRA-1 mAb showed weak priming effects on human umbilical cord blood-derived cultured mast cells; a higher dose, 100 ng/ml, was necessary for this priming., Conclusion: These results indicate that subthreshold doses of CRA-1 mAb or allergens can prime basophils and induce exaggerated responses to various IgE-independent stimuli. This may be a potentially important mechanism that explains environmental allergen-induced exacerbation of IgE-mediated allergic diseases such as asthma., (Copyright © 2013 S. Karger AG, Basel.)

Background: Basophils are thought to play pivotal roles in the pathogenesis of allergic reactions, but their roles in inflammation associated with systemic abnormalities such as metabolic disorders remain largely unknown. Advanced glycation end products (AGEs) are potentially important substances produced in high-glucose disease conditions. In this in vitro study, we investigated whether the biological functions of human basophils can be influenced by AGEs., Methods: We analyzed the effects of AGEs on various functions and markers of human basophils, including CD11b expression, apoptosis, degranulation, and cytokine production., Results: Flow cytometric analysis indicated that the level of the receptor for AGEs (RAGE) on the surface of freshly isolated basophils was very low but was clearly upregulated by IL-3. Apoptosis of basophils was induced by high concentrations of glycated albumin. Although glycated albumin failed to affect the level of surface CD11b expression or to trigger degranulation or production of IL-4 and IL-13 in basophils, it dose-dependently induced IL-6 and IL-8 secretion., Conclusions: AGEs seem to act on human basophils; they suppress the cells' longevity but elicit secretion of inflammatory cytokines. Through these biological changes, basophils might play some roles in inflammatory conditions associated with metabolic disorders presenting elevated levels of AGEs., (Copyright © 2011 S. Karger AG, Basel.)

Background: Japanese cedar pollen is by far the most important cause of allergic rhinitis in Japan. In this study, we assessed the induction of blocking antibody during specific immunotherapy (SIT) using a recently standardized allergen extract from Japanese cedar pollen., Methods: Basophils from nonallergic subjects were passively sensitized with serum samples prepared from pollinosis patients before and after SIT; all patients showed good clinical efficacy. The cells were then stimulated with the standardized allergen, and histamine release was measured. In most experiments, the basophil stimulation buffer contained 1% serum., Results: Pollinosis patients' sera obtained both before and after SIT showed essentially similar sensitizing capacity for basophils. Basophil degranulation in response to a relatively low concentration of pollen extract was effectively suppressed by addition of post-SIT serum samples, indicating the presence of blocking antibody. The blocking antibody was IgG, and its potency varied widely among the donor patients., Conclusions: The standardized allergen extract from Japanese cedar pollen is useful not only for clinical application in SIT, but also for testing for induction of blocking antibody during SIT., (Copyright 2008 S. Karger AG, Basel.)

Surface-expressed CD69 is a recently recognized activation marker for basophils and is reported to be strongly induced in vitro by IL-3. In this study, we investigated whether IgE- and high-affinity receptor for IgE (FcepsilonRI)-dependent stimuli can affect basophil CD69 expression. Highly purified basophils were cultured for 24 h in the presence of anti-FcepsilonRI alpha-chain mAb, CRA-1 and IL-3, and surface CD69 expression was analyzed by flow cytometry. CRA-1 mAb at 1 ng/ml or lower concentrations, levels too low to provoke direct histamine release, dose-dependently enhanced surface CD69 expression in the presence of IL-3, although low-dose CRA-1 mAb failed to induce CD69 expression in the absence of IL-3. Recombinant Der f 2 at 10 to 100 pg/ml enhanced CD69 levels in the presence of IL-3 in basophils from mite-sensitive subjects. These results suggest that allergens may influence basophil CD69 expression even when the levels of the antigens are too low to trigger direct degranulation. Upregulated CD69 expression on locally accumulated basophils in bronchial asthma may be attributed at least in part to a combination of local cytokines, especially IL-3, plus exposure to low levels of IgE-crosslinking allergens.

We investigated the expression and function of a panel of Toll-like receptors (TLRs) in human basophils. Basophil preparations constitutively expressed TLR2, TLR4, TLR9 and TLR10 mRNAs (TLR4 > TLR2 >> TLR9, TLR10). Although TLR mRNA expression in basophils was generally less prominent compared with those in neutrophils and monocytes, basophils expressed significantly higher levels of TLR2 and TLR4 mRNA than eosinophils. Various TLR ligands (Pam3Cys-Ser-Lys4, poly I:C, lipopolysaccharide, R-848, CpG DNA) were tested, but none affected the expression level of adhesion molecule CD11b or the viability of freshly purified basophils. On the other hand, when basophils were pretreated with interferon-gamma before stimulation with TLR ligands, only the TLR4 ligand, lipopolysaccharide, upregulated CD11b expression. However, the surface levels of TLR2 and TLR4 on the interferon-gamma-treated basophils showed no obvious changes. These results suggest that TLR4 on basophils may be involved in the pathogenesis of infection-induced exacerbation of allergic inflammation by modulating basophil functions., (Copyright 2006 S. Karger AG, Basel.)