Understanding the roles of basophils: breaking dawn

Early studies that used parasite-infected interleukin-4 (IL-4) reporter animals led us to identify basophils as the primary source of IL-4 and hence propose the hypothesis that basophils trigger the development of antigen-specific T helper type 2 (Th2) immune responses in vivo. These findings appeared to resolve a long-standing puzzle underlying Th2 immunity, that is, ‘what is the source of the initial IL-4 necessary for CD4 T-cell differentiation into Th2 effector cells?’. However, results from extensive investigations of the contribution of basophils to Th2 immunity unveiled some controversial data that cast doubt on the initial hypothesis. In this review, the consensus and the controversy regarding the roles of basophils in infection and immunity, as well as outstanding questions for the future, are discussed.     

Sputum basophils from allergic asthmatic patients do not express IL-7Rα that is essential for TSLP signalling

Basophils are crucial in regulating allergic reactions via immediate secretion of multiple mediators upon IgE-induced degranulation. IL-3 regulates the development and activation of human basophils while epithelial cytokine thymic stromal lymphopoietin (TSLP) is another key regulator for murine basophils. Despite association of increased TSLP with exaggerated basophil responses in oesophageal biopsies, the effects of TSLP in regulating human basophil degranulation and activation are under debate. In this study, we aimed to examine whether human basophils responded to TSLP by co-expression of TSLP receptors, TSLPR and IL-7Rα (CD127), upon in vitro activation and in sputum of allergic asthmatic patients. Flow cytometric analysis of fresh basophils from healthy controls revealed no detectable TSLPR and CD127. Further flow cytometric analysis of basophils from healthy controls in vitro stimulated by multiple established basophil modulators for 24 hours showed induction of TSLPR but not CD127 by IL-3 (10 ng/ml), anti-IgE (10 μg/ml) and C5a (50 ng/ml). One-hour stimulation of basophils from allergic asthmatic patients and healthy controls by TSLP (50 ng/ml) with or without IL-3 (10 ng/ml) and anti-IgE (10 μg/ml) had no effect on induction of CD63⁺ degranulated basophils. Similarly, TSLP (50 ng/ml) with or without IL-3 (10 ng/ml) and anti-IgE (10 μg/ml) did not induce IL-4 and IL-13 production by basophils from healthy controls. Further ex vivo analysis revealed that sputum basophils from allergic asthmatic patients did not express CD127. We conclude that human basophils from healthy controls and allergic asthmatic patients do not respond to TSLP as lacking CD127.     

Risk Factors Predicting Severe Asthma Exacerbations in Adult Asthmatics: A Real-World Clinical Evidence

PurposeMinimizing the future risk of asthma exacerbation (AE) is one of the main goals of asthma management. We investigated prognostic factors for risk of severe AE (SAE) in a real-world clinical setting.MethodsThis is an observational study evaluating subjects who were diagnosed with asthma and treated with anti-asthmatic medications from January 1995 to June 2018. Risk factors for SAE were analyzed in 2 treatment periods (during the initial 2 years and the following 3–10 years of treatment) using the big data of electronic medical records.ResultsIn this study, 5,058 adult asthmatics were enrolled; 1,335 (28.64%) experienced ≥ 1 SAE during the initial 2 years of treatment. Female sex, higher peripheral eosinophil/basophil counts, and lower levels of forced expiratory volume in 1 second (FEV1; %) were factors predicting the risk of SAEs (P < 0.001 for all). Higher serum total immunoglobulin E levels increased the risk of SAEs among the patients having ≤ 2 SAEs (P = 0.025). Patients with more frequent SAEs during the initial 2 years of treatment had significantly higher risks of SAEs during the following years of treatment (P < 0.001, for all) (patients with ≥ 4 SAEs, odds ratio [OR], 29.147; those with 3 SAEs, OR, 14.819; those with 2 SAEs, OR, 9.867; those with 1 SAE, OR, 5.116), had higher maintenance doses of systemic steroids, and showed more gradual decline in FEV1 (%) and FEV1/forced vital capacity levels maintained during the following years of treatment (P < 0.001 for all).ConclusionsAsthmatics having risk factors for SAEs (female sex, higher peripheral eosinophil/basophil counts, and lower FEV1) should be strictly monitored to prevent future risk and improve clinical outcomes.     

TLR1-TLR4在人嗜碱性粒细胞中的表达

目的分别在基因和蛋白水平上观察Toll样受体(Tolllikereceptor,TLR)家族成员中的TLR1、TLR2、TLR3和TLR4在人嗜碱性粒细胞系KU812中的表达。方法取1×106细胞,从细胞中提取总RNA后,用RT-PCR检测细胞中mRNA的表达;用抗人TLR1-TLR4单克隆抗体和小鼠同型抗体行免疫荧光染色后,在流式细胞仪上检测TLR1-TLR4蛋白的表达。结果人嗜碱性粒细胞有TLR1-14mRNA的组成型表达。在流式细胞仪检测中,用抗人TLR1-TLR4单克隆抗体染色的细胞,其荧光强度均明显高于同型对照。结论嗜碱性粒细胞中有TLR-TLR4的组成型表达,提示嗜碱性粒细胞可作为一种免疫细胞对病原微生物进行识别。     

Protein kinase C, a coupling element between stimulus and secretion of basophils

Protein kinase C plays a crucial role in the transmission and control of secretory cell membranal signals. This Ca2+ and phospholipid dependent kinase have been isolated and partially purified from histamine secreting rat basophilic leukemia cells (RBL-2H3 line). The tumor promoter 12-O-tetradecanoyl phorbol-13-acetate ester (TPA) directly activated this isolated enzyme. In the intact RBL-2H3 cells, TPA did not significantly affect free intracellular Ca2+ ions concentration or induce secretion. However, at low concentrations it synergistically enhanced secretion induced either by antigen or ionophore. Significantly, at TPA concentrations exceeding 25 ng/ml both the increase in cytosolic free Ca2+ and the ensuing degranulation were inhibited. The synergism between TPA and the ionophore reaches saturation. These findings suggest that free cytosolic Ca2+ and kinase C-mediated protein phosphorylation are synergistically involved in the mediation of the cellular response. Moreover, kinase C appears to play a dual role both in the activation and termination of secretion. The latter is most probably achieved by closure of the Ca2+ channels in the cells.     

Spontaneous histamine release from washed leukocytes and whole blood in atopic and non-atopic individuals

The ability of basophils from patients with allergic rhinitis, extrinsic asthma, chronic idiopathic urticaria and atopic dermatitis to release histamine spontaneously in vitro was studied. Spontaneous release in the presence and absence of 30% D2O was investigated from both washed leukocytes and whole blood. Compared with controls histamine release (HR) from washed leukocytes was significantly enhanced in allergic rhinitis patients only, whereas in the other groups only a certain percentage of patients was found to have high spontaneous HR. In whole blood experiments HR in all groups was within the normal range. Our data indicate that enhanced spontaneous mediator release from washed basophils in vitro does not necessarily prove this mechanism to be of pathophysiological relevance in vivo.     

The size of the disease relevant IgE antibody fraction in relation to 'total-IgE' predicts the efficacy of anti-IgE (Xolair®) treatment

Background:  Some patients with allergic asthma treated with anti-IgE (Xolair^®) do not become symptom free. Better criteria for response assessment than allergy skin tests or IgE determination are needed. The impact of the size of the disease relevant allergen-specific IgE antibody fraction, i.e. the percentage of IgE antibody of total IgE, was evaluated in cat allergic patients treated with the recommended doses of Xolair^®. Results were measured as changes in basophil allergen threshold sensitivity (CD-sens).
Methods:  In a double-blind placebo controlled trial 20 patients with a high (>3.8%) and 18 with a low (<1%) percentage of IgE antibodies to cat were given Xolair^® for 16 weeks and the change in CD-sens was compared to 11 and 10 patients, respectively, in each group receiving placebo.
Results:  The CD-sens dropped significantly in both the high ( P  < 0.001) and low ( P  < 0.001) group on Xolair^® but did not change significantly after placebo. For Xolair^®-treated patients, at the end of the trial there was a highly significant ( P  < 0.001) difference in CD-sens between the high group, where no patients, and the low group, where 13/18 patients, had become negative.
Conclusions:  The currently recommended doses of Xolair^® very efficiently eliminate IgE antibodies if the IgE antibody fraction is <1% of total IgE but has not enough effect on allergen sensitivity if the fraction is >3–4%. Further studies will show if increased doses of Xolair^® would help also these patients, who seem to represent about 1/3 of the patient population.