Brittany Watson

Thymic stromal lymphopoietin: a central regulator of allergic asthma

Introduction: Epithelial cell-derived mediators have emerged as key players for instigating local remodeling and the associated cellular inflammation in asthmatic airways. In particular, the epithelial-derived cytokine, thymic stromal lymphopoietin (TSLP), has been identified as a master switch for allergic inflammation. Areas covered: TSLP is expressed by structural and immune cells at the site of allergen entry in the airways. Stimuli for release of TSLP include common triggers of asthma symptoms, and TSLP levels correlate with disease severity. TSLP regulates helper T cell 2 (Th2) humoral immunity through upregulating OX40L on dendritic cells (DCs), which drives Th2 lymphocytes; however, activation of several other cells by TSLP also supports the development of Th2 inflammation. Animal models of asthma demonstrate that increased levels of TSLP can induce many of the characteristics of asthma. Expert opinion: The work conducted to date supports a critical role of TSLP in the pathogenesis of allergic asthma. The first clinical trial to block the downstream effects of OX40L has shown reduced levels of circulating IgE and airway eosinophils, confirming the importance of TSLP-induced OX40L levels on DCs. Clinical trials with TSLP blockade are underway and will unequivocally confirm whether TSLP is indeed a key driver of allergic inflammation in asthma.

Eculizumab for treatment of asthma.

Introduction: Asthma is an inflammatory disease, which can be exacerbated by stimuli such as viral infections and exposure to allergens. Asthma continues to be a profound public health problem due to asthma exacerbation in a low proportion of patients in need of more effective medications. Areas covered: The C5 complement pathway has been proposed as a new target for the treatment of asthma, supported by clinical observations of increased C5a levels in asthmatic airways, constitutive expression of C5 receptors on bronchial epithelium and smooth muscle cells, and preclinical studies in mice demonstrating inhibition of C5 cleavage reduced established airway inflammation and improves lung function. Eculizumab is a monoclonal antibody, which binds to the complement protein C5, thereby preventing the formation of C5a and C5b-9. The research discussed in this review describes development of eculizumab for the treatment of paroxysmal nocturnal hemoglobinuria and the efficacy of eculizumab on allergen-induced asthmatic responses in a placebo-controlled study. Expert opinion: In an allergen-challenge model of asthma, there was a significant period effect with eculizumab, with inhibition of the late asthmatic response in subjects who received placebo treatment first. Although this study provides some evidence that eculizumab may be effective to attenuate allergen-induced responses, the role of C5 in asthma remains to be clarified.

Reproducibility of Sputum Differential Cell Counts Is not Affected by Squamous Epithelial Cells

Objective. Induced sputum is used to assess markers of inflammation in asthmatic individuals, and sputum cell differential counts provide an outcome to evaluate the presence, type, and degree of inflammation in the airways. Contamination of sputum slides with squamous epithelial cells (SECs) has been reported to adversely affect the reproducibility of sputum cell differential counts; however, this has not been studied in a controlled manner. Excluding sputum slides because of excessive squamous cell contamination can be problematic resulting in under-powering of studies. The aim of this study is to evaluate the effect of SEC contamination and cell dispersion on the reproducibility of differential counts of sputum cells prepared on glass slides. Study Design. A total of 33 sputum samples were induced from 11 subjects with mild asthma under baseline conditions and following an allergen inhalation challenge. Mucoid and salivary portions of each sample were divided and processed in parallel. To evaluate the effect of increasing the proportion of SEC and to evaluate the effect of increasing the number of leukocytes per high power field (HPF), four slides with varying leukocyte numbers and SEC percentages were prepared from each sample by combining and adjusting the volume of cell suspensions derived from mucous and saliva. The four slides were prepared to fall in the following categories: (A) 50 cells/HPF and <20% SEC; (B) 50 cells/HPF and >20% SEC; (C) 100 cells/HPF and <20% SEC; and (D) 100 cells/HPF and >20% SEC. All slides were blinded and counted twice by an experienced observer, and twice by an inexperienced observer. Results. The differential cell counts for eosinophils, macrophages, and neutrophils were highly reproducible under all conditions when enumerated by an experienced observer (ICC > 0.9), and furthermore, SEC contamination did not affect ICC when differential counts were enumerated by an inexperienced observer (ICC > 0.8). Conclusion. Our results demonstrate that slides containing SECs, up to 40% in this study, have reproducible differential cell counts.

Inhibition of Allergen-Induced Basophil Activation by ASM-024, a Nicotinic Receptor Ligand

Background: Nicotinic acetylcholine receptors (nAChRs) were identified on eosinophils and shown to regulate inflammatory responses, but nAChR expression on basophils has not been explored yet. Objective: We investigated surface receptor expression of nAChR α4, α7 and α1/α3/α5 subunits on basophils. Furthermore, we examined the effects of ASM-024, a synthetic nicotinic ligand, on in vitro anti-IgE and in vivo allergen-induced basophil activation. Methods: Basophils were enriched from the peripheral blood of allergic donors and the expression of nAChR subunits and muscarinic receptors was determined. Purified basophils were stimulated with anti-IgE in the presence of ASM-024 with or without muscarinic or nicotinic antagonists for the measurement of CD203c expression and histamine release. The effect of 9 days of treatment with 50 and 200 mg ASM-024 on basophil CD203c expression was examined in the blood of mild allergic asthmatics before and after allergen inhalation challenge. Results: nAChR α4, α7 and α1/α3/α5 receptor subunit expression was detected on basophils. Stimulation of basophils with anti-IgE increased CD203c expression and histamine release, which was inhibited by ASM-024 (10-5 to 10-3 M, p < 0.05). The effect of ASM-024 was reversed in the presence of muscarinic and nicotinic antagonists. In subjects with mild asthma, ASM-024 inhalation significantly inhibited basophil CD203c expression measured 24 h after allergen challenge (p = 0.03). Conclusion: This study shows that ASM-024 inhibits IgE- and allergen-induced basophil activation through both nicotinic and muscarinic receptors, and suggests that ASM-024 may be an efficacious agent for modulating allergic asthma responses.

Evaluation of peroxisome proliferator-activated receptor agonists on interleukin-5-induced eosinophil differentiation

Peroxisome proliferator‐activated receptor (PPAR) agonists have been suggested as novel therapeutics for the treatment of inflammatory lung disease, such as allergic asthma. Treatment with PPAR agonists has been shown to inhibit airway eosinophilia in murine models of allergic asthma, which can occur through several mechanisms including attenuated generation of chemoattractants (e.g. eotaxin) and decreased eosinophil migrational responses. In addition, studies report that PPAR agonists can inhibit the differentiation of several cell types. To date, no studies have examined the effects of PPAR agonists on interleukin‐5 (IL‐5) ‐induced eosinophil differentiation from haemopoietic progenitor cells. Non‐adherent mononuclear cells or CD34+ cells isolated from the peripheral blood of allergic subjects were grown for 2 weeks in Methocult® cultures with IL‐5 (10 ng/ml) and IL‐3 (25 ng/ml) in the presence of 1–1000 nm PPARα agonist (GW9578), PPARβ/δ agonist (GW501516), PPARγ agonist (rosiglitazone) or diluent. The number of eosinophil/basophil colony‐forming units (Eo/B CFU) was quantified by light microscopy. The signalling mechanism involved was assessed by phosphoflow. Blood‐extracted CD34+ cells cultured with IL‐5 or IL‐5 + IL‐3 formed Eo/B CFU, which were significantly inhibited by rosiglitazone (100 nm, P < 0·01) but not GW9578 or GW501516. In addition, rosglitazone significantly inhibited IL‐5‐induced phosphorylation of extracellular signal‐regulated kinase 1/2. We observed an inhibitory effect of rosiglitazone on eosinophil differentiation in vitro, mediated by attenuation of the extracellular signal‐regulated kinase 1/2 signalling pathway. These findings indicate that the PPARγ agonist can attenuate tissue eosinophilia by interfering with local differentiative responses.