Immunomodulatory function of surfactant protein D in eosinophilic asthma

Bacterial Extracellular Vesicles: A Candidate Molecule for the Diagnosis and Treatment of Allergic Diseases

Extracellular vesicles (EVs) are an end product released from almost all living cells such as eukaryotic cells and bacteria. These membrane vesicles containing proteins, lipids, and nucleic acids are mainly involved in intracellular communications through the transfer of their components from donor to acceptor cells. Moreover, EVs have been implicated in many functions in response to environmental changes, contributing to health and disease; bacterial EVs depending on their specific parental bacterium have diverse effects on immune responses to play a beneficial or pathogenic role in patients with various allergic and immunologic diseases. As bacterial EVs are a completely new area of investigation in this field, we highlight our current understanding of bacterial EVs and discuss their diagnostic and therapeutic potentials (as immunomodulators) for targeting asthma and atopic dermatitis.

Immunologic Basis of Type 2 Biologics for Severe Asthma

Asthma is a chronic airway inflammatory disease characterized by reversible airway obstruction and airway hyperreactivity to various environmental stimuli, leading to recurrent cough, dyspnea, and wheezing episodes. Regarding inflammatory mechanisms, type 2/eosinophilic inflammation along with activated mast cells is the major one; however, diverse mechanisms, including structural cells-derived and non-type 2/neutrophilic inflammations are involved, presenting heterogenous phenotypes. Although most asthmatic patients could be properly controlled by the guided treatment, patients with severe asthma (SA; classified as a treatment-refractory group) suffer from uncontrolled symptoms with frequent asthma exacerbations even on regular anti-inflammatory medications, raising needs for additional controllers, including biologics that target specific molecules found in asthmatic airway, and achieving the precision medicine for asthma. This review summarizes the immunologic basis of airway inflammatory mechanisms and current biologics for SA in order to address unmet needs for future targets.

Sex Differences in Airway Remodeling and Inflammation: Clinical and Biological Factors

Asthma is characterized by an increase in the contraction and inflammation of airway muscles, resulting in airflow obstruction. The prevalence of asthma is lower in females than in males until the start of puberty, and higher in adult women than men. This sex disparity and switch at the onset of puberty has been an object of debate among many researchers. Hence, in this review, we have summarized these observations to pinpoint areas needing more research work and to provide better sex-specific diagnosis and management of asthma. While some researchers have attributed it to the anatomical and physiological differences in the male and female respiratory systems, the influences of hormonal interplay after puberty have also been stressed. Other hormones such as leptin have been linked to the sex differences in asthma in both obese and non-obese patients. Recently, many scientists have also demonstrated the influence of the sex-specific genomic framework as a key player, and others have linked it to environmental, social lifestyle, and occupational exposures. The majority of studies concluded that adult men are less susceptible to developing asthma than women and that women display more severe forms of the disease. Therefore, the understanding of the roles played by sex- and gender-specific factors, and the biological mechanisms involved will help develop novel and more accurate diagnostic and therapeutic plans for sex-specific asthma management.

Association of serum surfactant protein D and SFTPD gene variants with asthma in Danish children, adolescents, and young adults

BACKGROUND

Surfactant Protein D (SP-D) is a pattern recognition molecule belonging to the family of collectins expressed in multiple human organ systems, including the lungs. Previous studies have shown that SP-D levels in bronchoalveolar lavage samples decrease and serum levels increase in patients suffering from asthma, possibly due to a combination of induced SP-D synthesis and decreased air-blood barrier integrity. The aims of this study were to investigate whether serum levels of SP-D and common variants in the SP-D gene were associated with asthma in adolescents and young adults.

METHODS

Prospective observational study including 449 adolescents and young adults (age 11-27 years) previously diagnosed with asthma during a 2-year period from 2003 to 2005 (0-16 years). At follow-up from 2016 to 2017, 314 healthy controls with no history of asthma were recruited. Serum SP-D was analyzed on samples obtained at baseline as well as samples obtained at follow-up. SP-D genotyping was performed for rs721917, rs2243639, and rs3088308.

RESULTS

No differences were found in mean levels of sSP-D and SFTPD genotype among subjects with current asthma, no current asthma, and controls. Serum SP-D and SFTPD genotype were not associated with any clinical parameters of asthma. Furthermore, baseline sSP-D was not associated with asthma at follow-up.

CONCLUSION

Serum surfactant protein D and common SP-D gene variants were not associated with asthma in Danish adolescents and young adults with mild to moderate asthma. Serum surfactant protein D did not demonstrate any value as a clinical biomarker of asthma.

Emerging Biomarkers Beyond Leukotrienes for the Management of Nonsteroidal Anti-inflammatory Drug (NSAID)-Exacerbated Respiratory Disease

Nonsteroidal anti-inflammatory drug (NSAID)-exacerbated respiratory disease (NERD) is a unique condition characterized by aspirin/NSAID hypersensitivity, adult-onset asthma, and/or chronic rhinosinusitis with nasal polyps. Arachidonic acid metabolism dysregulation and intense eosinophilic/type 2 inflammation are central mechanisms in NERD. Studies have been conducted on various biomarkers, and urinary leukotriene E4 is considered the most available biomarker of NERD. However, the pathophysiology of NERD is heterogeneous and complex. Epithelial cells and platelets can interact with immune cells in NERD, and novel biomarkers related to these interactions have recently been investigated. We summarize emerging novel biomarkers of NERD and discuss their roles in the management of NERD.

Effect of TGF-β1 on eosinophils to induce cysteinyl leukotriene E4 production in aspirin-exacerbated respiratory disease

Cysteinyl leukotriene (cysLT) overproduction and eosinophil activation are hallmarks of aspirin-exacerbated respiratory disease (AERD). However, pathogenic mechanisms of AERD remain to be clarified. Here, we aimed to find the significance of transforming growth factor beta 1 (TGF-β1) in association with cysteinyl leukotriene E4 (LTE4) production, leading to eosinophil degranulation. To evaluate levels of serum TGF-β1, first cohort enrolled AERD (n = 336), ATA (n = 442) patients and healthy control subjects (HCs, n = 253). In addition, second cohort recruited AERD (n = 34) and ATA (n = 25) patients to investigate a relation between levels of serum TGF-β1 and urinary LTE4. The function of TGF-β1 in LTE4 production was further demonstrated by ex vivo (human peripheral eosinophils) or in vivo (BALB/c mice) experiment. As a result, the levels of serum TGF-β1 were significantly higher in AERD patients than in ATA patients or HCs (P = .001; respectively). Moreover, levels of serum TGF-β1 and urinary LTE4 had a positive correlation (r = 0.273, P = .037). In the presence of TGF-β1, leukotriene C4 synthase (LTC4S) expression was enhanced in peripheral eosinophils to produce LTE4, which sequentially induced eosinophil degranulation via the p38 pathway. When mice were treated with TGF-β1, significantly induced eosinophilia with increased LTE4 production in the lung tissues were noted. These findings suggest that higher levels of TGF-β1 in AERD patients may contribute to LTE4 production via enhancing LTC4S expression which induces eosinophil degranulation, accelerating airway inflammation.

Biomarkers for Severe Asthma: Lessons From Longitudinal Cohort Studies

Severe asthma (SA) is a heterogeneous disease characterized by uncontrolled symptoms, frequent exacerbations, and lung function decline. The discovery of phenotypes and endotypes of SA significantly improves our understanding of its pathophysiology and allows the advent of biologics blocking multiple molecular targets. The advances have mainly been made in type 2-high asthma associated with elevated type 2 inflammatory biomarkers such as immunoglobulin E (IgE), interleukins (IL)-4, IL-5, and IL-13. Previous clinical trials have demonstrated that type 2 biomarkers, including blood/sputum eosinophils and the fraction of exhaled nitric oxide (FeNO), were correlated to severe airway inflammation, persistent symptoms, frequent exacerbations, and the clinical efficacy of these biomarkers in predicting treatment outcomes of type 2-targeting biologics. However, it is well known that type 2 inflammation is partially attributable to the pathogenesis of SA. Although some recent studies have suggested that type 2-low and mixed phenotypes of asthma are important contributors to the heterogeneity of SA, many questions about these non-type 2 asthma phenotypes remain to be solved. Consequently, many efforts to investigate and find novel biomarkers for SA have also made in their methods. Many cross-sectional experimental studies in large-scale cohorts and randomized clinical trials have proved their value in understanding SA. More recently, real-world cohort studies have been in the limelight for SA research, which is unbiased and expected to give us an answer to the unmet needs of the heterogeneity of SA.

Pulmonary Surfactants: a New Therapeutic Target in Asthma

Purpose of Review

Lung tissues are highly susceptible to airway inflammation as they are inevitably exposed to inhaled pathogens and allergens. In the lungs, clearance of infectious agents and regulation of inflammatory responses are important for the first-line defense, where surfactants play a role in host defense mechanisms. In this review, clinical significance of pulmonary surfactants in asthma has been highlighted.

Recent Findings

Surfactants, such as surfactant protein A (SP-A) and SP-D released from alveolar epithelium, reduce pathogen infection and control immune-cell activation. Especially, SP-D directly binds to eosinophil surface, leading to inhibition of extracellular trap formation and reduction in airway inflammation. Production of surfactants is commonly determined by both genetic (single nucleotide polymorphisms) and environmental factors influencing processes involved in the development of asthma. In addition, nintedanib (an intracellular inhibitor of tyrosine kinases) could increase SP-D levels and is used in patients with idiopathic pulmonary fibrosis. These findings may provide a possible application of SP-D in asthma.

Summary

Surfactants are key players contributing to host defense through maintaining the immune system. As clinical implications of surfactants involved in asthma have been suggested, further translational studies are needed to apply surfactants as an effective therapeutic target in patients with asthma.

Distinct functions of eosinophils in severe asthma with type 2 phenotype: clinical implications

Asthma is commonly recognized as a heterogeneous condition with a complex pathophysiology. With advances in the development of multiple medications for patients with asthma, most asthma symptoms are well managed. Nevertheless, 5% to 10% of adult asthmatic patients (called severe asthma) are in uncontrolled or partially controlled status despite intensive treatment. Especially, severe eosinophilic asthma is one of the severe asthma phenotypes characterized by eosinophilia in sputum/blood driven by type 2 immune responses. Eosinophils have been widely accepted as a central effector cell in the lungs. Some evidence has demonstrated that persistent eosinophilia in upper and lower airway mucosa contributes to asthma severity by producing various mediators including cytokines, chemokines and granule proteins. Moreover, extracellular traps released from eosinophils have been revealed to enhance type 2 inflammation in patients with severe asthma. These novel molecules have the ability to induce airway inf lammation and hyperresponsiveness through enhancing innate and type 2 immune responses. In this review, we highlight recent insight into the function of eosinophil extracellular traps in patients with severe asthma. In addition, the role of eosinophil extracellular vesicles in severe asthma is also proposed. Finally, current biologics are suggested as a potential strategy for effective management of severe eosinophilic asthma.

Which Factors Associated With Activated Eosinophils Contribute to the Pathogenesis of Aspirin-Exacerbated Respiratory Disease?

Eosinophils have long been recognized as a central effector cell in the lungs of asthmatic patients. They contribute to airway inflammation and remodeling through releasing several molecules such as cytokines, granule proteins, lipid mediators and extracellular traps/vesicles. Repeated evidence reveals that intense eosinophil infiltration in upper and lower airway mucosae contributes to the pathogenesis of aspirin-exacerbated respiratory disease (AERD). Persistent eosinophilia is found to be associated with type 2 immune responses, cysteinyl leukotriene overproduction and eosinophil-epithelium interactions. This review highlights recent findings about key mechanisms of eosinophil activation in the airway inflammation of AERD. In addition, current biologics (targeting type 2 immune responses) were suggested to control eosinophilic inflammation for AERD patients.