Eosinophils play a key role in airway inflammation in many diseases, such as allergic and non-allergic asthma, chronic rhinosinusitis with nasal polyps, and chronic obstructive pulmonary disease. In these chronic disabling conditions, eosinophils contribute to tissue damage, repair, remodeling, and disease persistence through the production a variety of mediators. With the introduction of biological drugs for the treatment of these respiratory diseases, the classification of patients based on clinical characteristics (phenotype) and pathobiological mechanisms (endotype) has become mandatory. This need is particularly evident in severe asthma, where, despite the great scientific efforts to understand the immunological pathways underlying clinical phenotypes, the identification of specific biomarkers defining endotypes or predicting pharmacological response remains unsatisfied. In addition, a significant heterogeneity also exists among patients with other airway diseases. In this review, we describe some of the immunological differences in eosinophilic airway inflammation associated with severe asthma and other airway diseases and how these factors might influence the clinical presentation, with the aim of clarifying when eosinophils play a key pathogenic role and, therefore, represent the preferred therapeutic target.

Episodic angioedema with eosinophilia (EAE) (Gleich’s syndrome) is a rare disease characterized by hypereosinophilia (up to 95 × 10⁹ cells/L), recurrent episodes of angioedema, urticaria, weight gain, and fever, that occur at periodical intervals (usually every 3–4 weeks). The exact etiology of EAE is still unclear, but both eosinophils and abnormalities of cytokines homeostasis seem to play a pivotal role in the pathogenesis of the disease. In particular, the cyclic elevation of serum interleukin-5 before the increase in eosinophil count has been reported. Herein, we performed a broad literature review and report the case of a thirty-two-year-old woman with a two-year history of cyclic angioedema attacks, urticaria, periodic weight gain, and severe hypereosinophilia, diagnosed with EAE and treated with oral corticosteroids. Describing the most relevant clinical features of EAE reported so far in the literature, we aim to provide physicians with some useful tools to help them deal with this disease. In addition, we aim to raise awareness about this rare condition in which approved diagnostic classification criteria are currently missing.

A relationship is emerging between SARS-CoV-2 infections and ANCA-associated vasculitis (AAV) because: (i) the pulmonary involvement of COVID-19 may mimic that observed in patients with AAV; (ii) the two diseases may occur together; (iii) COVID-19 may trigger AAV. However, few cases of AAV have been identified so far in COVID-19 patients. To define the frequency of ANCA autoimmunity in patients with SARS-CoV-2 infection, we analyzed the serum ANCAs and the serum PR3 and MPO antigens by immunoassays in 124 adult patients with a diagnosis of SARS-CoV-2 infection (16 were asymptomatic and 108 were hospitalized) and 48 control subjects. The serum ANCAs were significantly higher in the hospitalized patients compared with either the controls or the asymptomatic patients and increased with the progression of the COVID-19 severity. After one week of hospitalization, the values were significantly lower. In contrast, no differences emerged among the controls, asymptomatic and hospitalized patients for the PR3 and MPO serum levels. None of the patients had clinical signs of AAV with the exception of a severe pulmonary involvement. Further studies are necessary to define whether the increase in the serum ANCAs might mask subclinical vasculitis in a percentage of patients with SARS-CoV-2 infection or it is an epiphenomenon of SARS-CoV-2 infection with no clinical manifestations.

Profound clinical differences between the first and second waves of COVID-19 were observed in Europe. Nitric oxide (NO) may positively impact patients with Severe Acute Respiratory Syndrome CoronaVirus-2 (SARS-CoV-2) infection. It is mainly generated by inducible nitric oxide synthase (iNOS). We studied serum iNOS levels together with serum interleukin (IL)-6 and IL-10 in patients with SARS-CoV-2 infection in the first wave (n = 35) and second wave (n = 153). In the first wave, serum iNOS, IL-6, IL-10 levels increased significantly, in line with the World Health Organization (WHO) score severity, while in the second wave, iNOS did not change with the severity. The patients of the second wave showed lower levels of iNOS, IL-6, and IL-10, as compared to the corresponding subgroup of the first wave, suggesting a less severe outcome of COVID-19 in these patients. However, in the severe patients of the second wave, iNOS levels were significantly lower in patients treated with steroids or azithromycin before the hospitalization, as compared to the untreated patients. This suggests an impairment of the defense mechanism against the virus and NO-based therapies as a potential therapy in patients with low iNOS levels.