Eosinophils are able to secrete exosomes that have an undefined role in asthma pathogenesis. We hypothesized that exosomes released by eosinophils autoregulate and promote eosinophil function. Eosinophils of patients with asthma (n = 58) and healthy volunteers (n = 16) were purified from peripheral blood, and exosomes were isolated and quantified from eosinophils of the asthmatic and healthy populations. Apoptosis, adhesion, adhesion molecules expression, and migration assays were performed with eosinophils in the presence or absence of exosomes from healthy and asthmatic individuals. Reactive oxygen species (ROS) were evaluated by flow cytometry with an intracellular fluorescent probe and nitric oxide (NO) and a colorimetric kit. In addition, exosomal proteins were analyzed by mass spectrometry. Eosinophil-derived exosomes induced an increase in NO and ROS production on eosinophils. Moreover, exosomes could act as a chemotactic factor on eosinophils, and they produced an increase in cell adhesion, giving rise to a specific augmentation of adhesion molecules, such as ICAM-1 and integrin α2. Protein content between exosomes from healthy and asthmatic individuals seems to be similar in both groups. In conclusion, we found that exosomes from the eosinophils of patients with asthma could modify several specific eosinophil functions related to asthma pathogenesis and that they could contribute fundamentally to the development and maintenance of asthma.

Intercellular communication is crucial to the immune system response. In the recent years the discovery of exosomes has changed the way immune response orchestration was understood. Exosomes are able to operate as independent units that act as mediators in both physiological and pathological conditions. These structures contain proteins, lipidic mediators, and nucleic acids, and notoriously include microRNAs (miRNAs). miRNAs are short RNA sequences (around 19–22 nucleotides) with a high phylogenetic conservation and can partially or totally regulate multiple mRNAs, inhibiting protein synthesis. In respiratory diseases such as asthma and allergic sensitization, exosomes released by several cell types and their specific content perform crucial functions in the development and continuation of the pathogenic mechanisms. Released exosomes and miRNAs inside them have been found in different types of clinical samples, such as bronchoalveolar lavage fluids and sputum supernatants, providing new data about the environmental factors and mediators that participate in the inflammatory responses that lead to the exacerbation of asthma. In this review, we summarize our current knowledge of the role of exosomes and miRNAs in asthma and allergic sensitization, paying attention to the functions that both exosomes and miRNAs are described to perform through the literature. We review the effect of exosomes and miRNAs in cells implicated in asthma pathology and the genes and pathways that they modify in them, depicting how their behavior is altered in disease status. We also describe their possible repercussion in asthma diagnosis through their possible role as biomarkers. Therefore, both exosomes and miRNAs can be viewed as potential tools to be added to the arsenal of therapeutics to treat this disease.