MicroRNAs (miRNAs) are small non-coding RNA molecules that are 18–22 nucleotides long and highly conserved throughout evolution. Currently, they are considered one of the fundamental regulatory mechanisms of genes expression. It has been demonstrated that miRNAs are involved in many biologic processes, such as signal transduction, cell proliferation and differentiation, apoptosis and stress responses. More recently, the role of miRNA has also been revealed in numerous immunological and inflammatory disorders, including allergic inflammation. Specific miRNA profiles were demonstrated in asthma, allergic rhinitis and atopic dermatitis. A core set of miRNAs involved in atopic diseases include upregulated miR-21, miR-223, miR-146a, miR-142-5p, miR-142-3p, miR-146b, miR-155 and downregulated let-7 family, miR-193b and miR-375. Most of the involved miRNAs increase secretion of Th2 cytokines (miR-1248, miR-146b), decrease secretion of Th1 cytokines (miR-513-5p, miR-625-5p) or promote differentiation of T cells towards Th2 (miR-21, miR-19a). In asthma miR-140-3p, miR-708 and miR-142-3p play a role in hyperplasia and hypertrophy of bronchial smooth muscle cells. Some single miRNAs or, more probably, their sets hold the promise for their use as biomarkers of atopic diseases. They are also promising target of future therapies.

Background. Gaining asthma control is still a challenge in a large number of patients. It could be facilitated by using biomarkers indicating the grade of inflammation and correlating with clinical picture. Chitinases and chitinase-like proteins play a role in Th2-type inflammation. Thus, they may be useful in diagnosing and monitoring of asthma. Objectives. The aim of the study was to investigate the relevance of YKL-40 as a good biomarker of asthma, its control, and severity. Methods. Level of YKL-40 was determined by means of immunoassay in sera of 59 asthmatics (39 women, 20 men, aged 23–76 years) and 29 healthy controls (18 women, 11 men, aged 20–80 years). Asthma severity and control were assessed according to GINA guidelines. Differences between groups were compared with the use of Mann–Whitney’s U-test. Correlations between variables were assessed with Pearson’s test. Results. Symptoms of asthma were found to be controlled in 12 (20%), partly controlled in 17 (29%), and uncontrolled in 30 (51%) patients. YKL-40 levels were significantly higher, on average, in asthmatics compared to control group (median levels: 125.3 U and 84.1 U, respectively, p < .001). YKL-40 correlated with the number of blood eosinophils (r = 0.376, p = 0.05). However, no relations have been found between YKL-40 level and asthma severity, control, or total serum IgE (r = −0.05, p = .05). Conclusion. YKL-40 seems to be a good marker of asthma. However, its level may not correlate with clinical outcome.

Purpose of review: MicroRNAs (miRNAs) are small noncoding RNA molecules that are considered one of the fundamental regulatory mechanisms of gene expression. They are involved in many biologic processes, such as signal transduction, cell proliferation and differentiation, apoptosis and stress responses. The purpose of this review is to present recent knowledge about the role of miRNAs in asthma and outline possible applications of miRNAs. Recent findings: A core set of miRNAs involved in asthma includes downregulated let-7 family, miR-193b, miR-375 as well as upregulated miR-21, miR-223, miR-146a, miR-142-5p, miR-142-3p, miR-146b and miR-155. Recently it has been shown that most of the involved miRNAs increase secretion of Th2 cytokines, decrease secretion of Th1 cytokines, promote differentiation of T cells towards Th2 or play a role in hyperplasia and hypertrophy of bronchial smooth muscle cells. The profiles of miRNAs correlate with clinical characteristics, including lung function, phenotype and severity of asthma. Summary: Recent publications confirmed crucial regulatory role of miRNAs in the pathomechanism of asthma. Some single miRNAs or their sets hold the promise for their use as asthma biomarkers facilitating diagnosis or prediction of treatment outcomes. They are also possible target of future therapies. The studies in this field are lacking though.

YKL-40 is a chitinase-like protein found to correlate with asthma as well as numerous infectious and autoimmune diseases or cancer. The aim of the present study was to investigate the role of YKL-40 as a possible marker of asthma and its associations with factors differentiating phenotypes of asthma.

The influence of respiratory infections on asthma has not been fully understood. Acute viral and bacterial infections often lead to exacerbations. Less is known about the role of chronic infections, particularly with atypical pathogens. The aim of this study was to evaluate the impact of Chlamydophila pneumoniae and Mycoplasma pneumoniae infections on the control and severity of asthma. Spirometry, skin-prick tests as well as measurement of immunoglobulin G (IgG), IgM, and IgA against C. pneumoniae and M. pneumoniae (ELISA) were performed in 95 patients with persistent asthma and 58 healthy controls. Additionally, in the selected group of asthmatic patients, presence of C. pneumoniae and M. pneumoniae genetic material was tested in induced sputum (polymerase chain reaction [PCR]). IgA against C. pneumoniae was found in 42 (44.2%) asthmatic patients and 17 (29.3%) controls (p < 0.05). It was found more often in the group with uncontrolled asthma (p = 0.001) as well as in nonatopic asthmatic patients (p < 0.05). IgG was detected in 58 asthmatic patients (61%) and 21 (36.2%) controls, more often in cases of uncontrolled (p < 0.05) and nonatopic asthma patients (p < 0.05). Such correlations were not found in relation to M. pneumoniae infections. C. pneumoniae was detected by means of PCR in respiratory secretions of eight asthmatic patients (40%), and M. pneumoniae was detected in two asthmatic patients (10%). In conclusion, C. pneumoniae infections are more frequent in asthmatic patients compared with healthy individuals and in nonatopic asthmatic patients compared to atopic patients. Chronic infection is associated with poor control of asthma.

Asthma is a heterogeneous chronic disorder of the airways, with inflammation and bronchial hyperresponsiveness as its major underlying phenomena. Asthmatics vary in terms of inflammation pattern, concomitant pathologies, and factors aggravating the course of the disease. As a result, there is a need for sensitive and specific biomarkers that could facilitate diagnosing asthma as well as phenotyping in everyday practice. Chitinases and chitinase-like proteins (CLPs) seem promising in this field. Chitinases are evolutionarily conserved hydrolases that degrade chitin. In contrast, CLPs bind chitin but do not have degrading activity. Mammalian chitinases and CLPs are produced by neutrophils, monocytes, and macrophages in response to parasitic or fungal infections. Recently, several questions have been raised about their role in chronic airway inflammation. Several studies demonstrated that overexpression of CLP YKL-40 was associated with asthma. Moreover, it correlated with exacerbation rate, therapy resistance, poor control of symptoms, and, inversely, with FEV₁. YKL-40 facilitated allergen sensitization and IgE production. Its concentration was elevated in bronchoalveolar lavage fluid after an allergen challenge. It was also found to promote the proliferation of bronchial smooth muscle cells and correlate with subepithelial membrane thickness. Thus, it may be involved in bronchial remodeling. Associations between YKL-40 and particular asthma phenotypes remain unclear. Some studies showed that YKL-40 correlates with blood eosinophilia and FeNO, suggesting a role in T2-high inflammation. Quite the opposite, cluster analyses revealed the highest upregulation in severe neutrophilic asthma and obesity-associated asthma. The main limitation in the practical application of YKL-40 as a biomarker is its low specificity. High serum levels of YKL-40 were also found in COPD and several malignancies, in addition to infectious and autoimmune diseases. To conclude, the level of YKL-40 correlates with asthma and some clinical features in the whole asthmatic population. The highest levels are found in neutrophilic and obesity-related phenotypes. However, due to its low specificity, the practical application of YKL-40 remains uncertain but could be useful in phenotyping, especially when combined with other biomarkers.