MicroRNA–21 as a novel biomarker in diagnosis and response to therapy in asthmatic children

•expression levels of miRNA-21 were higher in the asthmatic children.•IL12 p35 levels were significantly decreased in asthmatic patients.•serum miRNA-21 expression was correlated with serum IL12 p35 levels and FEV1.•miRNA-21 has differentiates ICS sensitive from ICS resistant. The underlying molecular mechanisms leading to asthma remain largely unclear. MicroRNAs (miRNAs) are short noncoding RNAs exert powerful effects on immunological function by tuning networks of target genes that orchestrate cell activity. However, the role of miRNAs, specifically microRNA-21 (miRNA- 21), in the regulation of allergic airway inflammation is not well defined. Our aim was to investigate the serum miRNA- 21 expression levels as potential biomarker in childhood asthma [with, without inhaled corticosteroid (ICS) therapy, and steroid resistant (SR)]; and their possible contributions in disease status, its molecular target interleukin-12 (IL-12) p35, and response to therapy. This study included 175 children; 95 were asthmatic patients subdivided into 3 groups [40 asthmatic children without ICS, 40 steroid sensitive (SS) asthma children and 15 steroid resistant (SR) asthma children] and 80 were healthy children as healthy controls. The miRNA-21 expressions levels were determined by quantitative real-time polymerase chain reaction (qRT-PCR) in all children. Serum IL-12p35 and total IgE levels were measured using enzyme-linked immunosorbent assay (ELISA). The expression levels of miRNA-21 were significantly higher in the asthmatic children than in control group (P