Background Asthma is considered to be a chronic inflammatory disorder of the airways. Probiotics are living microorganisms that are found in the human gut and have protective effects against a wide range of diseases such as allergies. The aim of this study was to investigate the improvement of clinical asthma symptoms and changes in the expression pattern of selective microRNAs in patients with asthma and the changes in IL-4 and IFN-γ plasma levels after receiving probiotics. Materials and methods The present study was a randomized, double-blind, placebo-controlled trial that enrolled 40 asthmatic patients. They were treated with probiotics or placebo: 1 capsule/day for 8 weeks. Pulmonary function tests, IL-4 and IFN-γ levels, and expression of microRNAs were assessed at baseline and after treatment. Results The results showed that the expression of miR-16, miR146-a and IL-4 levels in patients with asthma after receiving probiotic supplementation was significantly reduced and miR-133b expression was increased. In addition, pulmonary function tests showed a significant improvement in Forced Expiratory Volume in 1 s and Forced Vital Capacity after receiving probiotics. Conclusion In our study, 8-week treatment with probiotic supplementation led to reduced Th2 cells-associated IL-4 and improved Forced Expiratory Volume and Forced Vital Capacity. It appears probiotics can be used in addition to common asthma treatments.

<b><i>Introduction:</i></b> The favorable effects of probiotics have been demonstrated in allergic disorders. However, the underlying immunological mechanisms are poorly understood. In the present study, we investigated the improvement of clinical symptoms and immunological balance after receiving probiotics in patients with asthma. <b><i>Methods:</i></b> The present study was a randomized, double-blind, placebo-controlled trial in which 40 patients with asthma were enrolled. They were treated with probiotics or placebo: 1 capsule/day for 8 weeks. Pulmonary function test, percentage of CD4⁺ CD25⁺ FoxP3⁺ Tregs, and gene expression of T-bet, GATA-3, RORγt, and Foxp3 in PBMCs were assessed at baseline and after treatment. <b><i>Results:</i></b> Our results showed a significant increase in the expression of FoxP3 and CD4⁺ CD25⁺ FoxP3⁺ Tregs population, while RORγt and GATA3 expression were reduced. In addition, pulmonary function tests showed a significant improvement in forced expiratory volume and forced vital capacity after receiving probiotics. <b><i>Discussion/Conclusion:</i></b> Our findings demonstrate that 8-week treatment with probiotic supplementation can control T-helper 2-predominant and Th17 pro-inflammatory responses and improve forced vital and forced expiratory volume in asthmatic patients. It seems probiotics can be used besides common treatments for patients with asthma.

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