Immunosuppressive effects of honokiol in a mouse model of particulate matter 2.5-induced asthma

Abstract

Objective To investigate the anti-inflammatory and immunosuppressive effects of honokiol in a mouse model of particulate matter (PM) 2.5-induced asthma. Methods Female SPF BALB/c mice were randomly divided into five groups: normal saline group (group A), ovalbumin (OVA)-sensitized group (group B), PM2.5-exposed+ OVA-sensitized group (group C), dexamethasone-treated group (group D) and honokiol-treated group (group E). All mice except those in group A were sensitized and challenged with OVA, and the mice in groups C, D and E were exposed to PM2.5 every two days since the first challenge. Samples of lung sections were stained with hematoxylin and eosin (HE) to observe inflammatory infiltration. Bronchoalveolar lavage fluid (BALF) and PBMCs were collected from each mouse. Expression of RORγt and Foxp3 at mRNA level was detected by quantitative real-time PCR. Flow cytometry analysis was performed to measure the percentages of Th17 and Treg cells. ELISA was performed to measure the levels of IFN-γ, IL-10 and IL-17 in the supernatants of cell culture. Results Compared with group B, group C showed an enhanced expression of RORγt at mRNA level, increased IL-17 level and up-regulated percentage of Th17 cells (all P<0.05), but a suppressed expression of Foxp3 at mRNA level, decreased IL-10 level and down-regulated percentage of Th17 cells (all P<0.05). No significant difference in the percentage of Th1 cells or in the expression of Th1-related cytokines was observed. The expression of RORγt at mRNA level, IL-17 level and the percentage of Th17 cells were decreased in PM2.5-exposed mice upon honokiol intervention (all P<0.05), while the expression of Foxp3 at mRNA level, IL-10 level and the percentage of Treg cells were increased after honokiol intervention (all P<0.05). Honokiol had similar efficacy to dexamethasone in the treatment of asthma. Conclusion Honokiol can alleviate airway inflammation in mice with PM2.5 exposure-induced asthma through regulating the percentages of Th17 and Treg cells. Key words: Asthma; Particulate matter; Th17 cell; Treg cell; Honokiol