Background Smoking causes frequent asthma attacks,leading to a rapid decline in lung function in patients with asthma,and it can also reduce the therapeutic effect of glucocorticeids in patients with asthma.Therefore,the present study aimed to investigate the effect of cigarette smoke on the expression of myeloid differentiation factor 88 (MyD88) in marrow dendritic cells (DCs) in asthmatic rats,and to explore the molecular mechanism of cigarette smoke exposure on asthma by DCs.Methods Forty Wistar rats were randomly divided into the following groups:control,smoke exposure,asthma,and asthma combined with smoke exposure.The animal model was established,and then rat bone marrow-derived DCs were collected.Additionally,rat spleen lymphocytes and bone marrow-derived DCs were cultured together for mixed lymphocyte responses.Interferon (IFN)-gamma and interleukin (IL)-4,IL-10,and IL-12 expressions were determined by enzyme-linked immunosorbent assay (ELISA).MyD88 expression was determined by West blotting.The proliferation of lymphocytes was examined with methyl thiazolyl tetrazolium (MTT) colorimetric assay.Results MyD88 expression was decreased in the asthma combined with smoke exposure group compared to the asthma group (P＜0.01),and IL-10 and IL-12 expressions were decreased in the asthma combined with smoke exposure group compared to control group (P＜0.01).In addition,DCs stimulating activity on allogeneic lymphocytes were significantly decreased in the smoke exposure combined with asthma group compared to the control and asthma groups (P＜0.01).After allogeneic mixed lymphocyte responses,IL-4 expression was increased and IFN-gamma was decreased in the asthma group and the asthma combined with smoke exposure group compared to control group (P＜0.01).IL-4expression was increased and IFN-gamma was decreased in the asthma combined with smoke exposure group compared to the asthma group (P＜0.01).The study also showed that MyD88 expression was positively correlated with IL-12 and IFN-gamma expressions and the activity of lymphocytes (P＜0.01),and negatively correlated with IL-4expression (P＜0.01).Conclusions Smoking aggravates asthma by weankening immunological mechanism.MyD88-dependent pathways may play a role in the immunological balance and activation of lymphocytes.