Background:Fine particulate matter (PM2.5) exacerbates airway inflammation and hyperreactivity in patients with asthma,but the mechanism remains unclear.The aim of this study was to observe the effects of prolonged exposure to high concentrations of PM2.5 on the pathology and airway hyperresponsiveness (AHR) of BALB/c mice undergoing sensitization and challenge with ovalbumin (OVA) and to observe the effects of apoptosis and T-cell immunoglobulin and mucin domain 1 (TIM-l) in this process.Methods:Forty female BALB/c mice were divided into four groups:control group,OVA group,OVA/PM group,and PM group (n =10 in each group).Mice in the control group were exposed to filtered clean air.Mice in the OVA group were sensitized and challenged with OVA.Mice in the OVA/PM group were sensitized and challenged as in the OVA group and then exposed to PM2.5 for 4 h per day and 5 days per week for a total of 8 weeks using a nose-only PM2.5 online enrichment system in The Second Hospital of Hebei Medical University.Mice in the PM group were exposed to the PM2.5 online enrichment system only.AHR was detected.Bronchoalveolar lavage fluid (BALF) was collected for cell classification.The levels of interleukin-4 (IL-4),IL-5,and IL-33 in BALF were measured using enzyme-linked immunosorbent assay.Changes in histological structures were examined by light microscopy,and changes in ultramicrostructures were detected by electron microscopy.Apoptosis was determined by terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling (TUNEL) assay in the lung tissues.West blotting and immunohistochemistry were utilized to analyze the expression of Bcl-2,Bax,and TIM-1 in the lungs.Results:The results showed that AHR in the OVA/PM group was significantly more severe than that in the OVA and PM groups (P ＜ 0.05).AHR in the PM group was also considerably more severe than that in the control group (P ＜ 0.05).The BALF of OVA/PM group (28.00 ± 6.08 vs.12.33 ± 4.51,t =4.631,P =0.002) and PM group (29.00 ± 3.00 vs.12.33 ± 4.51,t =4.927,P =0.001) had more lymphocytes than the BALF of the control group.The number of neutrophils in the BALF of the OVA/PM group (6.67 ± 1.53 vs.3.33 ± 1.53,t =2.886,P =0.020) and PM group (6.67 ± 1.53 vs.3.33 ± 1.53,t =2.886,P =0.020) was much higher than those in the BALF of OVA group (P ＜ 0.05).TUNEL assays showed that the number of apoptotic cells in the OVA/PM group was significantly higher than that in the OVA group (Tunel immunohistochemical scores [IHS％],1.20 ± 0.18 vs.0.51 ± 0.03,t =8.094,P ＜ 0.001) and PM group (Tunel IHS％,1.20 ± 0.18 vs.0.51 ±-0.09,t =8.094,P ＜ 0.001),and that the number of apoptotic cells in the PM group was significantly higher than that in the control group (Tunel IHS％,0.51 ± 0.09 vs.0.26 ± 0.03,t =2.894,P =0.020).The concentrations of IL-4 (77.44 ± 11.19 vs.48.02 ± 10.02 pg/ml,t =4.595,P =0.002) and IL-5 (15.65 4± 1.19 vs.12.35 ± 0.95 pg/ml,t =3.806,P =0.005) and the Bax/Bcl-2 ratio (1.51 ± 0.18 vs.0.48 4± 0.10,t =9.654,P ＜ 0.001) and TIM-1/β-actin ratio (0.78 ± 0.11 vs.0.40 ± 0.06,t =6.818,P ＜ 0.001) in the OVA/PM group were increased compared to those in the OVA group.The concentrations of IL-4 (77.44 ± 11.19 vs.41.47 ± 3.40 pg/ml,t =5.617,P=0.001)and IL-5 (15.65 4 1.19 vs.10.99 ± 1.40 pg/ml,t =5.374,P =0.001)and the Bax/Bcl-2 ratio (1.51 ± 0.18 vs.0.97 ± 0.16,t =5.000,P =0.001) and TIM-1/β-actin ratio (0.78 ± 0.11 vs.0.31 ± 0.06,t =8.545,P ＜ 0.001) in the OVA/PM group were increased compared to those in the PM group.The concentration ofIL-4 (41.47-± 3.40 vs.25.46 ± 2.98 pg/ml,t =2.501,P =0.037) and the Bax/Bcl-2 ratio (0.97 ± 0.16 vs.0.18 ± 0.03,t =7.439,P ＜ 0.001) and TIM-1/β-actin ratio (0.31 ± 0.06 vs.0.02 ± 0.01,t =5.109,P =0.001) in the PM group were also higher than those in the control group.Conclusions:Exacerbated AHR associated with allergic asthma caused by PM2.5 is related to increased apoptosis and TIM-1 activation.These data might provide insights into therapeutic targets for the treatment of acute exacerbations of asthma induced by PM2.5.