Objective: to study the change of airway inflammation induced by Th1/Tc1 and the expression of CD4(+)CD25(+) regulatory T cells (Treg) in smoking cessation rats.
Methods: fifty healthy male Wistar rats were randomly divided into five groups: 12-week normal control (group A, n = 10), 24-week normal control (group B, n = 10), 12-week smoke exposure (group C, n = 10), 24-week smoke exposure (group D, n = 10) and smoking cessation (group E, n = 10). Groups C, D and E were exposed to cigarettes for 12 weeks. At Week 12, groups A and C were sacrificed. Group D continued smoke exposure and group E had smoking cessation for 12 weeks. At Week 24, groups B, D and E were sacrificed. Pathomorphological changes of small airway were analyzed. The cells in BALF (bronchoalveolar lavage fluid) were collected and analyzed by absolute and differential cell counts. Enzyme linked immunosorbent assay (ELISA) was used to detect the levels of IFN-γ, IL-4, IL-8 and TNF-α. And flow cytometry was employed to determine the Foxp3 + Treg cell populations and reverse transcription-polymerase chain reaction (RT-PCR) to assay the mRNA expression for Foxp3.
Results: (1) compared with groups A and B, the airway inflammation score of groups C, D and E increased significantly (all P < 0.01). Compared with group C, the airway inflammation score of groups D and E both increased (all P < 0.01), especially group D; (2) compared with groups A and B, the levels of IFN-γ, TNF-α and IL-8 in groups C, D and E increased (all P < 0.01) while those of IL-4 decreased. The levels of IFN-γ, TNF-α and IL-8 showed no difference between groups C and E. The levels of IFN-γ, TNF-α and IL-8 were higher in group D than those in groups C and E; (3) the ratio of Foxp3 + Treg cells in BALF was higher in group C (7.4% ± 0.8%), group D (7.8% ± 1.7%) and group E (7.0% ± 1.4%) than group A (4.8% ± 1.2%) and group B (4.7% ± 1.2%) (all P < 0.01). There were no differences in the ratio of Foxp3 + Treg cells among groups C, D and E (all P < 0.05); (4) there was an elevated expression of Foxp3 mRNA in group C (0.22 ± 0.02), group D (0.23 ± 0.03), group E (0.20 ± 0.04) versus group A (0.13 ± 0.01) and group B (0.11 ± 0.02) (all P < 0.01). But there was no difference in the expression of Foxp3 mRNA among groups C, D and E (all P > 0.05).
Conclusions: airway inflammation induced by Th1/Tc1 and an elevated expression of Treg cells in BALF are found in smoke exposure rats. Upon smoking cessation, the above-mentioned airway inflammation still persists and the expression of Treg cells in BALF shows no decrease. It suggests that an immune imbalance may be involved in the progression of Th1/Tc1-induced airway inflammation upon smoking cessation.