Objective: To investigate if CpG-oligodeoxynucleotides (CpG-ODN) intervention has inhibitory effects on the development of airway remodeling in an ovalbumin (OVA)-sensitized mouse model of chronic asthma.
Methods: Forty female C57BL/6 mice were randomly divided into four groups (n = 10): (1) Group A (chronic asthma model): mice were sensitized by intraperitoneal injection of OVA (10 microg) precipitated with aluminium hydroxide (100 microg) on days 1 and 14. From day 21, the mice were challenged by nebulized 2.5% OVA solution (30 min/d, three times a week for 8 weeks). (2) Group B (CpG-ODN intervention group): mice were sensitized and challenged as above, and were given 60 microg CpG-ODN by intraperitoneal injection for once every two weeks. (3) Group C (GpG-ODN control): Mice were given GpC-ODN instead of CpG motifs, other treatments same as Group B. (4) Group D (saline control): mice were sensitized and challenged by saline. All mice were killed 24 h after the final OVA challenge. Blood was obtained for eosinophil counts and measurement of serum IgE by enzyme-linked immunoabsorbent assay (ELISA). Bronchoalveolar lavage fluid (BALF) was collected for total and differential counts. The concentration of interleukin-13 (IL-13) and transforming growth factor-beta1 (TGF-beta(1)) in BALF was measured by ELISA. The left lung was isolated for pathological examination. Lung sections were stained with hematoxylin and eosin (HE), and Masson's trichrome. Other sections were prepared for immunohistochemistry using monoclonal antibodies against alpha-smooth muscle actin (alpha-SMA) and TGF-beta(1).
Results: The eosinophil count [(89 +/- 10) x 10(4)/ml], serum IgE [(279 +/- 53) ng/ml], BALF eosinophils [(6.30 +/- 1.30) x 10(5)/ml] and the concentrations of BALF IL-13 [(4 015 +/- 361) pg/ml] and TGF-beta(1) [(356 +/- 64) pg/ml] in the OVA-sensitized mice (Group A) showed significant difference as compared with those in the NS control group (Group D, t values are 24.0, 15.7, 14.7, 18.4, 12.0 and 18.9 respectively, all P < 0.01). In Group A, the percentages of positive staining area in Masson's trichrome, alpha-SMA staining and TGF-beta(1) staining were (29.7 +/- 4.2)%, (45 +/- 7)% and (34 +/- 4)% respectively. These percentages were significantly different from those in the NS control group (Group D, t values are 18.0, 15.6 and 17.9 respectively, all P < 0.01). In mice treated with CpG-ODN (Group B), the percentages of positive staining area in Masson's trichrome, alpha-SMA staining and TGF-beta(1) staining were (13.8 +/- 3.2)%, (24.7 +/- 3.1)%, (18 +/- 4)% respectively, which were significantly different from those in Group A (t values are 9.5, 8.9 and 9.8 respectively, all P < 0.05).
Conclusions: This study demonstrated that CpG-ODN could prevent Th2 responses, eosinophilic inflammation and the development of airway remodeling. Its inhibitory effect on airway remodeling might, in part, be due to inhibition of the expression of cytokines such as TGF-beta(1) and IL-13.