Figure 1. Passive-smoking rats showed higher serum β₂-AAb levels than control rats before alveolar airspaces became enlarged.

(A) Levels of β₂-AAb in serum samples of CS-exposed rats and control rats were assessed at different time points. SE-ELISAs were performed after rats were exposed to clean air or cigarette smoke for 4, 8, 12, or 16 weeks. (B) Statistical analyses of mean linear intercept (MLI) measurements of lung sections after rats were exposed to clean air or cigarette smoke for 8 or 16 weeks. (C) Sections of lungs from a control rat and from a CS-exposed rat sacrificed at the end of the 8^th or 16^th week. Haematoxylin-eosin staining, scale bar = 200 μm. (D) and (E) Lower and higher groups refer to CS-exposed rats with relatively lower and higher serum β₂-AAb levels, respectively, and results of the statistical analysis of serum β₂-AAb levels and MLI values of the two groups were shown in panel (D) and (E) respectively. *p < 0.05, **p < 0.01, ***p < 0.001; Control group vs Smoke group or Lower group vs Higher group (n = 18 for the Control group and Smoke group at the 4^th or 8^th week in panel A, n = 12 for the Control group and Smoke group at the 12 ^th or 16^th week in panel A; n = 6 for the Control group and Smoke group at the 8^th week in panel B, n = 12 for the Control group and Smoke group at the 16^th week in panel B; n = 6 for the Lower group and Higher group at the 16^th week in panels D and E).