Effect of CS smoke on active caspase 3 activation in rat lungs. (A) Representative pictures show the IHC staining of active caspase 3 at 3 days, 8 weeks and 6 months CS smoke-exposed rat lungs. Arrows represent cells positively stained for active caspase 3. (B) Graph representing positive cell counts in rat lungs. There was no difference in the number of positively stained cells between sham-exposed and CS-exposed animals after either 3 days, 8 weeks or 6 months of CS exposure in rat lungs (n = 6).