Aims : COPD is a very heterogeneous disease. The classical paradigm, namely, that cigarette smoke-induced inflammation and proteinase-antiproteinase imbalance are the main players in the pathogenesis of COPD, has recently been called into question. The varying degree of susceptibility to COPD among individuals and the fact that susceptible ever-smokers continue to have progressive lung parenchymal disease indicate a much more complex immune response to the insulting agent.