CD9 and chronic obstructive pulmonary disease: In conclusion, based on previous studies suggesting that reduction in the levels of tetraspanin CD9/CD81 may be an underlying mechanism of COPD progression, we screened a drug library for agents that upregulate macrophage CD9/CD81, and found that statins decrease LPS-induced inflammation in mice by blockade of mevalonate pathway-dependent downregulation of CD9.