Other notable proteins previously described include apoptosis regulator Bcl-2 (an apoptosis suppressor downregulated in COPD resulting in emphysema progression) [59, 60], IL1RN (an inflammatory antagonist decreased in emphysema, contrary to our finding of a positive association) [61, 62], ROBO2 (a receptor downregulated and inversely associated with progression of COPD and involved in alveolar regeneration in a murine model of cigarette-smoke induced emphysema) [63, 64], and adiponectin (mediated inflammation in a murine model of cigarette smoke-induced emphysema) [65]. Here, ROBO2 is linked to chronic obstructive pulmonary disease.