The role of interleukin-6 in pulmonary and systemic manifestations in a murine model of chronic obstructive pulmonary disease

Chronic obstructive pulmonary disease (COPD) is characterized by pulmonary and extrapulmonary manifestations including systemic inflammation and weight loss. Increased levels of interleukin-6 (IL-6) have been demonstrated in sputum and serum of COPD patients. Therefore, the authors investigated the in vivo role of IL-6 in a murine model of COPD. Wild-type (WT) and IL-6 knockout (KO) mice were exposed subacutely (4 weeks) and chronically (24 weeks) to air or cigarette smoke (CS). Subacute and chronic CS exposure significantly increased pulmonary IL-6 mRNA expression in lung tissue and IL-6 protein levels in bronchoalveolar lavage fluid of WT mice. However, CS-induced accumulation of inflammatory cells at both time points and lymphoid aggregate formation upon chronic CS exposure were independent of IL-6. Chonic CS exposure was associated with a significant failure to gain weight in both WT mice and IL-6 KO mice. Remarkably, air-exposed IL-6 KO mice have lower body weight, serum leptin levels, and adipose tissue mass compared to air-exposed WT mice. In conclusion, IL-6 is of minor importance in CS-induced pulmonary and systemic manifestations in mice, but this study confirms the role for IL-6 as regulator of body weight and body composition.