Macrophage activation in exacerbated COPD with and without community-acquired pneumonia

In large series of nonresponding community-acquired pneumonia (CAP) patients, chronic obstructive pulmonary disease (COPD) was observed to be a protective factor for nonresponse to initial antibiotics. This intriguing fact may be linked to changes in the phenotype of inflammatory cells and, in particular, to the induction of classical-M1 or alternative-M2 activation of macrophages, which result in different inflammatory profiles. We evaluated the effect of sputum obtained from patients with acute exacerbation of COPD (AECOPD), CAP and COPD+CAP on the phenotypic changes in macrophages. Human THP1 cells differentiated to macrophages were incubated with sputum from patients with AECOPD, CAP or COPD+CAP, and expression of tumour necrosis factor-alpha, interleukin-6, mannose receptor and arginase was measured to evaluate the phenotype acquired by macrophages. We found that sputum from CAP patients induced the M1 phenotype and that from AECOPD patients induced an M2-like phenotype. Sputum from CAP+COPD patients did not present a clear M1 or M2 phenotype. These results indicate that the microenvironment in the lung modulates the activation of macrophages, resulting in different phenotypes in AECOPD, CAP and COPD+CAP patients. This different type of activation induces different inflammatory responses and may be involved in the different outcome observed when COPD and CAP present simultaneously.