Differential polarization of alveolar macrophages and bone marrow-derived monocytes following chemically and pathogen-induced chronic lung inflammation.

Alveolar macrophages and BDMCs undergo sequential biochemical changes during the chronic inflammatory response to chemically induced lung carcinogenesis in mice. Herein, we examine two chronic lung inflammation models-repeated exposure to BHT and infection with Mycobacterium tuberculosis-to establish whether similar macrophage phenotype changes occur in non-neoplastic pulmonary disease. Exposure to BHT or M. tuberculosis results in pulmonary inflammation characterized by an influx of macrophages, followed by systemic effects on the BM and other organs. In both models, pulmonary IFN-gamma and IL-4 production coincided with altered polarization of alveolar macrophages. Soon after BHT administration or M. tuberculosis infection, IFN-gamma content in BALF increased, and BAL macrophages became classically (M1) polarized, as characterized by increased expression of iNOS. As inflammation progressed in both models, the amount of BALF IFN-gamma content and BAL macrophage iNOS expression decreased, and BALF IL-4 content and macrophage arginase I expression rose, indicating alternative/M2 polarization. Macrophages present in M. tuberculosis-induced granulomas remained M1-polarized, implying that these two pulmonary macrophage populations, alveolar and granuloma-associated, are exposed to different activating cytokines. BDMCs from BHT-treated mice displayed polarization profiles similar to alveolar macrophages, but BDMCs in M. tuberculosis-infected mice did not become polarized. Thus, only alveolar macrophages in these two models of chronic lung disease exhibit a similar progression of polarization changes; polarization of BDMCs was specific to BHT-induced pulmonary inflammation, and polarization of granuloma macrophages was specific to the M. tuberculosis infection.