Fig. 2.

Mechanism showing HP development by increasing host susceptibility through air pollution exposure. a) Emission of industrial and traffic-related air pollution. Pollutants reach the alveolar spaces in the lungs and induce epigenetic changes in the lungs’ microenvironment, thereby influencing host susceptibility to disease development. b) The interaction between the causative antigen deposited in alveolar spaces and the circulating IgG antibody forms precipitating antigen-antibody immune complexes in interstitial spaces. Immune complexes trigger activation of both complement and pulmonary macrophages. Activated macrophages secrete the cytokines IL-1 and TNF-a that promote adhesion of leukocytes to activated endothelium. Complement activation enhances vascular permeability and attracts inflammatory cells. As a consequence of recruitment and activation, inflammatory cells release toxic mediators that promote acute lung injury, which eventually leads to HP development