Fig. 1.

Inhalation of PM into alveoli. The PM interacts with pulmonary surfactant in various ways depending on surface properties (surface charge, hydrophobicity, size, shape, etc.) of the particles. 1,2-dipalmitoyl-sn-glycero-3-phosphatidylcholine (DPPC) is used as the representative of lung surfactant. PM may embed into lung surfactant individually or in aggregates, with or without lipid wrapping. The defense mechanism of the surfactant can launch clearance to expel the impinging PM. PM can also penetrate lung surfactant to invade capillaries. The interaction of PM with bilayer vesicles would impede the metabolism of lung surfactant. Meanwhile, lipids may also transfer to the surface of PM to affect the behavior of PM in alveoli. This transfer also sequesters part of lung surfactant.