Morphological aspects of particle uptake by lung phagocytes

Abstract

Macrophages residing on the inner epithelial surfaces of airways and alveoli are the only lung phagocytes exposed directly to the environment. Their phagocytic and microbicidal activities are essential for maintaining this organ in a clean and sterile state. The morphology of these phagocytes can be investigated in situ only after implementing special techniques, which involve intravascular triple-perfusion of aqueous fixatives or instillation of nonpolar ones. Such studies have revealed the engulfment of particles by these cells to be rapid, the process being essentially complete within a day. Particles are entrapped within phagosomes and the host cells eventually transported out of the lungs by mucociliary action, macrophages with higher loads being more rapidly eliminated than those with lower ones. Very small particles or those persisting on the epithelial surfaces may be taken up by the eponymous cells. Translocation of particles into the underlying connective tissue and their subsequent phagocytosis by interstitial macrophages prolongs their retention time in the lungs. The still poorly studied pleural macrophages might be involved in cell-mediated immune responses within the pleural space. Intravascular pulmonary macrophages figure largely in the phagocytosis of circulating particles. The role played by dendritic cells in particle uptake by the lungs is not well understood. Airway and alveolar macrophages are the primary phagocytes of the lung. In nonoverload situations and for particles >1 microm, a small proportion of those recruited suffices to remove material from the epithelial surface before other phagocytes, with an apparently greater immunological potential, gain access to it.

Activation of Pulmonary Dendritic Cells and Th2-Type Inflammatory Responses on Instillation of Engineered, Environmental Diesel Emission Source or Ambient Air Pollutant Particles in vivo

“…A known route of PM clearance from the lung involves endocytic and phagocytic mechanisms by macrophages [15,16,35,47] . Thus PM uptake by macrophages or presumably DC may lead to their activation and subsequent release of ␤ -glucuronidase in the lung.…”

“…Interdigitated throughout the respiratory epithelium are specialized macrophages and professional antigen-presenting DC subsets [15][16][17] . Airway inflammation in allergic asthma reflects an aberrant immune response against otherwise harmless inhaled allergens.…”

“…ragweed extract) instructs 'non-classic' DC maturation enabling them to stimulate a complex pattern of Th1-and Th2-associated responses [6,12,18,19] . The exact location of where DCs sample respirable antigen in the lung remains ill-defined [15,16] , although it is known that DC serve a key role in the immune pathology of allergic asthma [20][21][22] .…”

Nanotoxicity: emerging concerns regarding nanomaterial safety and occupational hard metal (WC-Co) nanoparticle exposure

“…22,26,102,103 Although the effects of WC-Co particles have been established in multiple cell lines of varying origin, most of these studies used mono-culture systems in their examination of WC-Co particle toxicity, which may not provide an accurate assessment of what happens during/after WC-Co exposure since the local environment of the lung is highly dynamic and contains more than a single cell type. In a recent study, 87 the inflammatory response toward nano-WC-Co particles in macrophages and the toxicity of WC-Co have been examined using a co-culture model of lung epithelial cells and macrophages to more closely represent the dynamic tissue environment of the lung.…”

Cellular Defences of the Lung: Comparative Perspectives

“…If they reach the alveolar surface, they are dealt with by the PSMs (e.g. Bowden, 1976;Goldstein and Bartlema, 1977;Geiser, 2002).…”