Phagocytosis by alveolar macrophages

It is believed that the lung infection results from impaired mucus clearance followed by colonization of bacteria in the mucus. The bacteria elaborate a number of toxins, polysaccharides, and enzymes including proteases, elastases, and exotoxin A, which may stimulate the production of additional mucus and further contribute to airway obstruction (Sam et al., 1980 Adler et al., 1983). Pseudomonas aeruginosa and Staphylococcus aureus are the most commonly found bacteria in the lungs of patients with CF, but Klebsiella, Esherichia coli, streptococci, and Haemophilus influenza can also be found. Of particular interest is the observation that mucoid strains of infectious bacteria, which are more pathogenic than nonmucoid strains, are most commonly found in patients with CF (Reynolds et al., 1975, 1976). The mucoid strains are also more resistant to phagocytosis by alveolar macrophages and are impermeable to antibiotics because of their mucoid coats. Thus treatment of pulmonary infections in patients with CF can be unusually difRcult. 

O Neill SJ, Lesperance E, Klass DJ. Human lung lavage surfactant enhances staphylococcal phagocytosis by alveolar macrophages. Am Rev Respir Dis 1984 130 1177-1179. 

FI G U RE 10.2 Schematic representation of alveolar cells and possible mechanism of transport of molecules from the alveolar space into the circulation. Particles will release molecules of interest (gray circles) into the mucus in which the particle is embedded. The molecule can either be lost in the mucus, taken up by alveolar macrophages by phagocytosis or diffusion, taken up by alveolar epithelial cells by passive or active transport, or bypass the alveolar cells via paracellular transport depending upon the properties of the drug. Once a molecule has reached the extracellular space, the same mechanisms are possible for transport from the extracellular space into the blood. Molecules in the extracellular space may also reach to circulation via the lymph. 

Evora C, Soriano I, Rogers RA, et al. Relating the phagocytosis of microparticles by alveolar macrophages to surface chemistry the effect of 1,2-dipalmitoylphosphatidylcholine. J Control Release 1998 51(2-3) 143-152. 

Hodge S,Hodge G, Brozyna S, et al. (2006) Azithromycin increases phagocytosis of apoptotic bronchial epithelial cells by alveolar macrophages. Eur Respir J 28 486-495... 

King TE, Savici D, Campbell PA. Phagocytosis and killing of Listeria monocytogenes by alveolar macrophages smokers versus nonsmokers. J Infect Dis 1988 158 1309-1316. 

Taya A, Carmack DB, Muggenburg BA, et al. 1992. An interspecies comparison of the phagocytosis and dissolution of 241Am02 particles by rat, dog and monkey alveolar macrophages in vitro. Int J Radiat Biol 62(l) 89-95. 

Renwick, L. C., Donaldson, K., and Clouter, A. Impairment of alveolar macrophage phagocytosis by ultrafine particles. Toxicol. Appl. Pharmacol. 172 119-127, 2001. 

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