Doy. Cheung et al., Role of pulmonary alveolar macrophages in defense of the lung against Pseudomonas aeruginosa, INFEC IMMUN, 68(8), 2000, pp. 4585-4592
Alveolar macrophages (AM) provide one of the first lines of defense against
microbial invasion in the lower airways, The role of AM in the clearance o
f Pseudomonas aerrcginosa in mice after intrapulmonary challenge was evalua
ted. AM were depleted by intranasal administration of liposome-encapsulated
dichloromethylene diphosphonate, At 24 h following the instillation of lip
osomes, a sublethal dose of P. aeruginosa was inoculated intranasally. Sple
en, liver, and lung tissue was then evaluated for viable bacteria and for h
istopathology, AM depletion of 78 to 88% did not affect the survival rate o
f infected mice or clearance of P. aeruginosa from the spleen, liver, or lu
ng, compared to the control group, but the mice's susceptibility to Klebsie
lla pneumoniae was greatly enhanced. The recruitment of neutrophils to the
lung was also not affected. Freshly explanted AM were not competent to phag
ocytose unopsonized P. aeruginosa but were able to phagocytose zymosan part
icles. Further studies were conducted to assess the in situ phagocytic acti
vities of AM, Three hours after the intranasal instillation of P. aeruginos
a or other particles, bronchoalveolar lavage was performed. AM phagocytosis
of zymosan particles and latex beads exceeded that of P. aeruginosa, Neutr
ophils were recruited to the lung in response to a high-dose bacterial chal
lenge. These results suggest that AM do not play an important role in defen
se of the lung against P. aeruginosa.