Surfactant protein a stimulates the phagocytosis of specific
pulmonary pathogens by alveolar macrophages.
Tino, Michael James, and Jo Rae Wright.
Department of Cell Biology, Duke University Medical Center, Durham
NC 27710
APStracts 2:0218L, 1995.
Surfactant protein A (SP-A) regulates alveolar macrophage function and
has been implicated in the mediation of pulmonary host defense. Our
goals were to characterize the interaction of SP-A with various
pulmonary pathogens, to investigate the mechanism of SP-A mediated
phagocytosis using an assay that distinguishes bound from
internalized bacteria by quenching the fluorescence of extracellular
bacteria, and to examine further the interactions of SP A and the
structurally homologous protein C1q with alveolar macrophages and
peripheral blood monocytes. We found that SP-A binds to and increases
the phagocytosis of Haemophilus influenzae, Streptococcus pneumoniae,
and Group A Streptococcus; SP-A aggregates only H. influenzae. SP-A
neither binds to, aggregates, nor stimulates the phagocytosis of
Pseudomonas aeruginosa. We have also found that bronchoalveolar
lavage stimulates phagocytosis and that this stimulation is reduced
by an anti-SP A antibody. While the enhancement of phagocytosis by
SP-A is inhibited in blood monocytes adhered to C1q-coated surfaces,
which presumably clusters the C1q receptor on the basal surface of
the cell, alveolar macrophages on C1q-coated slides show no
significant change in their response to SP-A. In summary, SP-A
stimulates the phagocytosis by alveolar macrophages of specific
pulmonary pathogens to which it binds, but aggregation is not
required for the effect. Additionally, the role of the C1q receptor
in the response to SP-A may differ between monocytes and alveolar
macrophages.
Received 17 May 1995; accepted in final form 15 November 1995.
APS Manuscript Number L153-5.
Article publication pending Am. J. Physiol. (Lung Cell. Mol.
Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 8 December 95