Am. J. Respir. Cell Mol. Biol., Vol 14, No. 2, 02 1996, 155-160.
Alveolar macrophage uptake of the environmental particulate titanium dioxide: role of surfactant components
B Stringer and L Kobzik
Physiology Program, Harvard School of Public Health, Boston, Massachusetts 02115, USA.
Pulmonary surfactant components can modulate uptake of microorganisms and
viruses by alveolar macrophages (AMs), but little is known about their role
in the uptake and clearance of inert environmental particulates. We tested
the hypotheses that surfactant components [e.g., surfactant protein A (SpA)
and the artificial bovine surfactant Survanta] modulate phagocytosis of
inert environmental particulates by acting as particle opsonins, or by
direct activation of AMs. AM uptake of a model inert particulate [titanium
dioxide (TiO2)] was measured using flow cytometry to quantitate increased
right angle scatter caused by particle uptake (e.g., fold increase in right
angle scatter versus control: 2.6 +/- 0.3; and 5.0 +/- 0.2 for AMs plus
TiO2, 20 and 80 micrograms/ml TiO2, respectively). Opsonization of TiO2
with surfactant components resulted in a modest increase in AM uptake
compared with that of unopsonized TiO2 [e.g., fold increase, uptake of TiO2
(50 micrograms/ml), opsonized with SpA, Survanta, and rat immunoglobulin G,
respectively: 1.6 +/- 0.1; 1.3 +/- 0.01; 1.5 + 0.02, n = 3-4]. Uptake of
inert latex beads was similarly enhanced after opsonizing with SpA and
Survanta (beads per cell: unopsonized, 3.2 +/- 0.40; SpA, 5.0 +/- 0.55;
Survanta, 6.0 +/- 0.12; n = 3-6). Pretreating AMs with surfactant
components and measuring the subsequent uptake of unopsonized TiO2 resulted
in approximately the same magnitude of enhancement. The data indicate that
surfactant components can increase AM phagocytosis of environmental
particulates in vitro, but only slightly relative to the already avid AM
uptake of unopsonized particles.
