Am. J. Respir. Cell Mol. Biol.,
Volume 24, Number 5, May, 2001 640-646
Lipopolysaccharide Inhibits the Late-Phase Response to Allergen by
Altering Nitric Oxide Synthase Activity and Interleukin-10
Meri K.
Tuli
,
Darryl A.
Knight,
Patrick G.
Holt,
and
Peter D.
Sly
Divisions of Clinical Sciences and Cell Biology, Institute for Child Health Research, Center for Child Health Research; and Department of
Medicine, University of Western Australia, Perth, Australia
We have previously shown that exposure of sensitized animals
to lipopolysaccharide (LPS) 18 h after ovalbumin (OVA) challenge inhibits late-airway response (LAR). Using relatively selective nitric oxide synthase (NOS) inhibitors we have shown
that LPS upregulates inducible NOS (iNOS) and downregulates
constitutive NOS (cNOS) activity. In this study we set out to
quantitate NOS isoenzyme activity in lung homogenates and
to measure ex vivo interleukin (IL)-10 in tracheal explants of
naive or sensitized and OVA-challenged rats exposed to LPS.
iNOS activity was increased and cNOS activity reduced 6 h after LPS exposure in naive animals (n = 6, P < 0.001) and at 18 (n = 5, P < 0.001) or 24 (n = 5, P < 0.001) h after OVA challenge in sensitized animals. LPS exposure 18 h after OVA challenge in sensitized animals reversed OVA-induced changes in
NOS isoenzyme activities (n = 5, P < 0.001). In naive animals
IL-10 was increased 1 h after LPS exposure (n = 5, P < 0.001),
peaked at 3 h (n = 9, P < 0.001), and remained elevated above
baseline at 18 h (n = 11, P < 0.05). In sensitized animals, IL-10
was not increased until 18 h after OVA challenge (n = 11, P < 0.001). Due to the rapid IL-10 increase in naive animals the released IL-10 is likely to be preformed; however, in sensitized animals the results are consistent with de novo production of IL-10. In the sensitized and OVA-challenged group, exposure
to LPS 18 h after OVA produced a 3-fold increase in IL-10 at 3 h after LPS exposure (n = 5, P < 0.001). The time course and kinetics of IL-10 release in those animals was similar to that seen
in naive rats. These results support our previous conclusions on the basis of in vivo studies using isoenzyme inhibitors and have shown LPS to be able to reverse OVA-induced changes in NOS
isoenzyme activities during an established LAR. LPS-induced
release of IL-10 is thought to play an important immunomodulatory role in this model.
Abbreviations: bronchoalveolar lavage fluid, BALF; constitutive NOS,
cNOS; hyperresponsiveness, HR; immunoglobulin, Ig; interleukin, IL; inducible NOS, iNOS; late-phase response, LPR; lipopolysaccharide, LPS;
methacholine, MCh; microvascular leakage, MVL; nitric oxide, NO; NO
synthase, NOS; ovalbumin, OVA; phosphate-buffered saline, PBS.
