Infection and Immunity, December 2000, p. 6567-6573, Vol. 68, No. 12
0019-9567/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
Department of Chemotherapy, Schering Plough Research Institute, Kenilworth, New Jersey,1 and DNAX Research Institute, Palo Alto, California2
Received 25 May 2000/Returned for modification 16 July 2000/Accepted 22 August 2000
The in vivo role of endogenous interleukin-18 (IL-18) in modulating
gamma interferon (IFN-
)-mediated resolution of replicative Legionella pneumophila lung infection was assessed using a
murine model of Legionnaires' disease. Intratracheal inoculation of
A/J mice with virulent bacteria (106 L. pneumophila organisms per mouse) resulted in induction of IL-18
protein in bronchoalveolar lavage fluid (BALF) and intrapulmonary expression of IL-18 mRNA. Real-time quantitative RT-PCR analysis of
infected lung tissue demonstrated that induction of IL-18 in BALF
preceded induction of IL-12 and IFN-
mRNAs in the lung. Blocking
intrapulmonary IL-18 activity by administration of a monoclonal
antibody (MAb) to the IL-18 receptor (anti-IL-18R MAb) prior to
L. pneumophila infection inhibited induction of
intrapulmonary IFN-
production but did not significantly alter
resolution of replicative L. pneumophila lung infection. In
contrast, blocking endogenous IL-12 activity by administration of
anti-IL-12 MAb) alone or in combination with anti-IL-18R MAb inhibited
induction of intrapulmonary IFN-
and resulted in enhanced
intrapulmonary growth of the bacteria within 5 days postinfection.
Taken together, these results demonstrate that IL-18 plays a key role
in modulating induction of IFN-
in the lung in response to L. pneumophila and that together with IL-12, IL-18 regulates
intrapulmonary growth of the bacteria.
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