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Infection and Immunity, January 2005, p. 352-361, Vol. 73, No. 1
0019-9567/05/$08.00+0     doi:10.1128/IAI.73.1.352-361.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

Differential Roles of Toll-Like Receptors 2 and 4 in In Vitro Responses of Macrophages to Legionella pneumophila

First Department of Internal Medicine, Graduate School of Medicine, University of the Ryukyus, Okinawa,¹ Research Institute for Microbial Infectious Disease, Osaka University, Osaka, Japan²

Received 25 March 2004/ Returned for modification 24 May 2004/ Accepted 24 September 2004

The role of Toll-like receptors (TLRs) in innate immunity to Legionella pneumophila, a gram-negative facultative intracellular bacterium, was studied by using bone marrow-derived macrophages and dendritic cells from TLR2-deficient (TLR2^–/–), TLR4^–/–, and wild-type (WT) littermate (C57BL/6 x 129Sv) mice. Intracellular growth of L. pneumophila was enhanced within TLR2^–/– macrophages compared to WT and TLR4^–/– macrophages. There was no difference in the bacterial growth within dendritic cells from WT and TLR-deficient mice. Production of interleukin-12p40 (IL-12p40) and IL-10 after infection with L. pneumophila was attenuated in TLR2^–/– macrophages compared to WT and TLR4^–/– macrophages. Induction of IL-12p40, IL-10, and tumor necrosis factor alpha secretion from macrophages by the L. pneumophila dotO mutant, which cannot multiply within macrophages, and heat-killed bacteria, was similar to that caused by a viable virulent strain. There was no difference between the WT and its mutants in susceptibility to the cytopathic effect of bacteria. An L. pneumophila sonicated lysate induced IL-12p40 production by macrophages, but that of TLR2^–/– macrophages was significantly lower than those of WT and TLR4^–/– macrophages. Treatment of L. pneumophila sonicated lysate with proteinase K and heating did not abolish TLR2-dependent IL-12p40 production. Our results show that TLR2, but not TLR4, is involved in murine innate immunity against L. pneumophila, although other TLRs may also contribute to innate immunity against this organism.

Editor: F. C. Fang

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