Legionella pneumophila is the cause of Legionnaires' disease, which is a form of potentially fatal pneumonia. To identify genes required for virulence of the bacterium, a library of 1,386 L. pneumophila signature tagged transposon mutants was studied for guinea pig virulence. The mutants were screened in pools of 96 each in a guinea pig model of L. pneumophila pneumonia. Sixteen unique mutant clones were determined to have attenuated virulence after being screened twice in the animal model. All 16 mutants failed to multiply in both lungs and spleens. Four of the sixteen had no apparent defect for intracellular multiplication in macrophages. Partial DNA sequences of the interrupted genes adjacent to the transposon insertions showed that six of them had mutations in five known L. pneumophila virulence genes: dotB, dotF͞icmG, dotO͞icmB, icmX, and proA. Three of the sequenced clones contained mutations in genes without known homology to other published bacterial genes, and seven clones appeared to be homologous to five different known bacterial genes but are still being characterized. With this methodology, we demonstrate the existence of L. pneumophila genes responsible for non-macrophage-related virulence. The discovery of L. pneumophila virulence genes indicates the utility of the signature tagged mutagenesis technique for pulmonary pathogens.

BackgroundLegionella pneumophila is the causative agent of human Legionnaire's disease. During infection, the bacterium invades macrophages and lung epithelial cells, and replicates intracellularly. However, little is known about its interaction with T cells. We investigated the ability of L. pneumophila to infect and stimulate the production of interleukin-8 (IL-8) in T cells. The objective of this study was to assess whether L. pneumophila interferes with the immune system by interacting and infecting T cells.ResultsWild-type L. pneumophila and flagellin-deficient Legionella, but not L. pneumophila lacking a functional type IV secretion system Dot/Icm, replicated in T cells. On the other hand, wild-type L. pneumophila and Dot/Icm-deficient Legionella, but not flagellin-deficient Legionella or heat-killed Legionella induced IL-8 expression. L. pneumophila activated an IL-8 promoter through the NF-κB and AP-1 binding regions. Wild-type L. pneumophila but not flagellin-deficient Legionella activated NF-κB, p38 mitogen-activated protein kinase (MAPK), Jun N-terminal kinase (JNK), and transforming growth factor β-associated kinase 1 (TAK1). Transfection of dominant negative mutants of IκBα, IκB kinase, NF-κB-inducing kinase, TAK1, MyD88, and p38 MAPK inhibited L. pneumophila-induced IL-8 activation. Inhibitors of NF-κB, p38 MAPK, and JNK blocked L. pneumophila-induced IL-8 expression. In addition, c-Jun, JunD, cyclic AMP response element binding protein, and activating transcription factor 1, which are substrates of p38 MAPK and JNK, bound to the AP-1 site of the IL-8 promoter.ConclusionsTaken together, L. pneumophila induced a flagellin-dependent activation of TAK1, p38 MAPK, and JNK, as well as NF-κB and AP-1, which resulted in IL-8 production in human T cells, presumably contributing to the immune response in Legionnaire's disease.

Osteopontin (OPN, also known as Eta-1), a noncollagenous matrix protein produced by macrophages and T lymphocytes, is expressed in granulomatous lesions caused by Mycobacterium tuberculosis infection. In the present study, we compared plasma concentrations of OPN in patients with active pulmonary tuberculosis with those of healthy control subjects and patients with sarcoidosis, another disease associated with granuloma formation. Plasma OPN levels were significantly higher in patients with tuberculosis (n = 48) than in control subjects (n = 34) and patients with sarcoidosis (n = 20). OPN levels correlated well with severity of pulmonary tuberculosis, as indicated by the size of lung lesions on chest X-ray films. Furthermore, chemotherapy resulted in a significant fall in plasma OPN levels. In patients with tuberculosis, plasma OPN concentrations correlated significantly with those of interleukin (IL)-12. In vitro experiments showed that OPN production by peripheral blood mononuclear cells infected with Mycobacterium bovis bacillus Calmette-Guérin preceded the synthesis of IL-12 and interferon-gamma and that the neutralizing anti-OPN monoclonal antibody significantly reduced the production of IL-12 and interferon-gamma. Our results suggest that OPN may be involved in the pathologic process associated with active pulmonary tuberculosis by inducing IL-12-mediated type 1 T helper cell responses.

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Objective New serum markers (1 3) β-D-glucan (β-D-glucan) and Results The detection rates of serum β-D-glucan and KL-6 levels in non-HIV PCP were lower than those in HIV PCP (88% vs. 100%, 66% vs. 88%, respectively). The false positive rates of these markers in both groups were similar (12%, 37%, respectively). Oxygenation index, serum albumin, and mechanical ventila-

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 ؋ 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.Legionella pneumophila is the major etiologic agent of Legionnaires' disease, a potentially fatal type of pneumonia affecting immunocompromised and immunocompetent subjects (28,30). This gram-negative bacterium can multiply within the mononuclear cells in vivo and in vitro (6, 14) and evades phagosome-lysosome fusion within these cells (3). Several L. pneumophila virulence factors that facilitate intracellular growth have been identified in screenings with macrophages or in an in vivo screening system with signature-tagged mutagenesis (12). One important set of virulence factors is the dot/icm system, which is a type IV secretion system and is required for evasion of phagosome-lysosome fusion (5, 37, 38) and for the establishment of phagosomes permissive for the growth of L. pneumophila within them (8). However, the effector molecule(s) of this system remains undetermined. The innate immunity to L. pneumophila has been extensively studied. The A/J mouse strain is permissive for the intracellular growth of L. pneumophila (48), whereas other inbred strains of mice, such as BALB/c (49), 57BL/6, and 129X1 (10), are not. In terms of permissiveness of A/J macrophages, the genetic determinant of this permissiveness has been confirmed to be within the Lgn locus, and specifically the Bircle/Naip5 gene (4, 9, 10, 40, 52, 53). However, the role of this gene in regulation of intracellular growth of the bacterium is still unknown.Toll-like receptors (TLRs) have been identified as receptors of pathogen-as...

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Japan Medical Association Center for Clinical Trials JMA-IIA00146.