Elsevier

Cytokine

Volume 44, Issue 2, November 2008, Pages 298-303
Cytokine

TNF receptor 1 and 2 contribute in different ways to resistance to Legionella pneumophila-induced mortality in mice

https://doi.org/10.1016/j.cyto.2008.08.015Get rights and content

Abstract

Legionella pneumophila is one of the most important pathogens which cause community-acquired pneumonia. Although TNF-α is considered to play an important role in response to bacteria, the role of the TNF-α receptor on L. pneumophila infection remains to be elucidated. To investigate this, we infected TNF receptor deficient mice with L. pneumophila. L. pneumophila was inoculated intranasally into TNF receptor (TNFR)-1-knock-out mice or TNFR2-knock-out mice. The mortality rate, histology of the lung, bacterial growth in the lung, and bronchoalveolar lavage (BAL) fluids were investigated. The bacterial growth of L. pneumophila in the macrophages was also studied. Almost all the mice survived after an intranasal inoculation of 1 × 106 CFU/head of L. pneumophila, but more than 90% mice were killed after inoculation of 1 × 108 CFU/head of L. pneumophila. In the case of TNFR1-knock-out mice and TNFR2-knock-out mice, a high mortality rate was observed after inoculation of 1 × 107 CFU/head of L. pneumophila in comparison to wild-type mice. The lung histology from both the TNFR1-knock-out mice documented severe lung injury at day 3 after inoculation. The clearance of L. pneumophila in the lung of the TNFR1-knock-out mice was slower than those from both the TNFR2-knock-out mice and the wild-type mice. Moreover, L. pneumophila growth in the peritoneal macrophages from the TNFR1-knock-out mice was observed. Interestingly, a lack of neutrophils accumulation in the BAL fluids and a dysregulation of cytokines (IFN-γ, interleukin-12, and TNF-α) were observed in the TNFR1-knock-out mice. On the contrary, large accumulation of neutrophils in BAL fluids was observed in TNFR2-knock-out mice. These data suggested that a TNFR1 deficiency led to a compromise of the innate immunity against L. pneumophila, while a TNFR2 deficiency induced an excessive inflammatory response and resulted in death. The present study confirmed that TNFR1 and TNFR2 play a crucial, but different role in the control of L. pneumophila-induced mortality.

Introduction

Tumor necrosis factor (TNF)-α is a pleiotropic cytokine which plays a critical role in controlling a vast array of immunological responses in the host defense. TNF-α is synthesized as a non-glycosylated, transmembrane protein, and then it undergoes cleavage by the specific metalloproteinase TNF-converting enzyme to form a soluble trimer. TNF-α binds to its two kinds of receptors (TNFR1 and TNFR2), present on virtually all cells throughout the body, and evokes a variety of reactions [1], [2], [3]. TNF-α contributes to innate immunity against intracellular proliferating bacilli such as Mycobacterium tuberculosis or Listeria monocytogenes [4], [5], [6], [7].

Legionella pneumophila has been recognized as a common pathogen of community-acquired pneumonia since 1976. The prevalence is reported to range from 1% to 30% in community-acquired pneumonia. This pathogen causes life-threatening pneumonia [8], [9]. Since L. pneumophila proliferates within host cells similar to M. tuberculosis or L. monocytogenes, TNF-α has been considered to play a critical role in the innate immunity against L. pneumophila. The secretion of TNF-α is an important autocrine defense mechanism of alveolar macrophages against L. pneumophila [10]. The neutrophils activated by the TNF-α contribute to the eradication of bacteria from infected lung tissues, thereby protecting the host [11]. In fact, the administration of TNF-α antibody has been reported to worsen L. pneumophila infection [12]. There is a clinical case report of L. pneumophila pneumonia occurring after infliximab, TNF antagonist, therapy for rheumatoid arthritis [13]. Such evidence clearly supports the importance of TNF-α in the immune response. However, the role of TNFR1 or TNFR2 on Legionella infection has not yet been clarified.

In this study, we investigated the role of TNFR in the host defense against L. pneumophila using TNFR1- or TNFR2-deficient mice. As a result, the important role of the TNF receptors in lung inflammation induced by L. pneumophila has been confirmed.

Section snippets

Bacteria

The Legionella spp. were obtained from the Gifu Type Culture Collection (GTC). The L. pneumophila Bloomington-2 strain (GTC 9137) and Philadelphia-1 strain (GTC 9134) were used. All strains were grown in buffered yeast extract (BYE) broth at 37 °C with shaking or on buffered charcoal yeast extract agar (BCYE; BYE with 0.2% activated charcoal and 1.5% Bacto agar) at 37 °C for 3 days. Both types of media were supplemented with 0.4-g/l of l-cysteine and 0.25-g/l ferric pyrophosphate, and the pH was

Results

The role of TNF-α on L. pneumophila infection was investigated using TNFR-deficient mice in vivo. After the intranasal instillation of 1 × 106 CFU/head of L. pneumophila, almost all the mice survived. All the mice died after 1 × 108 CFU/head of L. pneumophila inoculation. The TNFR1-KO mice and the TNFR2-KO mice demonstrated a high mortality rate in comparison to the wild-type mice after 1 × 107 CFU/head of L. pneumophila inoculation (Fig. 1).

The lung histology at day 1 after 1 × 107 CFU/head of L.

Discussion

TNF-α has been reported to play an important role in protective immunity against intracellularly proliferating bacteria such as L. pneumophila [4], [5], [6], [7]. The induction of TNF by L. pneumophila is involved in host defense, and the neutrophils activated by the TNF could clear the organism from the lung tissues, thereby protecting the animal [11]. Although the importance of TNF-α is evident, the role of its receptor remains uncleared issue. In the present study, the role of the TNF

Acknowledgments

We appreciate the assistance of Dr. Brian Quinn for editing the English usage.

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