|PDF Version||Innate Host Defense and Inflammation|
|Director : Chignard Michel (email@example.com)|
Our studies deal with innate defense and inflammation of the lung and are performed with different in vitro approaches as well as with animal models. We investigate in such a pathophysiological context the role of epithelial cells, alveolar macrophages, neutrophils and their receptors (Toll-like receptors (TLR), proteinase-activated receptors (PAR) and CD87). Another aspect of our research deals with the effect of surfactant on alveolar macrophages (synthesis of phospholipases A2 (PLA2), IL-10 and TNF-a) as well as the interaction of PLA2 with the surfactant-protein A (SP-A) (see figure).
The lung is the site of various diseases for which the mechanisms of innate defense and lung inflammation play a major role. Acute respiratory distress syndrome (ARDS), chronic obstructive pulmonary disease (COPD), cystic fibrosis or invasive pulmonary aspergillosis are typical lung inflammatory diseases. The induction of innate defense is a beneficial process but its exacerbation may lead to a pathologic inflammatory status. Therefore, the major aim of our research is to contribute to the qualitative and quantitative understanding of the mechanisms involved in these diseases, which would allow to target the events enhancing innate immunity without exacerbating the inflammatory process.
Cellular interactions in pulmonary airspaces (Michel Chignard, Dominique Pidard and Mustapha Si-Tahar)
During the respiratory cycle, the airways are exposed to numerous particles and microbes. Cells of the immune system interact with these potentially infectious elements through cell surface structures, including the TLR. Among the ten known mammalian TLR, TLR2 and TLR4 have been the best characterized. The lung is also protected by a unique local immunoregulatory system, i.e. the epithelium-derived surfactant. The major surfactant protein, the collectin SP-A, is able to modulate cytokine secretion. Recently, we obtained evidence that the activation by SP-A of the transcription factor NF-kB and of the secretion of cytokines such as TNF-a and IL-10 involve TLR4. Besides, we detected TLR4 and TLR2 expression by several human pulmonary epithelial cell lines and observed that these cells are responsive to stimulation by lipopolysaccharides (LPS) and lipoteichoic acid, two microbial ligands of TLR4 and TLR2, respectively.
Macrophages and polymorphonuclear neutrophils participate actively to inflammatory and infectious pulmonary diseases. Concerning neutrophils, three secretable serine proteinases particularly account for their effects, namely elastase, cathepsin G and proteinase 3. We have focused our research on the analysis of the effects of these proteinases on different membrane receptors involved in the innate defense and inflammatory processes. Current studies show an effect of elastase and cathepsin G on leukocytes themselves, through their capacity to proteolytically lower the membrane expression of CD87/uPAR (urokinase-type plasminogen activator receptor), a glycoprotein also expressed by epithelial cells, and involved in mechanisms of cell adhesion and migration, as well as in tissue repair. Experiments have revealed that these proteinases also cleave PAR-2, a receptor expressed at the surface of pulmonary epithelial cells. Such a receptor, for which the (patho)physiological agonist(s) are not yet characterized, is most likely involved in the mechanisms of innate defense and inflammation. We also demonstrated, in a collaborative work with the Viral Immunity Unit, that elastase inhibits the activity of CXCR4 as well as that of its ligand, the chemokine SDF-1, a pair which can play a role in the pathogenesis of infectious and inflammatory diseases, notably within the lungs. Our current studies consider also the potential activity of bacterial proteinases on these receptors.
Using a murine experimental model, we showed that administration of LPS in the airways triggers neutrophil migration whose presence correlates with an anti-elastase activity. We established that this activity is due to DNA, and is recovered from the airspaces of ARDS patients. The neutrophil influx is partly due to TNF-a produced by LPS-activated alveolar macrophages. Unexpectedly, these activated macrophages are unable to synthesize IL-10, an anti-inflammatory cytokine. SP-A may explain this particular phenotype as we showed that this protein is able to down-regulate IL-10 production by cells from the monocytic lineage. Interestingly, during an experimental lethal pulmonary infection with Aspergillus fumigatus (collaboration with the Aspergillus Unit), IL-10 is detected in the airspaces and such a production could play a role in animal mortality. Our current studies demonstrate the involvement of TLR2 and TLR4 in this pathology as mice deficient for one of these two receptors are more susceptible to infection.
Mechanisms of regulation and roles of phospholipase A2 in lung inflammatory diseases (Lhousseine Touqui)
PLA2 catalyse the hydrolysis of phospholipids at the sn-2 position, leading to the generation of cytotoxic lysophospholipids and free fatty acids such as arachidonic acid (AA). The latter is the precursor of leukotrienes and prostaglandins endowed with various biological activities and involved in a number of inflammatory diseases. Moreover, hydrolysis of cell membrane phospholipids by PLA2 induces the reorganisation of the structure of these membranes and changes of their physico-chemical properties. Recent studies showed the existence of several types of PLA2 whose genes have been cloned and classified in several families including intracellular and secretory PLA2 (sPLA2). The type IIA sPLA2 (sPLA2-IIA) is suggested to play a significant role in different human inflammatory diseases, such as allergic rhinitis, rhumatoïd arthritis, septic shock or ARDS. We developed an animal model which reproduces the anatomopathological criteria of human ARDS. This model is based on the intratracheal administration of LPS to guinea pigs. We showed that LPS causes an acute pulmonary inflammation accompanied by an increased expression of sPLA2-IIA and its release in the alveolar space. Alveolar macrophages are the main source of this enzyme whose expression is induced by an autocrine/paracrine process mediated by TNF-a. Stimulation of sPLA2-IIA synthesis by LPS is due to induction of the expression of this enzyme at the transcriptional level via a process involving the activation of the transcriptional factor NF-kB. In contrast, another transcription factor, the peroxisome proliferator activated receptor-g (PPAR-g) inhibits sPLA2-IIA expression. Recent results demonstrated that AA down-regulates the expression of sPLA2-IIA mainly via its cyclooxygenase-dependent metabolites and through the inhibition of NF-kB activation. AA can also down-regulates sPLA2-IIA expression by a cyclooxygenase-independent mechanism, involving the activation of PPAR-g. Finally, we showed that sPLA2-IIA is involved in the hydrolysis of surfactant phospholipids and suggested that this process may play a role in the deterioration of the pulmonary surfactant. Similar results were obtained using another model of ARDS induced by intratracheal instillation of Pseudomonas aeruginosa to rat. This deterioration is a typical characteristic of ARDS, leading to the permanent affixing of the alveolar walls, thus blocking the diffusion of oxygen. We also showed that hydrolysis of surfactant phospholipids is controlled by SP-A, which inhibits the catalytic activity of sPLA2-IIA via a specific and calcium-dependent interaction. Thus, hydrolysis of surfactant phospholipids was enhanced both in vitro and in vivo in SP-A -/- mice as compared to wild-type mice. SP-A was also able to inhibit the enzymatic activity of sPLA2-V and -X, but not that of sPLA2-IB, -IID and -IIE. These properties of SP-A may represent a mechanism by which the lung protects surfactant against the deleterious effect of sPLA2.
Keywords: innate defense/inflammation, epithelial cells, neutrophils, macrophages, Toll-like receptors, proteinases phospholipases A2, surfactant, lung
|Publications of the unit on Pasteur's references database|
|Office staff||Researchers||Scientific trainees||Other personnel|
|Villeneuve Josiane (firstname.lastname@example.org)||Chignard Michel, Inserm (DR1,email@example.com)
Pidard Dominique, CNRS (CR1,firstname.lastname@example.org)
Si-Tahar Mustapha, Inserm (CR2,email@example.com)
Touqui Lhousseine, IP (CR,firstname.lastname@example.org)
|Beaufort Nathalie PhD student (email@example.com)
Chabot Sophie PhD student (firstname.lastname@example.org)
Dulon Sophie PhD student (email@example.com)
Guillot Loïc PhD student (firstname.lastname@example.org)
Medjane Samir PhD student (email@example.com )
Wu Yongzheng Postdoc (firstname.lastname@example.org)
|Balloy Viviane (Technician Inserm,email@example.com)
Leduc Dominique (Technician IP,firstname.lastname@example.org)
Thouron Françoise (Technician IP,email@example.com)