Christian Vesin

Expression of a tumor necrosis factor-alpha transgene in murine lung causes lymphocytic and fibrosing alveolitis. A mouse model of progressive pulmonary fibrosis.

The murine TNF-alpha gene was expressed under the control of the human surfactant protein SP-C promoter in transgenic mice. A number of the SP-C TNF-alpha mice died at birth or after a few weeks with very severe lung lesions. Surviving mice transmitted a pulmonary disease to their offspring, the severity and evolution of which was related to the level of TNF-alpha mRNA in the lung; TNF-alpha RNA was detected in alveolar epithelium, presumably in type II epithelial cells. In a longitudinal study of two independent mouse lines, pulmonary pathology, at 1-2 mo of age, consisted of a leukocytic alveolitis with a predominance of T lymphocytes. Leukocyte infiltration was associated with endothelial changes and increased levels of mRNA for the endothelial adhesion molecule VCAM-1. In the following months, alveolar spaces enlarged in association with thickening of the alveolar walls due to an accumulation of desmin-containing fibroblasts, collagen fibers, and lymphocytes. Alveolar surfaces were lined by regenerating type II epithelial cells, and alveolar spaces contained desquamating epithelial cells in places. Platelet trapping in the damaged alveolar capillaries was observed. Pulmonary pathology in the SP-C TNF-alpha mice bears a striking resemblance to human idiopathic pulmonary fibrosis, in which increased expression of TNF-alpha in type II epithelial cells has also been noted. These mice provide a valuable animal model for understanding the pathogenesis of pulmonary fibrosis and exploring possible therapeutic approaches.

Interleukin 1 receptor antagonist (IL-1ra) prevents or cures pulmonary fibrosis elicited in mice by bleomycin or silica.

We explored the role of interleukin 1 (IL-1) in two models of pulmonary fibrosis (PF), elicited in mice by the intra-tracheal instillation of bleomycin or silica. In both models, administration of IL-1 receptor antagonist (IL-1ra) by an osmotic minipump implanted i.p., at a rate of 0.5 microgram/h, completely prevented the collagen deposition, as evaluated by the lung hydroxyproline content on day 15 after instillation. IL-1ra had little or no influence on the number of cells recovered from the broncho-alveolar lavage. Study of histological sections suggests that IL-1ra globally decreased the proportion of damaged lung and particularly in silica the formation of nodules with a rich content in collagen fibrils. IL-1ra was also effective in reducing the lung hydroxyproline content when given on day 25 after instillation of bleomycin or silica, indicating that it may reverse established PF. This study indicates that IL-1ra might be useful for the treatment of incipient or established pulmonary fibrosis.

Keratinocyte Growth Factor Protects Alveolar Epithelium and Endothelium from Oxygen-Induced Injury in Mice

Keratinocyte growth factor (KGF) has been used successfully to prevent alveolar damage induced by oxygen exposure in rodents. However, this treatment was used intratracheally and before oxygen exposure, which limited its clinical application. In the present study, mice were treated with the recombinant human KGF intravenously before (days -2 and -1) or during (days 0 and +1) oxygen exposure. In both cases, lung damage was attenuated. KGF increased the number of cells incorporating bromodeoxyuridine (BrdU) in the septa and in bronchial epithelium of air-breathing mice but not of oxygen-exposed mice, indicating that the protective effect of KGF is not necessarily associated with proliferation. Oxygen-induced damage of alveolar epithelium and, unexpectedly, of endothelium was prevented by KGF treatment as seen by electron microscopy. We investigated the effect of KGF on different mechanisms known to be involved in oxygen toxicity. The induction of p53, Bax, and Bcl-x mRNAs during hyperoxia was to a large extent prevented by KGF. Surfactant proteins A and B mRNAs were not markedly modified by KGF. The anti-fibrinolytic activity observed in the alveoli during hyperoxia was to a large extent prevented by KGF, most probably by suppressing the expression of plasminogen activator inhibitor-1 (PAI-1) mRNA and protein. As PAI-1 -/- mice are more resistant to hyperoxia, KGF might act, at least in part, by decreasing the expression of this protease inhibitor and by restoring the fibrinolytic activity into the lungs.

TNF-induced enterocyte apoptosis in mice is mediated by the TNF receptor 1 and does not require p53.

Injection of recombinant mouse TNF into mice is known to induce a shrinkage of the duodenal villi, which becomes evident 30 – 90 min later and is associated with a detachment of enterocytes in the lumen. These cells can be collected by lavage and are all apoptotic, i.e. hypodiploid as seen by flow cytometric analysis. Thus the count of detached cells was used as an evaluation of the TNF‐induced cell loss and apoptosis in the mucosa. TNF injection induced a cell loss of similar magnitude in wild‐type (+/+) or in mice lacking the TNF receptor (TNFR)2 (p75, TNFR2 −/−), while mice lacking the TNFR1 (p55, TNFR1 −/−) were completely resistant to this effect. TNF increased the expression of p53 tumor suppressor gene in the enterocytes from the crypts but not from the villi, as seen by Western blots and histochemistry. TNF increased the expression of p53 in both TNFR2 −/− and TNFR1 −/− mice. Furthermore, enterocyte cell loss was not attenuated in p53 −/− mice. The results indicate that TNF, acting on its receptor 1, induces an apoptotic detachment of the enterocytes from the tip of the villi ( i.e. the old enterocytes), while in the enterocytes from the crypts (the young enterocytes) TNF increases, via either TNFR1 or TNFR2, the expression of p53, without inducing apoptosis.

Indirect Effects of Leptin Receptor Deficiency on Lymphocyte Populations and Immune Response in db/db Mice

Leptin-deficient ob/ob and leptin receptor (Ob-rb)-deficient db/db mice display a marked thymic atrophy and exhibit defective immune responses. Lymphocytes express leptin receptors and leptin exerts direct effects on T cells in vitro. In addition, ob/ob and db/db mice display multiple neuroendocrine and metabolic defects, through which leptin deficiency may indirectly affect the immune system in vivo. To study the relative contributions of direct and indirect effects of leptin on the immune system in a normal environment, we generated bone marrow chimeras (BMCs) by transplantation of leptin receptor-deficient db/db, or control db/+, bone marrow cells into wild-type (WT) recipients. The size and cellularity of the thymus, as well as cellular and humoral immune responses, were similar in db/db to WT and db/+ to WT BMCs. The immune phenotype of db/db mice is thus not explained by a cell autonomous defect of db/db lymphocytes. Conversely, thymus weight and cell number were decreased in the reverse graft setting in WT to db/db BMCs, indicating that expression of the leptin receptor in the environment is important for T cell development. Finally, normal thymocyte development occurred in fetal db/db thymi transplanted into WT hosts, indicating that direct effects of leptin are not required locally in the thymic microenvironment. In conclusion, direct effects of leptin on bone marrow-derived cells and on thymic stromal cells are not necessary for T lymphocyte maturation in normal mice. In contrast, leptin receptor deficiency affects the immune system indirectly via changes in the systemic environment.

Thrombocytopenia in an animal model of malaria is associated with an increased caspase-mediated death of thrombocytes

Infection of mice with Plasmodium Berghei Anka (PbA) leads to a thrombocytopenia, due to a reduced platelet life span, eventually associated with a syndrome of severe or cerebral malaria (CM). Thrombocytopenia was associated with an increase in the number of microparticles (mcp) in plasma. More than >60% of these mcp were of platelet origin, as seen by staining with an anti-platelet antibody. The thrombocytopenia and the amount of mcp were decreased in mice treated with anti CD40L mAb, suggesting that CD40L is the main effector of the thrombocytopenia. Caspase-1, -3, -6, -8, -9 were activated in platelets from infected mice, as seen by the binding of labeled probes or the amount of pro-caspase-3. Treatment of infected mice with the caspases inhibitor ZVAD-fmk decreased the number of mcp and the thrombocytopenia, shoving that platelet caspases are responsible for platelet fragmentation. In addition, the caspase inhibitor also caused a decrease in the mortality associated with CM, indicating a critical role of caspases in the expression of CM.

Role of CD40-CD40L in Mouse Severe Malaria

We explored the role of CD40-CD40L (CD154) in the severe malaria elicited by Plasmodium berghei anka infection in mice. Mortality was >90% by day 8 after infection in +/+ mice, but markedly decreased in CD40-/- or in CD40L-/- mice, as well as in +/+ mice treated with anti-CD40L monoclonal antibody. Parasitemia was similar in the different conditions. Breakdown of the blood-brain barrier was evident in infected +/+, but not in CD40-/- mice. Thrombocytopenia was less severe in CD40-/- mice than in the +/+ controls. Sequestration of macrophages in brain venules and alveolar capillaries was reduced in CD40-/- or in CD40L-/- mice, whereas sequestration of parasitized red blood cells or polymorphonuclear leukocytes in alveolar capillaries was CD40-CD40L-independent. CD40 mRNA was increased in the brain and lung of infected mice whereas CD40L was increased in the lung. Tumor necrosis factor plasma levels were similarly increased in infected +/+ or CD40-/- mice. Expression of CD54 and its mRNA levels in the brain were moderately decreased in CD40-deficient mice. Thus the mortality associated with severe malaria requires CD40-CD40L interaction that contributes to the breakdown of the blood-brain barrier, macrophage sequestration, and platelet consumption.

Delayed Mortality and Attenuated Thrombocytopenia Associated with Severe Malaria in Urokinase- and Urokinase Receptor-Deficient Mice

ABSTRACT We explored the role of urokinase and tissue-type plasminogen activators (uPA and tPA), as well as the uPA receptor (uPAR; CD87) in mouse severe malaria (SM), using genetically deficient (−/−) mice. The mortality resulting from Plasmodium berghei ANKA infection was delayed in uPA−/− and uPAR−/−mice but was similar to that of the wild type (+/+) in tPA−/− mice. Parasitemia levels were similar in uPA−/−, uPAR−/−, and +/+ mice. Production of tumor necrosis factor, as judged from the plasma level and the mRNA levels in brain and lung, was markedly increased by infection in both +/+ and uPAR−/− mice. Breakdown of the blood-brain barrier, as evidenced by the leakage of Evans Blue, was similar in +/+ and uPAR−/− mice. SM was associated with a profound thrombocytopenia, which was attenuated in uPA−/− and uPAR−/− mice. Administration of aprotinin, a plasmin antagonist, also delayed mortality and attenuated thrombocytopenia. Platelet trapping in cerebral venules or alveolar capillaries was evident in +/+ mice but absent in uPAR−/− mice. In contrast, macrophage sequestration in cerebral venules or alveolar capillaries was evident in both +/+ and uPAR−/− mice. Polymorphonuclear leukocyte sequestration in alveolar capillaries was similar in +/+ and uPAR−/− mice. These results demonstrate that the uPAR deficiency attenuates the severity of SM, probably by its important role in platelet kinetics and trapping. These results therefore suggest that platelet sequestration contributes to the pathogenesis of SM.

Role of the Tumor Necrosis Factor Receptor 2 (TNFR2) in Cerebral Malaria in Mice

Infection of susceptible mice with Plasmodium berghei Anka leads to a syndrome of severe or cerebral malaria. Tumor necrosis factor (TNF) contributes to this syndrome, apparently by acting on its receptor 2 (TNFR2) because TNFR1-/- are susceptible, whereas TNFR2-/- mice are resistant. In this work, we confirmed the essential role of the TNFR2 in cerebral malaria because 6 to 8 days after Plasmodium berghei Anka infection, hypothermia, coma, and death were observed in +/+ or TNFR1-/-, but never in TNFR2-/-, mice. TNF production, evaluated by the serum levels or the mRNA levels in the brain, spleen or lung, was similar in +/+, TNFR1-/-, or TNFR2-/- mice. Macrophage or parasitized red blood cell sequestration in brain or lung was similar in TNFR1-/- and TNFR2-/- mice. Accordingly, up-regulation of CD54 or CD40 in brain or lung was also similar in TNFR1-/- or TNFR2-/- mice. Platelet loss, manifested by thrombocytopenia and the presence of microparticles in plasma, was similar in TNFR1-/- or TNFR2-/- mice. Breakdown of the blood–brain barrier, detected by the diffusion of tracers, was attenuated in both TNFR1-/- and TNFR2-/-, compared with +/+, mice. Endothelial cells from brain capillaries, examined by transmission electron microscopy, were similar in infected TNFR1-/- or TNFR2-/- mice, whereas the basement membrane was enlarged in TNFR1-/- mice. Hypothermic mice were also hyperglycemic, and this was evident in +/+ and TNFR1-/-, but not in TNFR2-/-, mice. In addition, infected +/+ and TNFR1-/- mice became insulin resistant, while in contrast TNFR2-/- became extremely insulin sensitive. This study supports the possibility that coma and death are mediated not by cell sequestration or breakdown of vascular permeability, similar in TNFR1-/- or TNFR2-/- mice, but by metabolic disturbances selectively mediated by the TNFR2.

Modulation of platelet caspases and life-span by anti-platelet antibodies in mice.

Abstract: Anti‐platelet antibodies are known to contribute to some types of thrombocytopenia. In this work we investigated anti‐platelet antibodies with opposite influence upon activation and kinetics of platelet caspases. A rabbit anti‐platelet antibody induced a profound thrombocytopenia, which was associated with an increase of microparticles in plasma and an activation of platelet caspases, as detected by the binding of a carboxyfluorescein‐labeled fluoromethyl ketone probe (FAM‐VAD‐fmk). Furthermore, microparticles and thrombocytopenia were prevented by the injection of a caspase inhibitor ZVAD‐fmk. In contrast, an anti‐CD18 mAb (M18.2) induced a thrombocytosis, due to an increased platelet life‐span and which was evident in wild‐type (+/+), but not in CD18−/− or CD87−/−, mice indicating a requirement of these two surface molecules. Activation of caspases was decreased in platelets from mice injected with the M 18.2 mAb, as evidenced by a decreased binding of the VAD probe, detected by flow cytometry, or an increase in the level of pro‐caspase‐3, seen on Western blots. These observations indicate firstly, that anti‐platelet antibodies can either promote or inhibit activation of platelet caspases, and secondly, that the activation of caspases regulates platelet life‐span.