Anne H. Fortier

The Nod-Like Receptor Family Member Naip5/Birc1e Restricts Legionella pneumophila Growth Independently of Caspase-1 Activation

Similar to Ipaf and caspase-1, the Nod-like receptor protein Naip5 restricts intracellular proliferation of Legionella pneumophila, the causative agent of a severe form of pneumonia known as Legionnaires’ disease. Thus, Naip5 has been suggested to regulate Legionella replication inside macrophages through the activation of caspase-1. In this study, we show that cytosolic delivery of recombinant flagellin activated caspase-1 in A/J macrophages carrying a mutant Naip5 allele, and in C57BL/6 (B6) macrophages congenic for the mutant Naip5 allele (B6-Naip5A/J), but not in Ipaf−/− cells. In line with these results, A/J and B6-Naip5A/J macrophages induced high levels of caspase-1 activation and IL-1β secretion when infected with Legionella. In addition, transgenic expression of a functional Naip5 allele in A/J macrophages did not alter Legionella-induced caspase-1 activation and IL-1β secretion. Notably, defective Naip5 signaling renders B6-Naip5A/J macrophages permissive for Legionella proliferation despite normal caspase-1 activation. These results indicate that the restriction of intracellular Legionella replication is more complex than previously appreciated and requires both Ipaf-dependent caspase-1 activation as well as functional Naip5 signaling.

Administration of a liposomal FGF-2 peptide vaccine leads to abrogation of FGF-2-mediated angiogenesis and tumor development

Basic fibroblast growth factor (FGF-2) is an important stimulator of angiogenesis that has been implicated in neoplastic progression. Attempts to neutralize or modulate FGF-2 have met with some success in controlling neovascularity and tumor growth. In the present study, two peptides: one corresponding to the heparin binding domain and the other to the receptor binding domain of FGF-2, exerted dose-dependent inhibition of FGF-2-stimulated human umbilical vein endothelial cell proliferation (IC(50)=70 and 20 microg/ml, respectively). The identification of these functional regions suggested that targeting these domains might be an approach for the modulation of FGF-2 function. To investigate this possibility, we vaccinated mice with either the heparin binding domain peptide or the receptor binding domain peptide of FGF-2 in a liposome/adjuvant format, and analyzed the effect of vaccination on FGF-2-driven angiogenesis, tumor development and immune status. Mice vaccinated with the heparin binding domain peptide generated a specific antibody response to FGF-2, blocked neovascularization in a gelfoam sponge model of angiogenesis, and inhibited experimental metastasis by >90% in two tumor models: the B16BL6 melanoma and the Lewis lung carcinoma. These effects were not observed in mice treated with the receptor binding domain peptide conjugated to liposomes or liposomes lacking conjugated peptide. These data suggest that a heparin binding domain peptide of FGF-2, when presented to a host in a liposomal adjuvant formulation, can ultimately lead to inhibition of angiogenesis and tumor growth.

Birc1e/Naip5 rapidly antagonizes modulation of phagosome maturation by Legionella pneumophila

Legionella survives intracellularly by preventing fusion with lysosomes, due to phagosome escape from the endocytic pathway at an early stage of phagosome maturation, and by creating a replicative organelle that acquires endoplasmic reticulum (ER) characteristics through sustained interactions and fusion with the ER. Intracellular replication of Legionella pneumophila in mouse macrophages is controlled by the Lgn1 locus. Functional complementation in vivo has identified the Birc1e/Naip5 gene as being responsible for the Lgn1 effect. To understand the function and temporal site of action of Birc1e/Naip5 in susceptibility to L. pneumophila, we examined the biogenesis of Legionella‐containing vacuoles (LCVs) formed in permissive A/J macrophages and in their Birc1e/Naip5 transgenic non‐permissive counterpart. Birc1e/Naip5 effects on acquisition of lysosomal and ER markers were evident within 1–2 h following infection. A significantly higher proportion of LCVs formed in Birc1e/Naip5 transgenic macrophages had acquired the lysosomal markers cathepsin D and Lamp1 by 2 h post infection, whereas a significantly higher proportion of LCVs formed in permissive macrophages were positively stained for the ER markers BAP31 and calnexin, 6 h post infection. Likewise, studies by electron microscopy showed acquisition of lysosomal contents (horseradish peroxidase), within the first hour following phagocytic uptake, by LCVs formed in Birc1e/Naip5 transgenic macrophages and delivery of the ER marker glucose 6‐phosphatase (G6Pase) only to the lumen of LCVs formed in A/J macrophages. Finally, a larger proportion of LCVs formed in A/J macrophages were studded with ribosomes 24 h post infection, compared with LCVs formed in Birc1e/Naip5 transgenic macrophages. These results suggest that sensing of L. pneumophila products by Birc1e/Naip5 in macrophages occurs rapidly following phagocytosis, a process that antagonizes the ability of L. pneumophila to remodel its phagosome into a specialized vacuole with ER characteristics.

Single gene effects in mouse models of host: pathogen interactions

Inbred mouse strains have been known for many years to vary in their degree of susceptibility to different types of infectious diseases. The genetic basis of these interstrain differences is sometimes simple but often complex. In a few cases, positional cloning has been used successfully to identify single gene effects. The natural resistance‐associated macrophage protein 1 (Nramp1) gene (Slc11a1) codes for a metal transporter active at the phagosomal membrane of macrophages, and Nramp1 mutations cause susceptibility to Mycobacterium, Salmonella, and Leishmania. Furthermore, recent advances in gene transfer technologies in transgenic mice have enabled the functional dissection of gene effects mapping to complex, repeated parts of the genome, such as the Lgn1 locus, causing susceptibility to Legionella pneumophila in macrophages. Finally, complex traits such as the genetically determined susceptibility to malaria can sometimes be broken down into multiple single gene effects. One such example is the case of pyruvate kinase, where a loss‐of‐function mutation was recently shown by our group to be protective against blood‐stage infection with Plasmodium chabaudi. In all three cases reviewed, the characterization of the noted gene effect(s) has shed considerable light on the pathophysiology of the infection, including host response mechanisms.

Zinc ligand-disrupted recombinant human Endostatin: Potent inhibition of tumor growth, safety and pharmacokinetic profile

Endostatin, a potent endogenous inhibitor of angiogenesis, inhibits the growth of primary tumors without induction of acquired drug resistance in mice. We report that a soluble recombinant human (rh) Endostatin produced with characteristics of the native Endostatin, effectively inhibited the growth of primary tumors and pulmonary metastases in a dose-dependent manner. We also show that deletion of two of the four zinc ligands of rhEndostatin did not affect this potent tumor inhibiton. The growth of established Lewis lung primary tumors implanted into mice was inhibited (80–90%) upon systemic treatment with 50 mg/kg/12 h of rhEndostatin. Using the B16-BL6 murine experimental pulmonary metastases model, rhEndostatin administered at 1.5 mg/kg/day or 4.5 mg/kg/day beginning 3- or 11-days post tumor cell injection, respectively, resulted in an approximate 80% inhibition of tumor growth. At effective anti-tumor doses of 1.5 and 50 mg/kg, pharmacokinetic modeling in mice showed (a) the protein was 100% bioavailable, (b) the AUC ranged from 16 to 700 ngml/h and (c) the Cmax ranged from 161 to 4582 ng/ml. At the highest dose tested (300 mg/kg), delivered as a single bolus, no drug-related toxicity was observed in a Cynomolgus monkey infused with rhEndostatin. No toxicity was observed even at AUC and Cmax values that were 1.3- to 56-fold higher than those observed in mice with tumors that were potently inhibited. Our production system yields a well characterized, soluble and potent rhEndostatin at quantities sufficient for human use. The preclinical studies described herein are an important first step toward the assessment of Endostatin in the clinic.

Restriction of Legionella pneumophila Replication in Macrophages Requires Concerted Action of the Transcriptional Regulators Irf1 and Irf8 and Nod-Like Receptors Naip5 and Nlrc4

ABSTRACT The unique permissiveness of A/J mouse macrophages for replication of Legionella pneumophila is caused by a deficiency in the Nod-like receptor (NLR) protein and intracellular sensor for L. pneumophila flagellin (Naip5). The signaling pathways and proteins activated by Naip5 sensing in macrophages were investigated. Transcript profiling of macrophages from susceptible A/J mice and from resistant A/J mice harboring a transgenic wild-type copy of Naip5 at 4 h following L. pneumophila infection suggested that two members of the Irf transcriptional regulator family, Irf1 and Irf8, are regulated in response to Naip5 sensing of L. pneumophila. We show that macrophages having defective alleles of either Irf1 (Irf1−/−) or its heterodimerization partner gene Irf8 (Irf8R294C) become permissive for L. pneumophila replication, indicating that both the Irf1 and Irf8 proteins are essential for macrophage defense against L. pneumophila. Moreover, macrophages doubly heterozygous (Naip5AJ/WT Irf8R294C/WT or Nlrc4−/+Irf8R294C/WT) for combined loss-of-function mutations in Irf8 and in either Naip5 or Nlrc4 are highly susceptible to L. pneumophila, indicating that there is a strong genetic interaction between Irf8 and the NLR protein family in the macrophage response to L. pneumophila. Legionella-containing phagosomes (LCPs) formed in permissive Irf1−/− or Irf8R294C macrophages behave like LCPs formed in Naip5-insufficient and Nlrc4-deficient macrophages which fail to acidify. These results suggest that, in addition to Naip5 and Nlrc4, Irf1 and Irf8 play a critical role in the early response of macrophages to infection with L. pneumophila, including antagonizing the ability of L. pneumophila to block phagosome acidification. They also suggest that flagellin sensing by the NLR proteins Naip5 and Nlrc4 may be coupled to Irf1-Irf8-mediated transcriptional activation of key effector genes essential for macrophage resistance to L. pneumophila infection.

Global cellular changes induced by Legionella pneumophila infection of bone marrow-derived macrophages

The nucleotide-binding oligomerization domain (Nod)-like receptor (NLR) family member Naip5 plays an essential role in restricting Legionella pneumophila growth inside primary macrophages. Upon interaction with bacterial flagellin, the intracellular receptor Naip5 forms a multi-protein complex, the inflammasome, which activation has a protective role against infection. The A/J mouse strain carries a Naip5 allele (Naip5(A/J)), which renders its macrophages susceptible to Legionella infection. However, Naip5(A/J) is still competent for inflammasome activation suggesting that an as yet unidentified signaling pathway located downstream of Naip5 and defective in Naip5(A/J) macrophages regulates macrophage defenses against Legionella. Therefore, transcriptional profiling experiments with macrophages from C57BL/6J mice (B6), and from congenic mice (BcA75) carrying the partial loss-of-function A/J-derived allele (Naip5(A/J)) on a B6 background, infected or not with wild-type L. pneumophila or flagellin-deficient mutant were carried out to identify genes regulated by flagellin and by Naip5. Both the Legionella infection per se and the presence of flagellin had very strong effects on transcriptional responses of macrophages, 4h following infection, including modulation of cellular pathways associated with inflammatory response and cell survival. On the other hand, the presence of wild type or partial loss of function allele (Naip5(A/J)) at Naip5 did not cause large effects on transcriptional responses of macrophages to infection. We also examined in L. pneumophila infected macrophages, the effect of Naip5 alleles on expression and phosphorylation of 524 phosphoproteins, kinases and phosphatases involved in cell proliferation, immune response, stress and apoptosis. Naip5 alleles had an effect on the TLR-Il1R signaling pathway, the cell cycle and the caveolin-mediated response to pathogen. The results of transcriptome and proteome analyses were organized into cellular pathways in macrophages that are modulated in response to Legionella infection.

Immunotherapy of tularemia: characterization of a monoclonal antibody reactive with Francisella tularensis

An IgM monoclonal antibody (mAb) recognized surface antigens specific to Francisella tularensis wild‐type (Schu4) and live vaccine strain (LVS), and reacted with both in ELISA and slide agglutination tests. This mAb also reacted with LVS microorganisms in tissues of infected mice as assessed by an indirect fluorescence technique. Western blot analysis showed the mAb to react with antigens associated with F. tularensis LPS.