Production of eosinophil chemotactic factor by CD8+ T-cells in Toxocara canis-infected mice

Pseudomonas aeruginosa infection alters the macrophage phenotype switching process during wound healing in diabetic mice

Macrophages play critical roles in wound healing process. They switch from "classically activated" (M1) phenotype in the early inflammatory phase to "alternatively activated" (M2) phenotype in the later healing phase. However, the dynamic process of macrophage phenotype switching in diabetic wounds burdened with bacteria is unclear. In this report, Pseudomonas aeruginosa, frequently detected in diabetic foot ulcers, was inoculated into cutaneous wounds of db/db diabetic mice to mimic bacterium-infected diabetic wound healing. We observed that P. aeruginosa infection impaired diabetic wound healing and quickly promoted the expression of pro-inflammatory genes (M1 macrophage markers) tumor necrosis factor-α (tnf-α), interleukin-1β (il-1β) and il-6 in wounds. The expression of markers of M2 macrophages, including il-10, arginase-1, and ym1 were also upregulated. In addition, similar gene expression patterns were observed in macrophages isolated directly from wounds. Immunostaining showed that P. aeruginosa infection increased both the ratios of M1 and M2 macrophages in wounds compared with that in control groups, which was further confirmed by in vitro culturing macrophages with P. aeruginosa and skin fibroblast conditioned medium. However, the ratios of the expression levels of pro-inflammatory genes to anti-inflammatory gene il-10 was increased markedly in P. aeruginosa infected wounds and macrophages compared with that in control groups, and P. aeruginosa prolonged the presence of M1 macrophages in the wounds. These data demonstrated that P. aeruginosa in diabetic wounds activates a mixed M1/M2 macrophage phenotype with an excessive activation of M1 phenotype or relatively inadequate activation of M2 phenotype.

Type I IL-4Rs selectively activate IRS-2 to induce target gene expression in macrophages

Although interleukin-4 (IL-4) and IL-13 participate in allergic inflammation and share a receptor subunit (IL-4Ralpha), they have different functions. We compared cells expressing type I and II IL-4Rs with cells expressing only type II receptors for their responsiveness to these cytokines. IL-4 induced highly efficient, gammaC-dependent tyrosine phosphorylation of insulin receptor substrate 2 (IRS-2), whereas IL-13 was less effective, even when phosphorylation of signal transducer and activator of transcription 6 (STAT6) was maximal. Only type I receptor, gammaC-dependent signaling induced efficient association of IRS-2 with the p85 subunit of phosphoinositide 3-kinase or the adaptor protein growth factor receptor-bound protein 2. In addition, IL-4 signaling through type I IL-4Rs induced more robust expression of a subset of genes associated with alternatively activated macrophages than did IL-13. Thus, IL-4 activates signaling pathways through type I IL-4Rs qualitatively differently from IL-13, which cooperate to induce optimal gene expression.

Characterisation of effector mechanisms at the host:parasite interface during the immune response to tissue-dwelling intestinal nematode parasites

The protective immune response that develops following infection with many tissue-dwelling intestinal nematode parasites is characterised by elevations in IL-4 and IL-13 and increased numbers of CD4+ T cells, granulocytes and macrophages. These cells accumulate at the site of infection and in many cases can mediate resistance to these large multicellular pathogens. Recent studies suggest novel potential mechanisms mediated by these immune cell populations through their differential activation and ability to stimulate production of novel effector molecules. These newly discovered protective mechanisms may provide novel strategies to develop immunotherapies and vaccines against this group of pathogens. In this review, we will examine recent studies elucidating mechanisms of host protection against three widely-used experimental murine models of tissue-dwelling intestinal nematode parasites: Heligmosomoides polygyrus, Trichuris muris and Trichinella spiralis.

Induction of Ym1/2 in mouse bone marrow-derived mast cells by IL-4 and identification of Ym1/2 in connective tissue type-like mast cells derived from bone marrow cells cultured with IL-4 and stem cell factor

Mast cells play an important role in allergic inflammation by releasing various bioactive mediators. The function of mast cells is enhanced by various stimuli, partly due to the induction of specific genes and their products. Although many inducible genes have been identified, a significant number of genes remain to be identified. Therefore, this study used PCR-selected cDNA subtraction to establish the profile of induced genes in the connective tissue (CT) type-like mast cells derived from bone marrow cells cultured in the presence of IL-4 and stem cell factor. Two hundred and fifty cDNA clones were obtained from the CT type-like mast cells by PCR-selected cDNA subtraction. Among them, Ym1/2, a chitinase-like protein, is one of the most abundantly induced genes. Ym1 is produced by activated macrophages in a parasitic infection, whereas its isotype, Ym2, is highly upregulated in allergic lung disease. In order to differentiate which isotype is expressed in bone marrow cells, specific primers for bone marrow-derived mast cells (BMMC), and CT type-like mast cells were used for RT-PCR. The results showed that Ym1 was constitutively expressed in bone marrow cells and gradually decreased in the presence of IL-3, whereas Ym2 was induced only in the presence of IL-4. CT type-like mast cells from bone marrow cells expressed Ym1 throughout the culture period and Ym2 was induced only by the addition of IL-4 into BMMC, indicating that IL-4 is essential for the expression of Ym1/2 genes.

New weapons in the war on worms: identification of putative mechanisms of immune-mediated expulsion of gastrointestinal nematodes

Parasitic nematode infections of humans and livestock continue to impose a significant public health and economic burden worldwide. Murine models of intestinal nematode infection have proved to be relevant and tractable systems to define the cellular and molecular basis of how the host immune system regulates resistance and susceptibility to infection. While susceptibility to chronic infection is propagated by T helper cell type 1 cytokine responses (characterised by production of IL-12, IL-18 and interferon-gamma), immunity to intestinal-dwelling adult nematode worms is critically dependent on a type 2 cytokine response (controlled by CD4+T helper type 2 cells that secrete the cytokines IL-4, IL-5, IL-9 and IL-13). However, the immune effector mechanisms elicited by type 2 cytokines in the gut microenvironment that precipitate worm expulsion have remained elusive. This review focuses on new studies that implicate host intestinal epithelial cells as one of the dominant immune effector cells against this group of pathogens. Specifically, three recently identified type 2 cytokine-dependent pathways that could offer insights into the mechanisms of expulsion of parasitic nematodes will be discussed: (i) the intelectins, a new family of galactose-binding lectins implicated in innate immunity, (ii) the resistin-like molecules, a family of small cysteine-rich proteins expressed by multiple cell types, and (iii) cytokine regulation of intestinal epithelial cell turnover. Identifying how the mammalian immune response fights gastrointestinal nematode infections is providing new insights into host protective immunity. Harnessing these discoveries, coupled with identifying what the targets of these responses are within parasitic nematodes, offers promise in the design of a new generation of anti-parasitic drugs and vaccines.

Influence of Toxocara canis infection during pregnancy on offspring resistance towards re-infection

The impact of Toxocara canis infection of Balb/c mice mothers on the future immune response of their offspring towards reinfection with the same parasite was studied. Two groups of offspring, the first originating from the mothers infected with a single dose of 1000 Toxocara canis eggs and the second from non-infected mothers, were both challenged with 500 T. canis eggs per animal at 6 weeks of age. The proportions of spleen CD4+ and CD8+ T lymphocytes, the level of serum cytokines IFN-gamma and IL-5, eosinophilia in peripheral blood, the production of specific antibodies and the number of migrating larvae were monitored. In both groups of offspring, the challenge infection resulted in an increase in CD4+ T-cell subtype in comparison with the non-infected healthy control, although after an initial decline a subsequent increase in CD8+ was observed. The immunoregulation index (CD4+/CD8+) was lower in the group of mice originating from infected mothers throughout the whole experiment compared to the offspring of non-infected mothers as well as in healthy control mice of the same age. In the offspring of infected mothers mainly, a reduced production of IFN-gamma and of IL-5, suppressed eosinophilia and a higher level of protective antibodies was detected, compared to the control second group, in which the INF-gamma concentration significantly increased after day 42 p.i. In the first group of offspring before challenge, 12.7 +/- 2.5 larvae in the brains and 32 +/- 2.1 larvae in the muscles transmitted from the infected mothers were detected. There was a significant reduction in larval recovery from brain on days 42 and 49 p.i. (56.7 and 56.8%, respectively), while from muscles in the same time there was a reduction of 46.7 and 39%, respectively, compared to the offspring of non-infected mothers. These results indicate a significant protective memory of immune mechanisms against T. canis induced in offspring of Toxocara-infected mother mice.

Expression of the full-length form of gp2 of equine herpesvirus 1 (EHV-1) completely restores respiratory virulence to the attenuated EHV-1 strain KyA in CBA mice

Wild-type equine herpesvirus 1 (EHV-1) strains express a large (250-kDa) glycoprotein, gp2, that is encoded by EUs4 (gene 71) located within the unique short region of the genome. DNA sequence analysis revealed that EUs4 of the pathogenic EHV-1 strain RacL11 is an open reading frame of 2,376 bp that encodes a protein of 791 amino acids. The attenuated EHV-1 vaccine strain KyA harbors an in-frame deletion of 1,242 bp from bp 222 to 1461 and expresses a truncated gp2 of 383 amino acids. To determine the relative contribution of gp2 to EHV-1 pathogenesis, we compared the course of respiratory infection of CBA mice infected with either wild-type RacL11, attenuated KyA, or a recombinant KyA that expresses the full-length gp2 protein (KyARgp2F). Mice infected with KyA lost a negligible amount of body weight (0.18% total weight loss) on day 1 postinfection and regained weight thereafter, whereas mice infected with KyARgp2F or RacL11 steadily lost weight beginning on day 1 and experienced a 20 and 18% loss in body weight, respectively, by day 3. Immunohistochemical and flow cytometric analyses revealed higher numbers of T and B lymphocytes and an extensive consolidation consisting of large numbers of Mac-1-positive cells in the lungs of animals infected with KyARgp2F compared to animals infected with KyA. RNase protection analyses revealed increased expression of numerous cytokines and chemokines, including interleukin-1beta (IL-1beta), IL-6, tumor necrosis factor alpha, macrophage inflammatory protein 1alpha (MIP-1alpha), MIP-1beta, MIP-2, interferon gamma-inducible protein, monocyte chemotactic protein 1, and T-cell activation gene 3 at 12 h postinfection with KyARgp2F. Three independent DNA array experiments confirmed these results and showed a 2- to 13-fold increase in the expression of 31 inflammatory genes at 8 and 12 h postinfection with KyARgp2F compared to infection with KyA. Taken together, the results indicate that expression of full-length gp2 is sufficient to restore full respiratory virulence to the attenuated KyA strain and raise caution concerning the inclusion of full-length gp2 in the development of EHV-1 vaccines.

Chitinase and Fizz family members are a generalized feature of nematode infection with selective upregulation of Ym1 and Fizz1 by antigen-presenting cells

Ym1 and Fizz1 are secreted proteins that have been identified in a variety of Th2-mediated inflammatory settings. We originally found Ym1 and Fizz1 as highly expressed macrophage genes in a Brugia malayi infection model. Here, we show that their expression is a generalized feature of nematode infection and that they are induced at the site of infection with both the tissue nematode Litomosoides sigmodontis and the gastrointestinal nematode Nippostrongylus brasiliensis. At the sites of infection with N. brasiliensis, we also observed induction of other chitinase and Fizz family members (ChaFFs): acidic mammalian chitinase (AMCase) and Fizz2. The high expression of both Ym1 and AMCase in the lungs of infected mice suggests that abundant chitinase production is an important feature of Th2 immune responses in the lung. In addition to expression of ChaFFs in the tissues, Ym1 and Fizz1 expression was observed in the lymph nodes. Expression both in vitro and in vivo was restricted to antigen-presenting cells, with the highest expression in B cells and macrophages. ChaFFs may therefore be important effector or wound-repair molecules at the site of nematode infection, with potential regulatory roles for Ym1 and Fizz1 in the draining lymph nodes.

Macrophages in chronic type 2 inflammation have a novel phenotype characterized by the abundant expression of Ym1 and Fizz1 that can be partly replicated in vitro

Using a murine model of nematode infection, we have discovered macrophages that display a novel phenotype that may be characteristic of macrophages in chronic type 2 inflammation. These nematode-elicited macrophages (NeMphi) are characterized by two unique features: the ability to actively suppress proliferation of a broad range of cell types and the high level expression of two novel macrophage genes, Ym1 and Fizz1. NeMphi also show some similarities with in vitro-derived 'alternatively activated macrophages' such as the downregulation of inflammatory cytokines. We therefore investigated how much of the phenotype discovered in vivo could be replicated by activation with Th2 cytokines in vitro. Fizz1 and Ym1 were upregulated by IL-4 and IL-13 in vitro but at a considerably lower level than in NeMphi. In vitro treatment with IL-4 could also partly replicate the ability of NeMphi to block cellular proliferation. As well as the quantitative differences in gene expression and suppressive phenotype, we also observed phenotypic differences in the cell morphology between macrophages activated in vivo and in vitro. Although this study illustrated that macrophages activated in chronic inflammation have distinct features that cannot be readily reproduced in vitro it also demonstrated that some features of the complex NeMphi phenotype can be replicated by treatment of cultured macrophages with Th2 cytokines. In future, we hope to use in vitro analysis to help define the pathways that lead to this distinctive in vivo macrophage phenotype.

Expression of the Ym2 lectin-binding protein is dependent on interleukin (IL)-4 and IL-13 signal transduction: identification of a novel allergy-associated protein

Asthma pathophysiology is intimately regulated by CD4(+) Th2 lymphocytes and the cytokines interleukin (IL)-4 and IL-13. However, the mechanisms by which these cytokines promote disease have not been fully elucidated. In order to identify novel molecular mediators of allergy, a comparison was made of the bronchoalveolar lavage, which demonstrated that the Ym2 protein was abundantly up-regulated in the lung during the development of allergy. Low levels of the Ym1 isomer were also detected. Importantly, neither Ym1 nor Ym2 has been characterized previously in the context of allergic pulmonary inflammation. Western immunoblot showed that enhanced expression of these proteins was dependent on CD4(+) T cells and IL-4 or IL-13 signaling via the IL-4Ralpha subunit. In addition, intratracheal instillation of IL-13 into naive mice was sufficient to induce expression. Ym1 is homologous to eosinophil chemotactic factor L. However, only weak eosinophil chemotaxis was observed in response to Ym protein in both in vitro and in vivo assays. By contrast, the homology of Ym1 and Ym2 to proteins associated with tissue remodeling, together with the previous findings that Ym1 is homologous to chitinase and binds heparin sulfate and GlcN oligomers (chitobiose, chitotriose, and chitotetraose), strongly suggests these proteins play an important role in airway wall remodeling in the allergic lung.

A Brugia malayi homolog of macrophage migration inhibitory factor reveals an important link between macrophages and eosinophil recruitment during nematode infection

Infections with the helminth parasite Brugia malayi share many key features with Th2-mediated allergic diseases, including recruitment of eosinophils. We have investigated the dynamics of inflammatory cell recruitment under type 2 cytokine conditions in mice infected with B. malayi. Among the cells recruited to the site of infection is a novel population of "alternatively activated" macrophages that ablate cell proliferation and enhance Th2 differentiation. By profiling gene expression in this macrophage population, we found a dramatic up-regulation of a recently described eosinophil chemotactic factor, eosinophil chemotactic factor-L/Ym1, representing over 9% of clones randomly selected from a cDNA library. Because B. malayi is known to secrete homologs (Bm macrophage migration inhibitory factor (MIF)-1 and -2) of the human cytokine MIF, we chose to investigate the role this cytokine mimic may play in the development of the novel macrophage phenotype observed during infection. Strikingly, administration of soluble recombinant Bm-MIF-1 was able to reproduce the effects of live parasites, leading both to the up-regulation of Ym1 by macrophages and a marked recruitment of eosinophils in vivo. Because activity of Bm-MIF-1 is dependent upon an amino-terminal proline, this residue was mutated to glycine; the resultant recombinant (Bm-MIF-1G) was unable to induce Ym1 transcription in macrophages or to mediate the recruitment of eosinophils. These data suggest that macrophages may provide a crucial link between helminth parasites, their active cytokine mimics, and the recruitment of eosinophils in infection.

A macrophage protein, Ym1, transiently expressed during inflammation is a novel mammalian lectin

Oral infections of mice with Trichinella spiralis induce activation of peritoneal exudate cells to transiently express and secrete a crystallizable protein Ym1. Purification of Ym1 to homogeneity was achieved. It is a single chain polypeptide (45 kDa) with a strong tendency to crystallize at its isoelectric point (pI 5.7). Co-expression of Ym1 with Mac-1 and scavenger receptor pinpoints macrophages as its main producer. Protein microsequencing data provide information required for full-length cDNA cloning from libraries constructed from activated peritoneal exudate cells. A single open reading frame of 398 amino acids with a leader peptide (21 residues) typical of secretory protein was deduced and later deposited in GenBank (accession number M94584) in 1992. By means of surface plasmon resonance analyses, Ym1 has been shown to exhibit binding specificity to saccharides with a free amine group, such as GlcN, GalN, or GlcN polymers, but it failed to bind to other saccharides. The interaction is pH-dependent but Ca2+ and Mg2+ ion-independent. The binding avidity of Ym1 to GlcN oligosaccharides was enhanced by more than 1000-fold due to the clustering effect. Specific binding of Ym1 to heparin suggests that heparin/heparan sulfate may be its physiological ligand in vivo during inflammation and/or tissue remodeling. Although it shares approximately 30% homology with microbial chitinases, no chitinase activity was found associated with Ym1. Genomic Southern blot analyses suggest that Ym1 may represent a member of a novel lectin gene family.

Biochemical characterization of endogenously formed eosinophilic crystals in the lungs of mice

Crystals seldom form spontaneously within tissues of mammals, except in the urinary tract or in association with eosinophil-rich diseases in humans (Charcot-Leyden crystals). Endogenously formed eosinophilic crystals have been reported in respiratory tract and other tissues of several strains of mice, but the biochemical characterization of these crystals has not been reported. In this study, eosinophilic crystal formation was examined in homozygous C57BL/6J viable motheaten mice, lung-specific surfactant apoprotein C promoter/soluble human tumor necrosis factor p75 receptor type II fusion protein transgenic mice (C57BL/6NTac x Sv/129), and CD40L-deficient mice with spontaneous Pneumocystis carinii infection. In viable motheaten but not wild type mice, rapidly developing crystals represented a major feature of the fatal lung injury induced by macrophage dysregulation. Conversely, eosinophilic crystals did not form until 4-8 months of age in transgenic and CD40L-deficient mice and were present in 10-30% of age-matched wild type controls. Mass spectrometry analysis of proteins from bronchoalveolar lavage fluid identified the crystals as Ym1, sometimes referred to as T-lymphocyte-derived eosinophil chemotactic factor. The Ym1 sequence was homologous to chitinase, and enzymatic assays indicated a 3-5-fold increase in chitinase activity compared with control mice. Intracellular and extracellular crystals associated with epithelial damage suggested that the crystals may contribute to lung inflammation through mechanical damage and enzymatic degradation.

Identification of a novel eosinophil chemotactic cytokine (ECF-L) as a chitinase family protein

A novel eosinophil chemotactic cytokine (ECF-L) was purified from the culture supernatant of splenocytes of mice by a combination of anion-exchange chromatography, Procion red-agarose affinity chromatography, size exclusion high performance liquid chromatography (HPLC), and reverse phase HPLC. The NH(2)-terminal amino acid sequence was determined by direct protein sequencing. An ECF-L cDNA clone of 1,506 nucleotides was isolated from a cDNA library, and the nucleotide sequence predicted a mature protein of 397 amino acids. A recombinant ECF-L showed a level of eosinophil chemotactic activity comparable with that of natural ECF-L, and the activity was inhibited by a monoclonal antibody to ECF-L. ECF-L also attracted T lymphocytes and bone marrow polymorphonuclear leukocytes in vitro, whereas it caused selective extravasation of eosinophils in vivo. ECF-L mRNA was highly expressed in spleen, bone marrow, lung, and heart. A comprehensive GenBank data base search revealed that ECF-L is a chitinase family protein. ECF-L retains those amino acids highly conserved among chitinase family proteins, but Asp and Glu residues essential for the proton donation in hydrolysis were replaced by Asn and Gln, respectively. Although ECF-L contains a consensus CXC sequence near the NH(2) terminus akin to chemokine family proteins, the rest of ECF-L shows poor homology with chemokines.