Inhibition of neutrophil oxidative metabolism by trichinellosis patient sera. Parasite origin or host induction?

Modulatory Effect of Beneficial Enterococci and Their Enterocins on the Blood Phagocytes in Murine Experimental Trichinellosis

Bacteriocins (enterocins) represent a new therapeutic strategy in various intestinal and non-intestinal infections. In antiparasitic defence, an oxidative inflammation of phagocytes is effective in destroying new-born Trichinella spiralis larvae. The strains Enterococcus faecium CCM8558 and E. durans ED26E/7 and their enterocins, enterocin M and a durancin-like enterocin, respectively, were administered daily, and mice were then infected with T. spiralis larvae on the seventh day of treatment. Phagotest and Bursttest kits were used to detect the phagocytosis and respiratory burst in blood leukocytes. T. spiralis infection inhibited phagocytosis from day 11 post-infection (dpi) during the migration of new-born larvae into the muscles. E. faecium CCM8558, E. durans ED26E/7, and the durancin-like enterocin increased phagocytic activity from day 11 dpi. Both strains and their enterocins (enterocin M and durancin-like) stimulated the ingestion capability of phagocytes from 18 to 32 dpi. Enterococci/enterocins therapy prevented a reduction in cells with respiratory burst caused by T. spiralis infection from 11 dpi. The enzymatic activity of phagocytes was stimulated on 18 and 25 dpi, particularly by E. faecium CCM8558 and enterocin M. Enterocin M and the durancin-like enterocin were as effective in stimulating phagocytosis as the bacterial strains that produce them. The stimulation of phagocytosis could contribute to decreased larval migration and reduced parasite burden in the host.

Effect of probiotic bacteria on phagocytosis and respiratory burst activity of blood polymorphonuclear leukocytes (PMNL) in mice infected with Trichinella spiralis

This study focusses on the effect of probiotic (bacteriocinogenic) strains on parasite infection and innate immunity - phagocytosis and oxidative burst of blood monocytes and polymorphonuclear leukocytes (PMNL) in mice infected with Trichinella spiralis. Bacteriocinogenic and probiotic strains of different origin (Enterococcus faecium AL41=CCM8558, Enterococcus durans ED26E/7, Lactobacillus fermentum AD1=CCM7421, Lactobacillus plantarum 17L/1) were administered daily in dose of 10⁹CFU/ml in 100μl and mice were infected with 400 larvae of T. spiralis on 7th day of treatment. Phagocytic activity of blood leukocytes was inhibited at week 3 and 4 post infection (p.i.), i.e. in the time of massive muscle invasion with larvae T. spiralis. Administration of bacterial strains to mice prior to T. spiralis infection elevated and prolonged phagocytic activity of blood leukocytes and their ingestion capability from week 1 to 3 of the infection and the phagocytosis was inhibited only at week 4 p.i. The highest stimulative effect on phagocytosis was induced by strains E. durans ED26E/7, L. fermentum AD1=CCM7421, and L. plantarum 17L/1. The percentage of cells with respiratory burst and their enzymatic activity was increased after T. spiralis infection with the exception of week 3 p.i. In contrast, in all mice treated with bacterial strains the enzymatic stimulation was observed after the infection, with the highest intensity caused by strains E. durans ED26E/7, L. fermentum AD1=CCM7421 and L. plantarum 17L/1. The administration of probiotic strains stimulated phagocytosis and respiratory burst of blood PMNL that could contribute to a decreased larval migration and a destruction of muscle larvae and then reduced parasite burden in the host. The protective effect against T. spiralis infection was induced by all strains, but the highest reduction was recorded by E. faecium AL41=CCM8558.

Effects of protoscoleces and AgB from Echinococcus granulosus on human neutrophils: possible implications on the parasite's immune evasion mechanisms

The factors affecting the innate susceptibility to Echinococcus granulosus infections are largely unknown. We assessed the interaction of healthy human neutrophils with protoscoleces (PSC) and antigen B (AgB) of E. granulosus by analysis of CD11b upregulation and H(2)O(2) production by flow cytometry. PSC induced neutrophil activation, but their viability was not affected. In contrast, no effects were observed with AgB in both assays. Neutrophil-enriched fractions were also incubated with PSC or AgB, and interleukin 8 (IL-8) production was measured by ELISA. Significant increment in IL-8 production was detected only in supernatants from neutrophil-enriched fractions cultured with PSC. The possible effect of a prior incubation with AgB on the phorbol myristate acetate-induced activation was also evaluated. No changes were observed in CD11b expression, but the H(2)O(2) production was significantly reduced in platelet-activating factor (PAF)-primed neutrophils. These results suggest a possible AgB-mediated mechanism of evasion of the host immune response, which would operate upon events of spillage of the fertile hydatid cyst content.

Screening of an Echinococcus granulosus cDNA library with IgG4 from patients with cystic echinococcosis identifies a new tegumental protein involved in the immune escape

The worldwide problem of chronic Echinococcus granulosus disease calls for new parasite-derived immunomodulatory molecules. By screening an E. granulosus cDNA library with IgG4 from patients with active cystic echinococcosis, we identified a cDNA that encodes a predicted partial protein that immunofluorescence studies localized in the protoscolex tegument and on the germinal layer of cyst wall. We named this protein EgTeg because the 105 amino acid sequence scored highest against a family of Schistosoma tegumental proteins. Evaluating the role of EgTeg in the human early inflammatory response we found that EgTeg significantly inhibited polymorphonuclear cell (PMN) chemotaxis. Cytometric analysis of intracellular cytokines disclosed a significantly higher percentage of cells producing IL-4 than IFN-gamma (P = 0.001, Student's t-test) in T lymphocytes from patients with cystic echinococcosis stimulated with EgTeg. EgTeg induced weak Th1-dependent proliferation in 42% of patients' peripheral blood mononuclear cells. In immunoblotting (IB) analysis of total IgG and IgG subclass responses to EgTeg in patients with cystic echinococcosis, patients with other parasitoses, patients with cystic lesions and healthy controls, total IgG specific to EgTeg yielded high sensitivity (73%) but low specificity (44%) precluding its use in immunodiagnosis. Conversely, IgG4 specific to EgTeg gave acceptable sensitivity (65%) and high specificity (89%) suggesting its use in immunodiagnosis to confirm ultrasound documented cysts suggestive of E. granulosus. Because the new tegumental antigen EgTeg inhibits chemotaxis, induces IL-4-positive T lymphocytes and noncomplement fixing antibodies (IgG4) it is an immunomodulatory molecule associated with chronic infection.

Early response of guinea-pig lungs to Trichinella spiralis infection

In order to assess immunological response, induced in guinea-pig lungs by Trichinella spiralis, cellular infiltration into pulmonary alveolar space and production of O(2)(-) and NO in alveolar macrophages obtained from bronchoalveolar lavage fluid (BALF), as well as accumulation of nitric oxide (NO) metabolites in BALF and serum, were evaluated during the early period of primary T. spiralis infection (from 4th to 8th and on 14th day after oral administration of larvae) and on 6th day after secondary infection. Primary infection caused increased infiltration of lymphocytes, macrophages, neutrophils and eosinophils, while secondary infection resulted in raised lymphocyte and eosinophil numbers. In spite of marked cellular infiltration of alveolar space, only very limited activation of effector cells, pointing to a suppressed innate response, was apparent, as (i) BALF supernatant phospholipid/protein concentration ratio, and lung levels of phospholipid peroxidation markers, conjugated dienes and malondialdehyde, did not change during 7 days following infection; (ii) primary, but not secondary, infection caused only a transient increase of superoxide anion production by alveolar macrophages; (iii) despite expression of inducible nitric oxide synthase in macrophages of control, infected and BCG-treated animals, and of interferon (IFN)-gamma-like activity in sera of infected animals, macrophage nitric oxide production was not affected by infection, even after additional stimulation in vitro (lipopolisaccharide + hrIFN-gamma) or in vivo (BCG or secondary T. spiralis infection); and (iv) increased nitrate concentrations were found in BALF supernatant and serum, but not in lung homogenates, of infected animals.

Modulation of human immune response by Echinococcus granulosus antigen B and its possible role in evading host defenses

By directly suppressing the function of certain immune cell subsets and by stimulating other cell populations related to immunopathology, parasite-derived substances play an important role in the chronic establishment of parasitic disease. Our objective was twofold: (i) to investigate further the role of Echinococcus granulosus antigen B (AgB) in the human early inflammatory response by determining its effect on polymorphonuclear cell (PMN) random migration, chemotaxis, and oxidative metabolism and (ii) to determine its action in acquired immunity by evaluating AgB and sheep hydatid fluid (SHF)-driven Th1 (gamma interferon [IFN-gamma] and interleukin 12 [IL-12]) and Th2 (IL-4 and IL-13) cytokine production by peripheral blood mononuclear cells (PBMC) from 40 patients who had cured or stable or progressive cystic echinococcosis. AgB significantly inhibited PMN recruitment but left their random migration and oxidative metabolism unchanged. Patients' PBMC stimulated with AgB produced IL-4 and IL-13 but did not produce IL-12. They also produced significantly lower IFN-gamma concentrations than did PBMC stimulated with SHF (P = 10(-5)). AgB skewed the Th1/Th2 cytokine ratios towards a preferentially immunopathology-associated Th2 polarization, predominantly in patients with progressive disease. AgB-stimulated patients' PBMC also proliferated less than SHF-stimulated PBMC (P = 9 x 10(-3)). In vitro Th2 cytokine production was reflected in vivo by elevated specific immunoglobulin E (IgE) and IgG4 antibodies binding to AgB. These findings confirm that AgB plays a role in the escape from early immunity by inhibiting PMN chemotaxis. They also add new information on the host-parasite relationship, suggesting that AgB exploits the activation of T helper cells by eliciting a nonprotective Th2 cell response.

Secretion of IL-12 by murine macrophages activated by immunoglobulin receptor-mediated internalization of the surface coat of Trichinella spiralis larvae

Trichinella spiralis larvae incubated with a rabbit antiserum raised against the larval surface coat bound murine macrophages to the parasite surface. Cell binding was not observed without the antisurface coat serum, or with incubation of larvae in normal rabbit serum, or with antibodies to keyhole limpet haemocyanin which identify a cryptic T. spiralis larval antigen. Cell adherence to the larval surface was lost by treatment of the cells with the lysosomotropic drug primaquine, implicating a receptor-mediated mechanism. Cells adhering to the parasite surface internalized parasite surface coat material, which was subsequently concentrated into endosomes. Culture supernatants from these cells contained enhanced levels of IL-12. Thus, the initial Th1 response to T. spiralis infection may be explained by these data.

Defence against the immune barrage: helminth survival strategies

Parasites have generated a range of countermeasures against the host immune system which allows their survival long enough for reproduction to occur. Parasite subsistence is enhanced by evasion of the immune response utilizing mechanisms such as antigenic variation of exposed immunogenic proteins, shedding of surface proteins which are the target of an immune response, and protease production to neutralise specific anti-parasite immune components. Recent advances in the fields of immunology and parasitology have highlighted a range of mechanisms by which the parasite actively modulates the immune response to allow survival. Parasite factors can directly suppress the function of certain subsets of immune cells as well as stimulating other cell populations which have suppressive activity. Strategies such as the skewing of the type 1-type 2 cytokine profile to that of a less appropriate response, and the mimicry of host immune regulatory proteins are becoming more widely acknowledged as means by which helminths enhance their survival. An illustration of the extent by which parasites can exploit host immune components is emphasized by the use of host cytokines as parasite growth factors. This review will examine some of the strategies developed by helminths which enables them not only to survive in the host, but also to prosper.