Strongyloides ratti infection induces transient nematode-specific Th2 response and reciprocal suppression of IFN-gamma production in mice

Over one-third of the world population is infected with parasitic helminths, Strongyloides ssp. accounting for approximately 30-100 million infected people. In this study, we employ the experimental system of murine Strongyloides ratti infection to investigate the interaction of this pathogenic nematode with its mammalian host. We provide a comprehensive kinetic description of the immune response to S. ratti infection that was reflected by induction of antigen-specific IgM and IgG1, mast cell activation and a Th2-like cytokine response. T cells derived from infected mice displayed an increased IL-3, IL-4, IL-5, IL-13 and IL-10 response to CD3-engagement in comparison with T cells derived from naïve mice. The IFN-gamma response to CD3-engagement that was well detectable in T cells derived from naïve mice, however, was suppressed in T cells derived from infected mice. Both, the induction of the S. ratti-specific Th2 response and the suppression of pro-inflammatory cytokines were transient and observed in strict correlation to the course of infection and the number of infective larvae used. Finally, comparing artificial infections induced by subcutaneous injection of larvae to natural infections, we observed similar antigen-specific T cell responses although the natural infection led to a significantly lower worm burden.

Cutaneous pathology in onchocerciasis associated with pronounced systemic T-helper 2-type responses to Onchocerca volvulus

BACKGROUND

Of 18 million people world-wide who are infested with the tissue nematode Onchocerca volvulus, more than 30% are considered to have skin lesions, the pathomechanisms of which are poorly understood.

OBJECTIVES

To relate skin changes associated with onchocerciasis to parasitological findings and systemic cellular immune responses.

METHODS

In the course of a genetic study, 691 members of 241 families exposed to hyperendemic O. volvulus transmission and free of other filarial or schistosomal infestations were studied clinically, by counting palpable Onchocerca nodules and skin microfilariae, by measuring peripheral blood cell (PBC) counts and total serum IgE, and by determining PBC in vitro proliferation and cytokine secretion in response to O. volvulus antigen.

RESULTS

Of 691 individuals studied, 219 presented with onchocerciasis-associated skin changes. The groups of individuals with and without skin lesions neither differed in prevalences nor in average numbers of microfilariae. Compared with individuals without skin lesions, pronounced systemic T-helper (Th) 2-type responses were found with a trend of increasing intensity in the order of depigmentation, papular dermatitis, atrophy and lichenified dermatitis. Differences between the groups were most pronounced for serum IgE, less so for eosinophilia, and relatively weak for PBC proliferation and interleukin-5 secretion.

CONCLUSIONS

Skin lesions in onchocerciasis are associated with a spectrum of increasing generalized Th2-type responses ranging from low reactivities in cases of depigmentation alone to strong reactivities in cases of lichenification.

Renal dysfunction in children with uncomplicated, Plasmodium falciparum malaria in Tamale, Ghana

In a study performed in Tamale, in the Northern region of Ghana, cystatin C, a new and sensitive indicator of the glomerular filtration rate (GFR), was used to estimate the frequency of renal dysfunction in 78 children with uncomplicated, Plasmodium falciparum malaria. The excretion in urine of albumin, immunoglobulin G and alpha1-microglobulin was also investigated. Plasma concentrations of cystatin C were found to be elevated in 17% of the children, indicating subclinical impairment of renal function. As most (85%) of the children had glomerular as well as tubular patterns of proteinuria, it appears that both glomerulonephritis and damage to tubular cells often occur in P. falciparum malaria.

[Bacterial symbionts (Wolbachia) of filarial nematodes: implications for the treatment and pathology of filariasis]

Filarial nematodes harbour intracellular, Gram-negative bacteria belonging to the genus Wolbachia. These bacteria have been observed in various species of filariae, including the main filariasis agents of humans and animals. It has been suggested that Wolbachia could play an important role in the biology of filarial nematodes and could be implicated in the pathogenesis of filarial diseases. Wolbachia could thus represent a target for the control of filariasis and key to the understanding of these diseases. Indeed, in various species of filariae, tetracycline treatments have been shown both to reduce/eliminate the Wolbachia population and to determine detrimental effects on the nematodes. In addition, proteins of Wolbachia have been shown to determine specific IgG responses in animals infected by filariae and some Wolbachia molecules (e.g. LPS) have been shown to stimulate innate-immunity responses (e.g. production of cytokines such as IL1, IL6, IL10, TNF-alpha and IFN-gamma by macrophages).

Structural analysis and antibody response to the extracellular glutathione S-transferases from Onchocerca volvulus

Onchocerca volvulus is a human pathogenic filarial parasite which, like other parasitic nematodes, is capable of surviving in an immunologically competent host by employing a variety of immune evasion strategies and defense mechanisms including the detoxification and repair mechanisms of the glutathione S-transferases (GSTs). In this study we analyzed the glycosylation pattern and the immunological properties of extracellular O. volvulus GST1a and -1b (OvGST1a and -1b). The enzymes differ in only 10 amino acids, and both are glycoproteins that have cleavable signal peptides and unusual N-terminal extensions. These characteristics have not been described for other GSTs so far. Mass spectrometry analyses indicate that both enzymes carry high-mannose type oligosaccharides on at least four glycosylation sites. Glycosylation sites 1 to 3 of OvGST1a (OvGST1b sites 2 to 4) are occupied by truncated N-glycans (Man(2)GlcNAc2 to Man(5)GlcNAc(2)), and N glycosylation site 4 of OvGST1a (OvGST1b site 5) carries Man(5)GlcNAc2 to Man(9)GlcNAc(2). To analyze the capacity of these secretory GSTs to stimulate host immune responses, we studied the antibody responses of onchocerciasis patients against the native affinity-purified OvGST1a and -1b. By enzyme-linked immunosorbent assay we showed that OvGST1a and -1b are immunodominant antigens, with less than 7% nonresponder patients. A direct comparison of the antibody responses to the glycosylated and deglycosylated forms demonstrates the high immunogenicity of the N-glycans. Analyses of the antibody responses to the unusual N-terminal extension show an enhanced recognition of this portion by patients as opposed to recognition of the recombinant protein without extension.

Modulation of human T cell responses and macrophage functions by onchocystatin, a secreted protein of the filarial nematode Onchocerca volvulus

Immune responses of individuals infected with filarial nematodes are characterized by a marked cellular hyporesponsiveness and a shift of the cytokine balance toward a Th2/Th3 response. This modulation of cellular immune responses is considered as an important mechanism to avoid inflammatory immune responses that could eliminate the parasites. We investigated the immunomodulatory potential of a secreted cysteine protease inhibitor (onchocystatin) of the human pathogenic filaria Onchocerca volvulus. Recombinant onchocystatin (rOv17), a biologically active cysteine protease inhibitor that inhibited among others the human cysteine proteases cathepsins L and S, suppressed the polyclonally stimulated and the Ag-driven proliferation of human PBMC. Stimulated as well as unstimulated PBMC in the presence of rOv17 produced significantly more IL-10, which was paralleled in some situations by a decrease of IL-12p40 and preceded by an increase of TNF-alpha. At the same time, rOv17 reduced the expression of HLA-DR proteins and of the costimulatory molecule CD86 on human monocytes. Neutralization of IL-10 by specific Abs restored the expression of HLA-DR and CD86, whereas the proliferative block remained unaffected. Depletion of monocytes from the PBMC reversed the rOv17-induced cellular hyporeactivity, indicating monocytes to be the target cells of immunomodulation. Therefore, onchocystatin has the potential to contribute to a state of cellular hyporesponsiveness and is a possible pathogenicity factor essential for the persistence of O. volvulus within its human host.

Lack of interferon-γ confers impaired neutrophil granulocyte function and imparts prolonged survival of adult filarial worms in murine filariasis

We investigated the role of IFN-gamma in host defense during murine filariasis. Using the fully permissive infection of BALB/c mice with the rodent filaria Litomosoides sigmodontis, we show that interferon (IFN)-gamma is essential for encapsulation of adult filarial worms in inflammatory nodules and for normal worm clearance. IFN-gamma knockout (KO) mice had only one third of the nodules of wild-type mice but displayed a more than twofold increase in worm burden and increased microfilaremia. Neutrophil granulocytes, but not macrophages or eosinophils, appear to directly control worm load and nodule formation. Neutrophils, which we showed earlier to be essential for the encapsulation process in the thoracic cavity, where the worms reside, were diminished at this location in IFN-gamma KO compared to wild-type mice; they also displayed strongly reduced chemotactic and phagocytic activity compared to neutrophils of controls. This argues for a distinct defect in neutrophil activation accounting for the low formation of inflammatory nodules. Tumor necrosis factor-alpha, a major neutrophil-activating cytokine expressed by macrophages in the thoracic cavity around the worms, was highly induced in wild-type but absent in KO mice. Diminished activation of neutrophils seems to be a general hallmark of IFN-gamma KO mice, since neutrophils from uninfected KO mice also showed a reduction in chemotactic and phagocytic activity when induced by casein. In conclusion, these data are the first to define an IFN-gamma-dependent immune effector mechanism in murine filarial infection, i.e. neutrophil-mediated control of the adult worm load.

Localization of T and B cell stimulating domains of the immunodominant 33-kDa protein of Onchocerca volvulus (Ov33)

The localization of T and B cell epitopes on a well characterized 33-kDa protein of the filarial nematode Onchocerca volvulus (Ov33) was studied using peripheral blood mononuclear cells (PBMC) and sera from a total of 52 onchocerciasis patients with the generalized form of infection. A proportion of the PBMC samples proliferated in response to recombinant Ov33-GST fusion protein and to fusion free Ov33-6xHis. Proliferative responses of patient PBMC to seven truncated Ov33-6xHis polypeptides and to three synthetic peptides revealed at least one major and two minor T cell epitopes in the protein. The dominant T cell stimulating domain was localized between amino acids 113 and 143. ELISA studies with the Ov33-GST fusion protein revealed that patient sera contained Ov33-specific IgG1, IgG4, IgE, and IgM antibodies. Analysis of the IgG4 response with 10 truncated Ov33 polypeptides identified four B cell stimulating domains in the N-terminal, central, and C-terminal region of the molecule. The B cell domain recognized by the majority of sera was localized between amino acids 113 and 143. The data indicate that this region of the protein is the major T and B cell stimulating domain of Ov33 and might be relevant for vaccine development and for improved immunodiagnosis of onchocerciasis.

Differences in cytokine responses to Onchocerca volvulus extract and recombinant Ov33 and OvL3-1 proteins in exposed subjects with various parasitologic and clinical states

Subjects with generalized onchocerciasis (GEN), with the sowdah form, and with exposure but without onchocerciasis (endemic normal/putatively immune; EN/PI) were studied for cytokine responses to Onchocerca volvulus extract (OvAg) and recombinant Ov33 and OvL3-1 proteins. Higher levels of cytokines were produced in response to OvAgs in sowdah and EN/PI than in GEN subjects. Peripheral blood mononuclear cells did not produce interferon-gamma in response to antigens. OvAg induced interleukin (IL)-5, IL-2, granulocyte-macrophage colony-stimulating factor (GM-CSF), and soluble IL-2 receptor. EN/PI and sowdah persons produced significantly more IL-5 and IL-2 than GEN subjects, and EN/PI subjects had significantly higher GM-CSF levels than GEN persons. The low IL-5 and GM-CSF levels in GEN subjects were increased by addition of exogenous IL-2. Ov33 and OvL3-1 stimulated production of IL-10 and less IL-5 and IL-2. The study groups did not show a strict Th2-like cytokine response.

Characterization of enzymatically active Onchocerca volvulus Cu/Zn superoxide dismutase expressed in Escherichia coli

The Onchocerca volvulus superoxide dismutase was expressed in Escherichia coli, using a protocol designed to produce the native enzyme rather than a fusion protein. The recombinant O. volvulus superoxide dismutase (rOVSOD) was found in the cytosol of the disrupted bacteria and represented > 10% of the total bacterial protein. The enzyme was purified to homogeneity using DEAE-Sepharose chromatography, followed by phenyl-Sepharose chromatography. The rOVSOD was enzymatically active which was demonstrated by its reactivity with O2.- produced either by the xanthine-xanthine oxidase system or by stimulated eosinophils. The specific activity was determined to be 4668 U mg-1. This activity could be blocked by rabbit antiserum raised against the rOVSOD. The maximal activity was obtained upon supplementation of the bacterial growth media and enzyme buffer with copper and zinc ions. Activity characteristics in the presence of inhibitors was also characteristic of a Cu/Zn superoxide dismutase. The rOVSOD has an apparent subunit molecular mass of 16,000 in SDS-PAGE. The active enzyme behaves as a dimer of 32 kDa as determined by gel filtration.

HLA-D alleles associated with generalized disease, localized disease, and putative immunity in Onchocerca volvulus infection

Human infections with the tissue nematode Onchocerca volvulus result in a variety of clinical conditions that possibly include protective immunity. In a West African area hyperendemic for human onchocerciasis, 120 residents were classified according to clinical and laboratory findings as presenting with generalized onchocerciasis, localized onchocerciasis, or as being putatively immune. The three groups differed in the distribution of HLA-D variants as determined by DNA typing. The most pronounced differences were found among alleles of the DQ loci. The haplotype DQA1*0501-DQB1*0301 was significantly more frequent among putatively immune individuals than among patients with generalized or localized disease. Conversely, DQA1*0101-DQB1*0501 and, independently, the allele DQB1*0201 were more frequent in generalized disease than in localized disease or putative immunity. In these correlations, the frequencies of allelic variants were in localized disease intermediate to those of the two other groups. The only distinct association found with localized disease was that of the DP allele DPB1*0402. The findings indicate that HLA-D variants influence the course of O. volvulus infection and help to define a state that may reflect protective immunity.

Onchocerca volvulus provides ligands for the stimulation of human gamma/delta T lymphocytes expressing V delta 1 chains

Peripheral blood mononuclear cells (PBMC) from 8 onchocerciasis patients, treated or not with ivermectin, were analyzed for phenotypic cell surface markers. A significant increase (P < .05) in gamma/delta T cells expressing the V delta 1 chain compared with normal and endemic controls was detected in all patients. PBMC populations from onchocerciasis patients were not expanded after restimulation with Onchocerca volvulus antigens in vitro, but both V delta 1 and V delta 2 T cells from normal donors were increased significantly in response to O. volvulus and Mycobacterium tuberculosis (P < .05), respectively. Frozen sections of all 5 onchocerca nodules tested demonstrated an increased number of CD3+ cells in the vicinity of the adult worm, in all cases expressing the alpha/beta T cell receptor and in 2 patients also expressing the gamma/delta T cell receptor; 60% of T cells expressed the activation marker Ki67. These data suggest that O. volvulus provides ligands to V delta 1 T cells.

Epidemiological studies of onchocerciasis in southern Benin

We studied the prevalence of human onchocerciasis in four geographically different regions of the southern part of Benin in West Africa. In a total of thirteen villages 1596 individuals were examined for clinical and parasitological signs of onchocerciasis. Prevalence of microfilariae of Onchocerca volvulus in skin snips was 29% in region I (lower Oueme river), 64% in region II (Mono river), 56% in region III (upper Oueme river) and 70% in region IV (Okpara river). Based on endemicity criteria of the WHO regions II and IV were found to be hyperendemic, region III mesoendemic and region I hypoendemic for onchocerciasis. The community microfilarial load ranged from 4 mf/mg skin in the hypoendemic region to 10.5 mf/mg skin in the hyperendemic regions. The prevalence of nodules was 21% in region I, 30% in region II, 17% in region III and 41% in region IV. The overall prevalence of chronic onchocercal dermatitis was 12%. Of 689 individuals infected with O. volvulus 388 were treated with a single dose of ivermectin.

Characterization of a recombinant T cell and B cell reactive polypeptide of Onchocerca volvulus

To identify potentially protective Ag of the filarial nematode Onchocerca volvulus on the molecular level we screened a cDNA library of O. volvulus with a human serum raised against radiation-attenuated infective larvae of O. volvulus. A cDNA clone of 218 bp (OvL3-1) was selected for further studies. It was expressed in Escherichia coli and affinity purified recombinant polypeptide was tested for its ability to stimulate in vitro PBMC from African onchocerciasis patients and PBMC from chimpanzees experimentally infected with O. volvulus. An enhanced cell proliferation by PBMC was observed in many patients after stimulation with the recombinant OvL3-1 polypeptide. In addition, some patients' PBMC responded to OvL3-1 stimulation with enhanced IL-2 production. Infected chimpanzees also showed an increase in T cell proliferation. Onchocerciasis patients had variable levels of specific antibodies directed to the recombinant polypeptide when sera were tested by ELISA. A mAb directed against the recombinant protein located the native target Ag in the muscles of the adult worm. The molecular mass of native OvL3-1 was found to be 50 kDa on immunoblots. Polymerase chain reaction analysis of RNA from different life stages of the parasite showed that OvL3-1 is transcribed in all parasite stages within the mammalian host. A homologous gene is also present in other filarial parasites. The protein corresponding to OvL3-1, therefore, represents an immunogen present during the whole life-span of the parasite, and because of its B and T cell stimulatory properties, it may be a candidate for a protective Ag in human filariasis.

Characterization of a recombinant T cell and B cell reactive polypeptide of Onchocerca volvulus

To identify potentially protective Ag of the filarial nematode Onchocerca volvulus on the molecular level we screened a cDNA library of O. volvulus with a human serum raised against radiation-attenuated infective larvae of O. volvulus. A cDNA clone of 218 bp (OvL3-1) was selected for further studies. It was expressed in Escherichia coli and affinity purified recombinant polypeptide was tested for its ability to stimulate in vitro PBMC from African onchocerciasis patients and PBMC from chimpanzees experimentally infected with O. volvulus. An enhanced cell proliferation by PBMC was observed in many patients after stimulation with the recombinant OvL3-1 polypeptide. In addition, some patients' PBMC responded to OvL3-1 stimulation with enhanced IL-2 production. Infected chimpanzees also showed an increase in T cell proliferation. Onchocerciasis patients had variable levels of specific antibodies directed to the recombinant polypeptide when sera were tested by ELISA. A mAb directed against the recombinant protein located the native target Ag in the muscles of the adult worm. The molecular mass of native OvL3-1 was found to be 50 kDa on immunoblots. Polymerase chain reaction analysis of RNA from different life stages of the parasite showed that OvL3-1 is transcribed in all parasite stages within the mammalian host. A homologous gene is also present in other filarial parasites. The protein corresponding to OvL3-1, therefore, represents an immunogen present during the whole life-span of the parasite, and because of its B and T cell stimulatory properties, it may be a candidate for a protective Ag in human filariasis.

Functionally distinct human T-lymphocyte clones sharing potent suppressive activity on immunoglobulin secretion

T-lymphocyte clones derived from populations sensitized to alloantigens in vitro were tested for their regulatory effects on pokeweed mitogen-stimulated immunoglobulin (Ig) secretion. Clones with natural killer (NK)-like cytotoxicity and/or suppressive activity for lymphoproliferative (LP) responses potently inhibited Ig secretion. Moreover, certain alloproliferative T4+ interleukin-2 (IL-2)-secreting 'helper' clones shared this strong suppressive activity on Ig secretion. The remaining clones enhanced, rather than suppressed, Ig production. Inhibition by all types of suppressive clones appeared not to be restricted by MHC products, since allogeneic HLA-mismatched donors were suppressed as efficiently as the autologous donor. Suppression was radioresistant, and was apparently not caused by absorption of IL-2, or cytotoxicity of the clones. Suppression was still detectable at plateau levels when cloned cells were added as late as 96 hr after the initiation of the cultures, suggesting an inhibitory mechanism divorced from early B-cell activation events. Thus, T-lymphocyte clones with distinct different functional activities share similar profound suppressive effects on Ig secretion in vitro.

[Serum inhibition factor in acute viral hepatitis]

Sera from patients with acute viral hepatitis were found to inhibit the in vitro proliferation of normal lymphocytes induced by different mitogens and antigens. SIF interfered with the intermediate phase of mitogen induced lymphocyte activation which was defined by protein and RNA synthesis indicating that SIF acts as an antiactivator and may belong to immunoregulatory physiologic serum factors. The active moiety could be separated from immunoglobulins and other proteins by means of gel filtration, anion exchange and affinity chromatography. The major SIF activity always copurified with albumin. Evaluation of SIF in sera from patients with acute and protracted viral hepatitis may be helpful in determining the outcome of hepatitis. Thus, fall of SIF activity during acute viral hepatitis always indicated complete recovery while persistence of SIF correlated with ongoing inflammatory process and persistent viral infection.

[Lung edema after administration of hydrochlorothiazide. A rare and life-threatening side effect]

Recurrent pulmonary oedema occurred in a 62-year-old woman after repeated intake of hydrochlorothiazide-triamterene tablets. Eight similar reports in the medical literature suggested it to be a rare case of intolerance to hydrochlorothiazide. The lymphocyte transformation test proved an allergic genesis: there was significant stimulation of patient lymphocytes by active agent/metabolite serum of hydrochlorothiazide but not triamterene.

Serum inhibitory factors (SIF) in patients with acute and chronic hepatitis and their clinical significance

Serum inhibitory factors (SIF) were demonstrated in a follow-up study in eighteen patients with HBSAg-positive viral hepatitis, in nine patients with chronic persistent hepatitis (CPH) and in six patients with progressive viral hepatitis (CAH). In addition these factors were studied in fifteen patients with HBSAg-positive and HBSAg-negative CAH. SIF appeared during the incubation period up to 4 weeks before onset and disappeared in most instances within 4 weeks after onset of jaundice. Sera from patients with CPH showed no marked inhibitory activity when studied over a period of up to 3 years as compared to patients with a progressive course of hepatitis. The presense of SIF may depend upon persistence of virus, and may help to predict the development of chronic hepatitis.