Evasion of immunity by nematode parasites causing chronic infections

Haematological indices and immune response profiles in dogs naturally infected and co-infected with Dirofilaria repens and Babesia canis

Co-infections with Dirofilaria repens and Babesia canis are rarely reported in the literature and there is very limited knowledge of their impact on canine health. Central Poland is endemic for both parasites, posing a risk of co-infections in dogs. To evaluate the impact of co-infection with B. canis and D. repens on canine health, four groups of dogs were examined: healthy dogs, dogs infected with B. canis, dogs infected with D. repens and dogs co-infected with both species. Blood parameters indicative of anaemia, kidney and liver damage were analysed statistically. Additionally, expression levels of immune response genes were quantified and compared, to define the type of immune response typically encountered in single- and co-infections. In dogs infected with D. repens, no major alterations in blood parameters were observed. Dogs infected with B. canis suffered from anaemia, kidney and liver insufficiency. In contrast, dogs co-infected with D. repens and B. canis showed milder alternation in blood biochemical parameters associated with liver (ALP activity) and kidney (serum urea and creatinine levels) dysfunction, compared to dogs infected only with B. canis. The expression of genes associated with cellular (Th1-mediated) (STAT4 and INF-γ), humoral (Th2-mediated) (STAT6, GATA3, SOCS3, IL-13) and regulatory (IL-10) responses was quantified. For this analysis, dogs infected with B. canis were divided into two groups-'Babesia 1' (mild babesiosis), 'Babesia 2' (severe babesiosis). All the tested factors, except INF-γ, were found to be expressed in dogs infected with D. repens. In 'Babesia 1' dogs, expression of GATA3 was highest, while in 'Babesia 2'-INF-γ and SOCS3 dominated. IL-13 expression was predominant in dogs infected with D. repens, and STAT6 and IL-10 predominated in dogs with co-infections.

Immunity to Soil-Transmitted Helminths: Evidence From the Field and Laboratory Models

Infection with soil-transmitted helminths (STH) remains a major burden on global health and agriculture. Our understanding of the immunological mechanisms that govern whether an individual is resistant or susceptible to infection is derived primarily from model infections in rodents. Typically, experimental infections employ an artificially high, single bolus of parasites that leads to rapid expulsion of the primary infection and robust immunity to subsequent challenges. However, immunity in natura is generated slowly, and is only partially effective, with individuals in endemic areas retaining low-level infections throughout their lives. Therefore, there is a gap between traditional model STH systems and observations in the field. Here, we review the immune response to traditional model STH infections in the laboratory. We compare these data to studies of natural infection in humans and rodents in endemic areas, highlighting crucial differences between experimental and natural infection. We then detail the literature to date on the use of "trickle" infections to experimentally model the kinetics of natural infection.

Identification and preliminary characterization of Hc-clec-160, a novel C-type lectin domain-containing gene of the strongylid nematode Haemonchus contortus

Background

The strongylid parasite Haemonchus contortus causes severe anemia in domestic animals worldwide. Effective preventive and therapeutical agents are lacking, because of drug resistance and that little is known about the molecular mechanism of the interaction between H. contortus and host cells.

Methods

A new gene, Hc-clec-160, was discovered with RT-PCR. Transcriptional levels of Hc-clec-160 and Ce-clec-160 throughout different growth phases of corresponding nematodes were assayed by qPCR. Immunofluorescence staining of paraffin section were performed to determine the protein localization in adult worms of H. contortus. To monitor the promoter capacity of the 5'-flanking region of Ce-clec-160, micro-injection was used. Overexpression and RNAi constructs was carried out in the N2 strain of Caenorhabditis elegans to find out the gene function of Hc-clec-160.

Results

The full-length cDNA of 1224 bp of Hc-clec-160 was cloned by RT-PCR. The corresponding gene contained twelve exons. Its transcripts peaked in male adult worms. Hc-CLEC-160 was predicted to have a Willebrand factor type A (vWA) domain and a C-type lectin domain. The proteins were not detected by expression in C. elegans or paraffin section experiments in adult of H. contortus. Knockdown of Ce-clec-160 expression in C. elegans by RNAi resulted in shortened body length and decreased brood size.

Conclusions

In this experiment, a new gene Hc-clec-160 was obtained in H. contortus and its function was addressed using a model organism: C. elegans. Our study showed that Hc-clec-160 possesses characteristics similar to those of Ce-clec-160 and plays an important role in the growth and reproduction of this parasitic nematode.

Electronic supplementary material

The online version of this article (10.1186/s13071-018-3005-3) contains supplementary material, which is available to authorized users.

Heligmosomoides polygyrus Venom Allergen-like Protein-4 (HpVAL-4) is a sterol binding protein

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Heligmosomoides polygyrus Venom Allergen-like Protein-4 (HpVAL-4) was produced in plants as a glycosylated protein.

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The crystal structure of HpVAL-4 was solved and reveals three distinct cavities.

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These cavities are the central cavity; the sterol-binding caveolin-binding motif (CBM); and the palmitate-binding cavity.

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The central cavity of Hp-VAL-4 lacks the characteristic histidines that coordinate divalent cations.

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Hp-VAL-4 binds sterol in vivo and in vitro.

Heligmosomoides polygyrus bakeri is a model parasitic hookworm used to study animal and human helminth diseases. During infection, the parasite releases excretory/secretory products that modulate the immune system of the host. The most abundant protein family in excretory/secretory products comprises the venom allergen-like proteins (VALs), which are members of the SCP/TAPS (sperm-coating protein/Tpx/antigen 5/pathogenesis related-1/Sc7) superfamily. There are >30 secreted Heligmosomoides polygyrus VAL proteins (HpVALs) and these proteins are characterised by having either one or two 15 kDa CAP (cysteine-rich secretory protein (CRISP)/antigen 5/pathogenesis related-1) domains. The first known HpVAL structure, HpVAL-4, refined to 1.9 Å is reported. HpVAL-4 was produced as a homogeneously glycosylated protein in leaves of Nicotiana benthamiana infiltrated with recombinant plasmids, making this plant expression platform amenable for the production of biological products. The overall topology of HpVAL-4 is a three layered αβα sandwich between a short N-terminal loop and a C-terminal cysteine rich extension. The C-terminal cysteine rich extension has two strands stabilized by two disulfide bonds and superposes well with the previously reported extension from the human hookworm Necator americanus Ancylostoma secreted protein-2 (Na-ASP-2). The N-terminal loop is connected to alpha helix 2 via a disulfide bond previously observed in Na-ASP-2. HpVAL-4 has a central cavity that is more similar to the N-terminal CAP domain of the two CAP Na-ASP-1 from Necator americanus. Unlike Na-ASP-2, mammalian CRISP, and the C-terminal CAP domain of Na-ASP-1, the large central cavity of HpVAL-4 lacks the two histidines required to coordinate divalent cations. HpVAL-4 has both palmitate-binding and sterol-binding cavities and is able to complement the in vivo sterol export phenotype of yeast mutants lacking their endogenous CAP proteins. More studies are required to determine endogenous binding partners of HpVAL-4 and unravel the possible impact of sterol binding on immune-modulatory functions.

Of dogs and hookworms: man's best friend and his parasites as a model for translational biomedical research

We present evidence that the dog hookworm (Ancylostoma caninum) is underutilised in the study of host-parasite interactions, particularly as a proxy for the human-hookworm relationship. The inability to passage hookworms through all life stages in vitro means that adult stage hookworms have to be harvested from the gut of their definitive hosts for ex vivo research. This makes study of the human-hookworm interface difficult for technical and ethical reasons. The historical association of humans, dogs and hookworms presents a unique triad of positive evolutionary pressure to drive the A. caninum-canine interaction to reflect that of the human-hookworm relationship. Here we discuss A. caninum as a proxy for human hookworm infection and situate this hookworm model within the current research agenda, including the various 'omics' applications and the search for next generation biologics to treat a plethora of human diseases. Historically, the dog hookworm has been well described on a physiological and biochemical level, with an increasing understanding of its role as a human zoonosis. With its similarity to human hookworm, the recent publications of hookworm genomes and other omics databases, as well as the ready availability of these parasites for ex vivo culture, the dog hookworm presents itself as a valuable tool for discovery and translational research.

Understanding the role of antibodies in murine infections with Heligmosomoides (polygyrus) bakeri: 35 years ago, now and 35 years ahead

The rodent intestinal nematode H.p.bakeri has played an important role in the exploration of the host-parasite relationship of chronic nematode infections for over six decades, since the parasite was first isolated in the 1950s by Ehrenford. It soon became a popular laboratory model providing a tractable experimental system that is easy to maintain in the laboratory and far more cost-effective than other laboratory nematode-rodent model systems. Immunity to this parasite is complex, dependent on antibodies, but confounded by the parasite's potent immunosuppressive secretions that facilitate chronic survival in murine hosts. In this review, we remind readers of the state of knowledge in the 1970s, when the first volume of Parasite Immunology was published, focusing on the role of antibodies in protective immunity. We show how our understanding of the host-parasite relationship then developed over the following 35 years to date, we propose testable hypotheses for future researchers to tackle, and we speculate on how the new technologies will be applied to enable an increasingly refined understanding of the role of antibodies in host-protective immunity, and its evasion, to be achieved in the longer term.

Dietary and prophylactic iron supplements : Helpful or harmful?

Mild hypoferremia represents an aspect of the ability of the body to withhold iron from pathogenic bacteria, fungi, and protozoa, and from neoplastic cells. However, our iron-withholding defense system can be thwarted by practices that enhance iron overload such as indiscriminate iron fortification of foods, medically prescribed iron supplements, alcohol ingestion, and cigarette smoking. Elevated standards for normal levels of iron can be misleading and even dangerous for individuals faced with medical insults such as chronic infection, neoplasia, cardiomyopathy, and arthritis. We are becoming increasingly aware that the wide-spread hypoferremia in human populations is a physiological response to insult rather than a pathological cause of insult, and that attempts to correct the condition by simply raising iron levels may not only be misguided but may actually impair host defense.

Helminth communities from two urban rat populations in Kuala Lumpur, Malaysia

BACKGROUND

The prevalence of parasitic infections among commensal animals such as black and brown rats in many tropical countries is high and in comparison with studies on rodents in temperate climates, little is known about the community structure of their parasites. Rodent borne parasites pose threats to human health since people living in close proximity to rodent populations can be exposed to infection.

METHODS

The helminth community structures of two urban rat populations in Kuala Lumpur, Malaysia were investigated. The rats were from two contrasting sites in the city caught over a period of 21 months in 2000-2002.

RESULTS

Eleven species of helminth parasites comprising seven nematodes (Heterakis spumosum, Mastophorus muris, Nippostrongylus brasiliensis, Syphacia muris, Pterygodermatites tani/whartoni, Gongylonema neoplasticum, Angiostrongylus malaysiensis), three cestodes (Hymenolepis (Rodentolepis) nana, H. diminuta and Taenia taeniaeformis) and one acanthocephalan (Moniliformis moniliformis) were recovered from 346 Rattus rattus and 104 R. norvegicus from two urban sites, Bangsar and Chow Kit, during 2000-2002. Rattus rattus harboured over 60% of all helminths compared with R. norvegicus, although both host species played a dominant role in the different sites with, for example R. norvegicus at Bangsar and R. rattus at Chow Kit accounting for most of the nematodes. Overall 80% of rats carried at least one species of helminth, with the highest prevalences being shown by H. diminuta (35%), H. spumosum (29.8%) and H. nana (28.4%). Nevertheless, there were marked differences in prevalence rates between sites and hosts. The influence of extrinsic (year, season and site) and intrinsic (species, sex and age) factors affecting infracommunity structure (abundance and prevalence of infection) and measures of component community structure were analyzed.

CONCLUSIONS

Since at least two species of rat borne helminths in Kuala Lumpur have the potential to infect humans, and these showed high prevalences in the rats, the assessment and regular monitoring of infections carried by wild rodents have important roles to play in public health.

B-cells get the T-cells but antibodies get the worms

Two recent papers published in Immunity and Cell Host & Microbe underline the great importance of B cells and of antibodies (Abs) in orchestrating crucial T helper cell type 2 (Th2) protective immune responses to gastrointestinal nematodes. The findings in animal models now raise major questions as to how B cells and Abs carry out these functions in humans. Here we discuss recent technological advances in humanizing animal models at the level of both Abs and their Fc-receptors, that might provide some answers.

C-type lectins from the nematode parasites Heligmosomoides polygyrus and Nippostrongylus brasiliensis

The C-type lectin superfamily is highly represented in all metazoan phyla so far studied. Many members of this superfamily are important in innate immune defences against infection, while others serve key developmental and structural roles. Within the superfamily, many proteins contain multiple canonical carbohydrate-recognition domains (CRDs), together with additional non-lectin domains. In this report, we have studied two gastrointestinal nematode parasites which are widely used in experimental rodent systems, Heligmosomoides polygyrus and Nippostrongylus brasiliensis. From cDNA libraries, we have isolated 3 new C-type lectins from these species; all are single-CRD proteins with short additional N-terminal domains. The predicted Hp-CTL-1 protein contains 156 aa, Nb-CTL-1 191 aa and Nb-CTL-2 183 aa; all encode predicted signal peptides, as well as key conserved sequence motifs characteristic of the CTL superfamily. These lectins are most similar to C. elegans CLEC-48, 49 and 50, as well as to the lectin domains of mammalian immune system proteins CD23 and CD206. RT-PCR showed that these H. polygyrus and N. brasiliensis genes are primarily expressed in the gut-dwelling adult stages, although Nb-CTL-2 transcripts are also prominent in the free-living infective larval (L3) stage. Polyclonal antibodies raised to Hp-CTL-1 and Nb-CTL-1 reacted to both proteins by ELISA, and in Western blot analysis recognised a 15-kDa band in secreted proteins of adult N. brasiliensis (NES) and a 19-kDa band in H. polygyrus ES (HES). Anti-CTL-1 antibody also bound strongly to the cuticle of adult H. polygyrus. Hence, live parasites release C-type lectins homologous to some key receptors of the mammalian host immune system, raising the possibility that these products interfere in some manner with immunological recognition or effector function.

Helminth species richness in wild wood mice, Apodemus sylvaticus, is enhanced by the presence of the intestinal nematode Heligmosomoides polygyrus

We analysed 3 independently collected datasets of fully censused helminth burdens in wood mice, Apodemus sylvaticus, testing the a priori hypothesis of Behnke et al. (2005) that the presence of the intestinal nematode Heligmosomoides polygyrus predisposes wood mice to carrying other species of helminths. In Portugal, mice carrying H. polygyrus showed a higher prevalence of other helminths but the magnitude of the effect was seasonal. In Egham, mice with H. polygyrus showed a higher prevalence of other helminth species, not confounded by other factors. In Malham Tarn, mice carrying H. polygyrus were more likely to be infected with other species, but only among older mice. Allowing for other factors, heavy residual H. polygyrus infections carried more species of other helminths in both the Portugal and Egham data; species richness in Malham was too low to conduct a similar analysis, but as H. polygyrus worm burdens increased, so the prevalence of other helminths also increased. Our results support those of Behnke et al. (2005), providing firm evidence that at the level of species richness a highly predictable element of co-infections in wood mice has now been defined: infection with H. polygyrus has detectable consequences for the susceptibility of wood mice to other intestinal helminth species.

Heligmosomoides bakeri: a model for exploring the biology and genetics of resistance to chronic gastrointestinal nematode infections

The intestinal nematode Heligmosomoides bakeri has undergone 2 name changes during the last 4 decades. Originally, the name conferred on the organism in the early 20th century was Nematospiroides dubius, but this was dropped in favour of Heligmosomoides polygyrus, and then more recently H. bakeri, to distinguish it from a closely related parasite commonly found in wood mice in Europe. H. bakeri typically causes long-lasting infections in mice and in this respect it has been an invaluable laboratory model of chronic intestinal nematode infections. Resistance to H. bakeri is a dominant trait and is controlled by genes both within and outside the MHC. More recently, a significant QTL has been identified on chromosome 1, although the identity of the underlying genes is not yet known. Other QTL for resistance traits and for the accompanying immune responses were also defined, indicating that resistance to H. bakeri is a highly polygenic phenomenon. Hence marker-assisted breeding programmes aiming to improve resistance to GI nematodes in breeds of domestic livestock will need to be highly selective, focussing on genes that confer the greatest proportion of overall genetic resistance, whilst leaving livestock well-equipped genetically to cope with other types of pathogens and preserving important production traits.

Expansion and activation of CD4(+)CD25(+) regulatory T cells in Heligmosomoides polygyrus infection

Regulatory T cell responses to infectious organisms influence not only immunity and immunopathology, but also responses to bystander antigens. Mice infected with the gastrointestinal nematode parasite Heligmosomoides polygyrus show an early Th2-dominated immune response (days 7-14), but by day 28 a strongly regulatory profile is evident with antigen-specific IL-10 release and elevated frequency of CD4(+) T cells bearing surface TGF-beta. CD4(+)CD25(+) T cells from infected mice show enhanced capacity to block in vitro effector T cell proliferation. CD4(+)CD25(+) cell numbers expand dramatically during infection, with parallel growth of both CD25(+)Foxp3(+) and CD25(+)Foxp3(-) subsets. CTLA-4 and glucocorticoid-induced tolerance-associated receptor, also associated with regulatory T cell function, become more prominent, due to both expanded CD25(+) cell numbers and increased expression among the CD25(-) population. Both intensity and frequency of CD103 expression by CD4(+) T cells rise significantly, with greatest expansion among CD25(+)Foxp3(+) cells. While TGF-beta expression is observed among both CD25(+)Foxp3(+) and CD25(+)Foxp3(-) subsets, it is the latter population which shows higher TGF-beta staining following infection. These data demonstrate in a chronic helminth infection that Foxp3(+) regulatory T cells are stimulated, increasing CD103 expression in particular, but that significant changes occur to other populations including expansion of CD25(+)TGF-beta(+)Foxp3(-) cells, and induction of CTLA-4 on CD25(-) non-regulatory lymphocytes.

Gastrointestinal helminths in indigenous and exotic chickens in Vietnam: association of the intensity of infection with the Major Histocompatibility Complex

This study compared the prevalence and intensity of infections of helminths in 2 chicken breeds in Vietnam, the indigenous Ri and the exotic Luong Phuong. Also, possible correlations with the Major Histocompatibility Complex (MHC) were tested. The most prevalent helminths were Ascaridia galli, Heterakis beramporia, Tetrameres mothedai, Capillaria obsignata, Raillietina echinobothrida and Raillietina tetragona. Differences in prevalence and intensity of infection were found between the 2 breeds. Comparing the 2 groups of adult birds, Ri chickens were observed to have higher prevalence and infection intensities of several species of helminths, as well as a higher mean number of helminth species. In contrast, A. galli and C. obsignata were shown to be more prevalent in Luong Phuong chickens. Furthermore, an age-dependent difference was indicated in the group of Ri chickens in which the prevalence and the intensity of infection was higher for the adult than the young chickens for most helminths. The most notable exception was the significantly lower prevalence and intensities of A. galli in the group of adult chickens. In contrast, the prevalence and intensity were very similar in both age groups of Luong Phuong chickens. Using a genetic marker located in the MHC, a statistically significant correlation between several MHC haplotypes and the infection intensity of different helminth species was inferred. This is the first report of an association of MHC haplotype with the intensity of parasite infections in chickens.

Screening for immunomodulatory proteins of the intestinal parasitic nematode Heligmosomoides polygyrus

Parasitic nematodes are constantly exposed to the immune effector mechanisms of their hosts. One strategy of the worms to cope with these defence reactions is the secretion of modulatory proteins that down-regulate cell-mediated immune responses. We analysed the proliferation of mesenteric lymph node cells of mice infected with Heligmosomoides polygyrus and showed that cellular proliferation was strongly suppressed in the chronic phase of infection. To identify proteins of H. polygyrus that are involved in parasite-induced immunomodulation, worm extract and culture supernatant of adult H. polygyrus were fractionated by gel chromatography and activity of each fraction was determined. One of the fractions (fraction 9) of worm extract as well as worm secretory products inhibited the antigen-specific cellular proliferation by about 40%. This reduced cellular reactivity coincided with a down-regulation of inducible nitric oxide production of mouse macrophages by 57%. Furthermore, fraction 9 contained antigens that were recognized by IgE antibodies of H. polygyrus-infected mice and induced degranulation of an IgE-sensitized basophil cell line. Single proteins of fraction 9 were analysed by mass spectrometry. These data suggest that antigens that are recognised by IgE antibodies might play an important role in immunomodulation exerted by nematode infections.

The role of TGF-β in mice infected with Heligmosomoides polygyrus

Hyporesponsiveness induced by Heligmosomoides polygyrus was quantified and the relationship between TGF-beta and inflammation was identified in BALB/c mice. The immune response and pathological changes modified by neutralization of TGF-beta were characterized in vivo. Nine and twelve days following infection, BALB/c mice were injected intraperitoneally with anti-TGF-beta (1,2,3) antibodies, isotype control antibodies or isosmotic solution. We assessed both Th1 and Th2 related cytokines production ex vivo and in vitro, IgA, the number of CD4+ cells, and eosinophils in the lamina propria and the villus : crypt ratio in the small intestine 6 weeks after infection. The pattern of cytokine production differed in the intestine, peritoneal fluid and serum. In mice infected with H. polygyrus the concentrations of IL-5, IL-12, TNF-alpha and IL-10 were raised in the intestine, but in serum the level of cytokines was diminished below the value observed in uninfected mice. The neutralization of TGF-beta converted the pattern of immune response induced by H. polygyrus. The elevation of cytokines in serum coincided with the reduction of cytokine concentration in the intestine or peritoneum. Neutralization of TGF-beta restored infiltration of eosinophils into the lamina propria of the intestine despite the low level of IL-5. We conclude that H. polygyrus infection suppresses the immune response through pathways involving TGF-beta production or activity and that the Th2 related immune response was not affected by neutralization.

Molecular evidence that Heligmosomoides polygyrus from laboratory mice and wood mice are separate species

The gastro-intestinal (GI) nematode Heligmosomoides polygyrus is an important experimental model in laboratory mice and a well-studied parasite of wood mice in the field. Despite an extensive literature, the taxonomy of this parasite in different hosts is confused, and it is unclear whether laboratory and field systems represent the same or different Operational Taxonomic Units (OTUs). Molecular analyses reveal high sequence divergence between H. p. bakeri (laboratory) and H. p. polygyrus (field); 3% difference in the ribosomal DNA Internal Transcribed Spacers (ITS) and 8.6% variation in the more rapidly evolving mitochondrial cytochrome c oxidase I (COI) gene. The COI sequence of U.K. H. p. polygyrus is more similar to H. glareoli from voles than to H. p. bakeri, while a single isolate of H. p. polygyrus from Guernsey confirms the extent of genetic variation between H. p. polygyrus populations. Analysis of molecular variance demonstrated that mtCOI sequence variation is associated primarily with groups with distinct ITS2 sequences, and with host identity, but is not partitioned significantly with a single combined taxon H. polygyrus incorporating European and North American isolates. We conclude therefore that the laboratory OTU should be raised to the level of a distinct species, as H. bakeri from the laboratory mouse Mus musculus, and we reject the hypothesis that H. bakeri has diverged from H. polygyrus in the recent past following introduction into America. However, we are unable to reject the hypothesis that H. polygyrus and H. bakeri are sister taxa, and it may be that H. polygyrus is polyphyletic or paraphyletic.

Immune-mediated regulation of chronic intestinal nematode infection

Gastrointestinal nematode infection is extremely prevalent worldwide in humans and animals. Infection levels vary between individuals in infected populations and exhibit a negative binomial distribution, and some individuals appear to be predisposed to certain infection levels. Moreover, infection tends to be chronic, despite evidence for the acquisition of some degree of acquired immunity. The host is subject to constant and repeated antigenic challenge, and individuals vary in the response they make. While a considerable amount of information is emerging on the immunoregulatory mechanisms operating during acute nematode infection from a variety of laboratory model systems, relatively little work has been carried out on the immune mechanisms underlying chronic infection. This review details some of the work that has addressed this important facet of gut nematode infection, highlighting studies from model systems that give insight into the induction of nonprotective immunity, while at the same time avoiding the induction of host-damaging pathology.

Medium-term temporal stability of the helminth component community structure in bank voles (Clethrionomys glareolus) from the Mazury Lake District region of Poland

The structure of helminth communities in wild rodents is subject to seasonal variation, and is dependent on host age within years. Although between-year variation has been monitored, seldom has it been assessed rigorously by appropriate multifactorial analysis with potentially confounding factors taken into account. In this study we tested the null hypothesis that despite seasonal, host age and sex effects, helminth communities should show relative stability between years. Over a period of 3 years (1998–2000) we sampled bank vole (Clethrionomys glareolus) populations (totaln=250) at 2 points in the year: in spring, at the start of the breeding season, and in autumn, after the cessation of breeding. In spite of seasonal differences and strong age effects, the between-year effects were surprisingly small. Measures of component community structure (Berger-Parker dominance index, the dominant species,S. petrusewiczi) did not vary, or varied only slightly from year to year. The majority of measures of infracommunity structure [Brillouin's index of diversity, prevalence of all helminths combined, prevalence and abundance ofH. mixtum(the most prevalent helminth), mean species richness] did not differ significantly between years when other factors such as age, sex and seasonal variation had been taken into account. Some between-year variations were found (at the component community level, Simpson's index of diversity; at the infracommunity level, prevalence and abundance ofS. petrusewicziand abundance of all helminths combined), but even these were modest in comparison to seasonal and age differences, and were primarily attributable toS. petrusewiczi. We conclude that despite dynamic within-year fluctuations, helminth communities in bank voles in this region of Poland show relative stability across years. The sporadic occurrence of individual platyhelminths at low prevalence, makes little difference to the overall structure, which is largely maintained by the key roles played by the dominant intestinal nematodes of bank voles and the rarer species collectively.

Cellular and serological responses in resistant and susceptible mice exposed to repeated infection with Heligmosomoides polygyrus bakeri

An experiment was carried out to compare the parasitological and immunological responses of SWR and CBA mice to trickle (repeated) infection with Heligmosomoides polygyrus. Male mice were given 125 L3 once per week and were killed in groups, together with naïve control mice, weekly until week 8. Worm burdens accumulated in CBA, stabilizing in week 5 in excess of 400 worms and remaining high until week 8. In contrast in SWR worm burdens peaked in week 3 at a mean worm burden of 129 and then fell sharply so that by week 6, despite continuing re-infection, no more worms were recovered from these mice. SWR mice showed a marked mast cell and mMCP-1 response, peaking in weeks 2-3, whereas in CBA mice these responses were slower, and even at their height in week 8 still less intense than those in SWR mice. Both strains responded initially with a very similar goblet cell response, which declined in SWR mice as worms were eliminated, but was sustained in CBA mice until week 8. Serum TNFalpha concentrations were higher in SWR mice throughout the experiment. Infection elicited strong serological responses against adult and L4 antigens in both SWR and CBA mice, involving all the isotypes tested (IgG1, IgA and IgE). Anti-L3 responses were examined only for IgG1. However, only two responses differed significantly between the strains: the IgE response to L4 antigens was more intense in SWR mice, and interestingly and unexpectedly, the IgG1 response to adult worm antigens was more intense in CBA mice. These results reflect the activation of predominantly Th2-driven effector mechanisms, that may be associated with host-protective immunity developing under the trickle infection protocol exploited in these experiments.

The relative involvement of Th1 and Th2 associated immune responses in the expulsion of a primary infection of Heligmosomoides polygyrus in mice of differing response phenotype

T helper cell (Th1 and Th2) associated responses were examined following a primary infection with the gastrointestinal nematode Heligmosomoides polygyrus in five inbred strains of mice with different resistance phenotypes. Levels of (i) mast cell protease, (ii) specific IgE, (iii) nitric oxide and (iv) specific IgG2a, as markers of Th2 and Th1 associated responses, respectively, were determined in sera and intestinal fluids and correlated with worm burdens. The "fast" responder (resistant) strains SWR and SJL produced strong Th2 and Th1 associated responses respectively in a mutually exclusive fashion. The F1 hybrid (SWRxSJL) F1, showed rapid expulsion of the parasite and expressed both intense Th1 and Th2 responses, suggesting synergism between Th1 and Th2 activity in these mice. The results indicate that both Th2 and Th1 responses operate in mice following a primary infection with H. polygyrus and that each Th response may be involved to a greater or lesser degree within certain strains. Resistance to H. polygyrus was found to correlate only to the intensity of either the gut-associated mastocytosis or nitric oxide production in these strains but not to either specific IgE or IgG2a titres. Chronic infections in the "slow" response phenotype mouse strains CBA and C57BL/10, were associated with both poor Th2 and poor Th1-associated responses attributed to a general parasite-mediated immunosuppression of the host immune response to infection.

Chasing the genes that control resistance to gastrointestinal nematodes

The host-protective immune response to infection with gastrointestinal (GI) nematodes involves a range of interacting processes that begin with recognition of the parasite's antigens and culminate in an inflammatory reaction in the intestinal mucosa. Precisely which immune effectors are responsible for the loss of specific worms is still not known although many candidate effectors have been proposed. However, it is now clear that many different genes regulate the response and that differences between hosts (fast or strong versus slow or weak responses) can be explained by allelic variation in crucial genes associated with the gene cascade that accompanies the immune response and/or genes encoding constitutively expressed receptor/signalling molecules. Major histocompatibility complex (MHC) genes have been recognized for some time as decisive in controlling immunity, and evidence that non-MHC genes are equally, if not more important in this respect has also been available for two decades. Nevertheless, whilst the former have been mapped in mice, only two candidate loci have been proposed for non-MHC genes and relatively little is known about their roles. Now, with the availability of microsatellite markers, it is possible to exploit linkage mapping techniques to identify quantitative trait loci (QTL) responsible for resistance to GI nematodes. Four QTL for resistance to Heligmosomoides polygyrus, and additional QTL affecting faecal egg production by the worms and the accompanying immune responses, have been identified. Fine mapping and eventually the identification of the genes (and their alleles) underlying QTL for resistance/susceptibility will permit informed searches for homologues in domestic animals, and human beings, through comparative genomic maps. This information in turn will facilitate targeted breeding to improve resistance in domestic animals and, in human beings, focused application of treatment and control strategies for GI nematodes.

Interactions involving intestinal nematodes of rodents: experimental and field studies

Multiple species infections with parasitic helminths, including nematodes, are common in wild rodent populations. In this paper we first define different types of associations and review experimental evidence for different categories of interactions. We conclude that whilst laboratory experiments have demonstrated unequivocally that both synergistic and antagonistic interactions involving nematodes exist, field work utilizing wild rodents has generally led to the conclusion that interactions between nematode species play no, or at most a minor, role in shaping helminth component communities. Nevertheless, we emphasize that analysis of interactions between parasites in laboratory systems has been fruitful, has made a fundamental contribution to our understanding of the mechanisms underlying host-protective intestinal immune responses, and has provided a rationale for studies on polyparasitism in human beings and domestic animals. Finally, we consider the practical implications for transmission of zoonotic diseases to human communities and to their domestic animals, and we identify the questions that merit research priority.

Concomitant infections, parasites and immune responses

Concomitant infections are common in nature and often involve parasites. A number of examples of the interactions between protozoa and viruses, protozoa and bacteria, protozoa and other protozoa, protozoa and helminths, helminths and viruses, helminths and bacteria, and helminths and other helminths are described. In mixed infections the burden of one or both the infectious agents may be increased, one or both may be suppressed or one may be increased and the other suppressed. It is now possible to explain many of these interactions in terms of the effects parasites have on the immune system, particularly parasite-induced immunodepression, and the effects of cytokines controlling polarization to the Th1 or Th2 arms of the immune response. In addition, parasites may be affected, directly or indirectly, by cytokines and other immune effector molecules and parasites may themselves produce factors that affect the cells of the immune system. Parasites are, therefore, affected when they themselves, or other organisms, interact with the immune response and, in particular, the cytokine network. The importance of such interactions is discussed in relation to clinical disease and the development and use of vaccines.

The immunobiology of gastrointestinal nematode infections in ruminants

The major gastrointestinal nematode parasites of ruminants all belong to the Order Strongylida and the family Trichostrongyloidea. Despite this close evolutionary relationship, distinct differences exist in the microenvironmental niches occupied by the developmental stages of the various parasites, which may account for the variable susceptibility of the different parasite species to the immune effector mechanisms generated by the host. In addition, different manifestations of resistance have been observed against the adult and larval stages of the same parasite species, and even against the same parasite stage. In particular, both rapid and delayed rejection of infective larval stages of gastrointestinal nematode parasites has been documented. This review will give an overview of the various manifestations of resistance to gastrointestinal nematode parasites of ruminants, as well as the immune mechanisms and antigens associated with the generation of immunity by the ruminant hosts to these parasites. In addition, a working model is provided aimed at reconciling most of the present knowledge on the different immune responses generated during infection with the various parasite rejection profiles. Extrapolation of these results to field conditions will need to take into account the variability imposed by seasonal changes and management practices, as well as the individual variability in immune responsiveness present in outbred animal populations.

Primary infections with Babesia microti are not prolonged by concurrent Heligmosomoides polygyrus

Seven experiments were carried out to test the hypothesis that concurrent infection with the chronic and immunomodulatory intestinal nematode parasites, Heligmosomoides polygyrus, and the piroplasm, Babesia microti, would result in more intense and long-lasting infections with the hemoprotozoan. However, despite variations in the experimental protocols (different mouse strains, varying levels of infection and different intervals between infection with the two species) a significantly higher B. microti parasitaemia was detected on only one occasion, and a significantly lower parasitaemia on two occasions, relative to control mice. In none of our experiments was the duration of infection prolonged. We conclude that the presence of H. polygyrus does not interfere markedly with the host's ability to mount a protective response against B. microti and hence season-dependent peaks of abundance of H. polygyrus in wild rodents are unlikely to present a particular threat to human communities by providing a greater reservoir of infection with B. microti in wild rodents than at other times of the year.

The relationship between circulating and intestinal Heligmosomoides polygyrus-specific IgG1 and IgA and resistance to primary infection

Specific serum and intestinal immunoglobulin (Ig)G1 and IgA responses to Heligmosomoides polygyrus were measured in a panel of seven inbred mouse strains which exhibit 'rapid' (<6 weeks (SWRxSJL)F1), 'fast' (<8 weeks, SJL and SWR), 'intermediate' (10-20 weeks, NIH and BALB/c) or 'slow' (>25 weeks, C57BL/10 and CBA) resolution of primary infections. Mice with 'rapid', 'fast' or 'intermediate' response phenotypes produced greater serum and intestinal antibody responses than those with 'slow' phenotypes. The F1 hybrids ((SWRxSJL)F1) of two 'fast' responder strains showed the earliest antibody response with maximum titres evident within 6 weeks of infection. There was a negative correlation between the serum IgG1 responses and worm burdens in individual mice within a number of mouse strains, and also between serum IgG1 and IgA responses and worm burdens in the 'rapid' ((SWRxSJL)F1) responder strain. The presence of IgG1 in the gut was found to be due to local secretion rather than plasma leakage. Using Western immunoblotting, serum IgG1 from 'rapid' and 'fast' responder but not 'slow' responder mice was found to react with low molecular weight antigens (16-18 kDa) in adult worm excretory/secretory products.

The role of parasite-induced immunodepression, rank and social environment in the modulation of behaviour and hormone concentration in male laboratory mice (Mus musculus)

Peripheral immune responsiveness in male laboratory mice was reduced by infection with the trichostrongyloid nematode Heligmosomoides polygyrus. Responsiveness was also lower among high-ranking (aggressive) males regardless of infection status. Reduced responsiveness in both infected animals and high rankers was associated with elevated serum corticosterone concentration (a potential immunodepressant) and was compounded among high-ranking males by subsequent high aggressiveness. As in previous experiments, only low rankers modulated testosterone secretion in relation to current immunocompetence and corticosterone concentration. The lack of any downregulation of aggression in response to parasite-induced immunodepression contrasted with previous results using antithymocyte serum and may be due to the more localized nature of immunodepression during H. polygyrus infection. However, the additional increase in corticosterone concentration resulting from exposure to female odour and destabilized aggressive social relationships did result in downregulation of aggression among high rankers and of testosterone among mice generally, suggesting that modulation rules of thumb are at least partly dependent on the proximate cues associated with immunodepression.

Immunological interactions between Trichinella spiralis and Heligmosomoides polygyrus: cross reactivity between muscle larvae and antibodies raised to unrelated antigens

It is documented that concurrent infections in mice with the 2 unrelated nematode parasites, Heligmosomoides polygyrus and Trichinella spiralis, can result in delayed rejection of the latter species. The basis of this immunological interference is not completely understood, but a possibility exists that antibodies induced by 1 species may interact with antigens produced by the other parasite. Therefore, it was investigated whether H. polygyrus infections may induce the production of antibodies which could cross react with T. spiralis muscle larval (m.l.) antigens. The results shown here indicate that this assumption is correct, and there is cross reactivity between antibodies produced against H. polygyrus, and T. spiralis m.l. antigens. Furthermore, antibodies which were not specific for either species were also able to bind to T. spiralis m.l. This is in agreement with recent evidence which has shown that antibodies that are not specific for H. polygyrus may still be absorbed by an H. polygyrus homogenate. It is considered that the binding of these antibodies may be involved in manipulation of the host immune response by T. spiralis.

Genetic control of immunity to Heligmosomoides polygyrus: presentation of promiscuous antigens to parasite-specific T cell hybridomas

The role of MHC class II in the presentation of Heligmosomoides polygyrus antigens has been investigated, using a number of T cell hybridomas produced in A and E positive and negative mice. By using fixed and irradiated antigen presenting cells (APC), further evidence has emerged, to support earlier data, that there can be differential processing requirements during the presentation of H. polygyrus antigens by A and E molecules. In concordance with these earlier observations, this work provides further evidence than individual T cells can respond to antigen when presented by more than one MHC molecule. Previously, this evidence has been restricted to individual MHC molecules of the same haplotype, but these data show that H. polygyrus produces antigens which can be presented by both syngeneic and allogeneic MHC molecules. These antigens do not appear to be synonymous with the previously described H. polygyrus superantigen, as presentation is restricted to specific MHC haplotypes. It is proposed that H. polygyrus may produce these antigenic molecules as part of its strategy to manipulate the host immune system.

Prospects for the immunological control of ruminant gastrointestinal nematodes: natural immunity, can it be harnessed?

Current understanding of the mucosal immune response to nematode parasites is briefly reviewed with emphasis on the role of the cytokines interleukins-4 and -12 and gamma interferon (IFN gamma) in the development of T-helper responses in rodents. Data from laboratory animals and ruminants indicate that the events associated with a T-helper 2 (Th2) cell response, notably IgE synthesis, eosinophilia and mucosal mastocytosis are protective. Evidence that effector mechanisms may vary for different parasite species is considered. Current gaps in understanding such as the location in the gut and mechanism of antigen processing and presentation as well as the relative contribution of non-immunological effector responses, such as gut motility and mucus secretion, to worm expulsion are discussed.

Genetic control of acquired resistance to Heligmosomoides polygyrus: overcoming genetically determined weak responder status by strategic immunization with ivermectin-abbreviated infections

The induction of acquired resistance to H. polygyrus, following treatment of mice by a 6 day immunizing infection abbreviated with the anthelmintic drug ivermectin (6d I-AI), was investigated. Four worms were sufficient to elicit > 80% protection against challenge and immunizing infections > 50 worms generated > 95% protection in female NIH mice. A few worms were recovered during the second week from immunized challenged mice but these were rapidly expelled from the gut lumen. Treatment with hydrocortisone from day 10 postinfection, permitted worm burdens to accumulate over the following 2 weeks. The 6d I-AI protocol enabled females of strains previously designated as weak responders to develop potent acquired resistance to challenge (CBA mice showed > 90% protection), although weak responder strain male mice were not significantly protected. Delaying treatment with ivermectin by as little as 24 h resulted in poorer expression of acquired resistance. A positive correlation between the increasing interval from infection to treatment with ivermectin and worm burdens after challenge, and the negative correlation with IgGI antibody responses after challenge indicated that the immunodepressive activities of 7 day and older worms down-regulated local intestinal immune responses. Mice characterized by weak responder phenotype were significantly more sensitive to downregulation than mouse strains showing strong responder phenotype. In consequence, optimal timing of treatment with anthelmintics during exposure to the immunizing infection, intending to minimize exposure to the immunodepressive stages of the parasite, is sufficient to overcome reported genetic constraints on the development of resistance in this system.

Irradiated larval vaccination and antibody responses evaluated in relation to the expression of immunity to Heligmosomoides polygyrus

Infections induced in NIH mice by irradiated (300 Gy) larvae of Heligmosomoides polygyrus effectively stimulated immunity to challenge, whereas unirradiated larvae did not. Importantly, this difference was lost by the elimination of the adult worms arising from unirradiated sensitising infections by drug treatment prior to challenge. No difference in the level of parasite-specific serum and mucosal IgG, IgG1, IgG2a, or IgA was detected between immune mice sensitised either with drug-abbreviated unirradiated or irradiated larval infections and non-immune mice receiving two superimposed unirradiated infections. An enzyme-linked immunosorbent assay (ELISA) and immunoblotting data suggested that parasite-specific IgG1 was the predominant antibody class in both serum and intestinal perfusates. IgA exhibited differences in antigen specificity between the serum and the intestine. In serum, IgA responses were directed predominantly to L4 somatic antigens, whereas at the mucosal surface they were biased towards L4 excretory/secretory (ES) antigens. No correlation was found between the intensity of the serum or mucosal antibody responses and the mean worm burdens in groups of immune or non-immune mice. Moreover, no correlation was found between levels of parasite-specific serum or mucosal IgG, IgG1, IgG2a or IgA and the loss of worms in individual mice.

Genetic control of immunity to Heligmosomoides polygyrus: fixed H-2 E positive but not H-2 negative cells can present antigen to a parasite-specific T cell hybridoma

A number of T cell hybridomas were produced to adult worm homogenate (AWH) antigen of the nematode parasite Heligmosomoides polygyrus. All of the hybridomas were of the H-2d haplotype and could potentially accept antigen in the context of either the Ad or Ed, H-2 molecules. Three types of antigen presentation were observed, with some of the T cell hybridomas accepting antigen in the context of the E and some in the context of the A molecule. A third type of hybridoma responded to antigen presented by paraformaldehyde fixed APC, but only when APCs were E positive. These same hybridomas, were however, stimulated by AWH, when the antigen was presented by syngeneic but unfixed, E positive or E negative APC. Therefore these data indicate that certain H. polygyrus-specific T cell hybridomas can accept parasite antigen when presented in the context of either the H-2 A or E molecule, but the presentation of antigen by the two different MHC Class II molecules, can apparently utilize differing processing mechanisms.

The role of adult worms in suppressing functional protective immunity to Heligmosomoides polygyrus bakeri challenge infections

Adult Heligmosomoides polygyrus bakeri, radiolabelled with [35S]-methionine were successfully transferred to naive NIH mice by oral gavage. Adult worms and radiolabel could be detected up to 45 days post-infection. Adult worms gavaged into immune NIH mice, immunized with a drug abbreviated larval infection, were rejected within 45 days. These adults worms were unable to ablate the development of a functional protective response to a larval challenge infection in the NIH strain. In fact 50 adult worms were sufficient to significantly immunize NIH mice against a larval challenge infection. However, adult worms were able to suppress the development of a functional protective response in an outbred CFLP strain. Although a protective immune response could not be elicited to a challenge infection in CBA mice, the presence of gavaged adult worms was shown to increase the susceptibility of mice to a challenge infection. For all mouse strains, no significant difference in levels of L4 antigen-specific serum IgG, IgG1, IgG2a, and IgA existed between immune mice and groups of mice immunosuppressed by adult worms. Levels of L4 antigen-specific serum IgG1 were significantly lower in the poorly immunizable CBA strain compared to CFLP and NIH strains. No correlation was found across mouse strains between the intensity of the antibody response and the mean worm burdens per animal group. In addition, no correlation was found between levels of L4 antigen-specific antibody within each mouse and the loss of worms by individual mice.

Genomic variability within laboratory and wild subspecies of Heligmosomoides polygyrus

Genomic DNA extracted from laboratory and wild subspecies of the trichostrongyle nematode Heligmosomoides polygyrus were compared using RFLP and DNA/DNA hybridization techniques. Eight restriction endonuclease digests of the genomic DNA of the two subspecies were hybridized with heterologous ribosomal DNA probes and the total radio-isotope labelled DNA of the laboratory subspecies. DNA hybridization of the two subspecies of H. polygyrus yielded different banding patterns when probed with the rDNA clones in Pvu II digests and when total genomic DNA was used as the probe in Hind III and Pvu II digests. The remaining hybridization profiles of both subspecies were identical.

Immunological relationships during primary infection with Heligmosomoides polygyrus: Th2 cytokines and primary response phenotype

The primary immune response to infection with Heligmosomoides polygyrus was studied in mice differing in response phenotype (fast-SWR, intermediate-NIH, slow-CBA). Marked IgG1 and IgE but not IgG2a antibody responses were detected in infected mice and the former were more intense in fast compared with slow responder strains. Mastocytosis, MMCP-1, and the secretion of cytokines by mesenteric lymph node cells, following stimulation in vitro by Con A, were also more intense initially in SWR mice. Secretion of IL-4 declined in all strains by the 4th week of infection, irrespective of response phenotype. IL-10 was only produced briefly by SWR mice. However, the temporal patterns of secretion of IL-3 and IL-9 clearly distinguished fast from slow responder phenotypes. Following initial intense secretion of IL-3, production declined in all strains but in the 5-6th weeks enhanced secretion was evident in SWR and NIH mice and was sustained until week 10 p.i. In contrast, CBA mice never recovered from the initial down-regulation in weeks 3-4 and secretion declined to background levels by week 6 p.i. despite the continued presence of adult worms. Temporal changes in the secretion of IL-9 were very similar: secretion declined in CBA mice by week 6 p.i., whilst SWR and NIH mice continued to secrete high amounts. We suggest that fast and slow responder mice differ not only in their initial responsiveness to parasite antigens but also in their ability to sustain a Th2 response to the parasite and we propose that the latter is in part determined by their different susceptibilities to parasite-mediated immunomodulation. Only the fast responder strains can sustain a Th2 response of sufficient intensity to facilitate expulsion of adult worms.

Resistance of the hookworms Ancylostoma ceylanicum and Necator americanus to intestinal inflammatory responses induced by heterologous infection

Experiments were carried out to ascertain whether the acute inflammatory phase of the intestinal response of hamsters to infection with Trichinella spiralis would adversely affect hookworms in concurrently infected animals. The survival and growth of hookworms were unaffected. However, the presence of hookworms reduced the establishment of T. spiralis, the initial growth of female worms and their fecundity. The expulsion of T. spiralis was also significantly slower in concurrently infected animals and there was significant depression of the serum IgG antibody response to muscle stage and adult worm antigens of T. spiralis in concurrently infected animals. These results are discussed in relation to the chronicity of human hookworm infections.

Immunological relationships during primary infection with Heligmosomoides polygyrus. Regulation of fast response phenotype by H-2 and non-H-2 genes

The inheritance of response phenotype to Heligmosomoides polygyrus was investigated in F1 hybrid progeny of fast and slow responder mouse strains. The fast responses of SJL(H-2s) and SWR(H-2q) mice were mediated by dominant genes complementing each other in F1 hybrids which lost worms earlier and produced faster parasite-specific IgG1 antibody responses than either parent. However, the response of F1 hybrids from crosses of C57BL/10 (B10, H-2b) mice with either SJL or SWR differed from that of the parental strains and from each other: (B10 x SWR)F1 lost worms earlier than SWR whilst (B10 x SJL)F1 lost worms later than SJL mice. The F1 progeny of SJL mice with congenic strains B10.G (H-2q) and B10.S (H-2s) lost worms as quickly as SJL. Therefore, the response phenotype mediated by the genome of SJL mice was unaffected by H-2 heterozygosity (with H-2q) or homozygosity (H-2s) despite heterozygosity with B10 background genes, but was slowed significantly by heterozygosity with H-2b. All hybrids involving heterozygosity with B10, irrespective of MHC haplotype or background, failed to clear worms completely, in each case a proportion of mice harbouring residual worm burdens after loss of worms from parental strains.

Social behaviour, stress and susceptibility to infection in house mice (Mus musculus): effects of duration of grouping and aggressive behaviour prior to infection on susceptibility to Babesia microti

Unrelated and initially unfamiliar male CFLP mice, maintained for different periods in groups of 6, differed in both their rate of clearance of Babesia microti and the time taken to reach peak parasitaemia in relation to their aggressive behaviour within groups prior to infection. Males maintained in groups for shorter periods and showing more aggression within their group were slower to clear infection and males showing more marked external evidence of aggressive interaction reached a peak of parasitaemia sooner. Serum IgG and corticosterone analyses were consistent with increased aggression causing stress-induced immunodepression but relationships with aggression and social status were not simple. Males showing more aggression tended to enter their groups with higher levels of corticosterone and, to a lesser extent, reduced levels of IgG compared with other mice. The results thus suggest that increased susceptibility to disease may be a cost to males aggressively maintaining high social status.

Immunological relationships during primary infection with Heligmosomoides polygyrus (Nematospiroides dubius): parasite specific IgG1 antibody responses and primary response phenotype

IgG1 antibody responses to Heligmosomoides polygyrus were measured in eight mouse strains supporting acute (< 8 weeks, SJL, SWR), intermediate (10-20 weeks, NIH, BALB/c) or chronic (> 25 weeks, C57BL/0, CBA, C3H, AKR) primary infections. Mice supporting acute or intermediate infections produced more intense antibody responses and total serum IgG1 concentrations were higher than in mice tolerating chronic infections. Positive correlations across mouse strains between the intensity of the antibody response and the percentage loss of worms in weeks 6 and 10 were established. No correlation was found between the response within mouse strains and loss of worms by individual mice. Heavy infections gave marginally higher antibody titres than low intensity infections, but few significant differences were detected and it was concluded that infection intensity did not markedly influence the magnitude of the antibody response. Male and female mice responded similarly despite the earlier loss of worms from females. No association was found between the primary response phenotype and recognition of particular antigens in Western blot analysis, nor did intensity of infection or host gender affect recognition. The possibility that immunomodulatory properties of adult worms may have had a differential influence on ability of strains of contrasting response phenotype to mount IgG1 responses was discussed.

Immunological relationships during primary infection with Heligmosomoides polygyrus (Nematospiroides dubius): downregulation of specific cytokine secretion (IL-9 and IL-10) correlates with poor mastocytosis and chronic survival of adult worms

Mice were infected either with Trichinella spiralis (day 0), Heligmosomoides polygyrus (day-14) or concurrently with both species and were killed in groups, together with naïve control mice, on 2 occasions (day 8 and 15 post infection with T. spiralis, corresponding to days 22 and 29 p.i. with H. polygyrus). The expulsion of T. spiralis was slowed significantly in concurrently infected mice and this was associated with a reduced mastocytosis and lower serum mucosal mast cell protease levels. Mesenteric lymph node (MLN) lymphocytes from all three experimental groups secreted IL-3 and IL-4 in copious amounts when stimulated in vitro by Concanavalin A (Con-A), but the secretion of high levels of IL-9 and IL-10 was essentially confined to mice infected with T. spiralis alone. It is suggested that adult H. polygyrus selectively modulate cytokine secretion by Th2 cells within the MLN during infection and that this is brought about as a direct consequence of the mechanism employed by H. polygyrus to depress mucosal inflammatory responses in order to facilitate its own survival.

Dissociation of specific and total IgE antibody responses following repeated low-level infections with Nippostrongylus brasiliensis in rats

IgE, IgG and mast cell responses were studied in rats infected weekly with 10 larvae of Nippostrongylus brasiliensis (NB). Worm recovery at 8 weeks of repeated infections was six-fold greater than that of a single infection with 10 larvae, suggesting the accumulation of worms during the repeated infections. Total serum IgE was increased after 2 weeks of infection, and further increased after repeated infections: at 6 weeks of infection the level was four to six times higher than that after a single infection. Anti-NB IgG1 levels were also significantly higher after repeated infections than after a single infection. On the other hand, there was no significant difference in the level of anti-NB IgE between single and repeated infections, as determined by ELISA, as well as by passive cutaneous anaphylaxis (PCA) reaction. Mastocytosis was induced in the small intestine after both single and repeated infections, but the levels did not differ between the two. These results indicate that total IgE and specific IgG1 production are augmented by repeated helminth infections, but specific IgE and mast cell responses are not. This pattern of response may minimize the development of IgE-dependent hypersensitivity reactions with repeated helminth infections.