Effect of host sex on passive immunity in mice infected with Nematospiroides dubius

The Use and Underuse of Model Systems in Infectious Disease Ecology and Evolutionary Biology

AbstractEver since biologists began studying the ecology and evolution of infectious diseases (EEID), laboratory-based model systems have been important for developing and testing theory. Yet what EEID researchers mean by the term "model systems" and what they want from them is unclear. This uncertainty hinders our ability to maximally exploit these systems, identify knowledge gaps, and establish effective new model systems. Here, we borrow a definition of model systems from the biomolecular sciences to assess how EEID researchers are (and are not) using 10 key model systems. According to this definition, model systems in EEID are not being used to their fullest and, in fact, cannot even be considered model systems. Research using these systems consistently addresses only two of the three fundamental processes that underlie disease dynamics-transmission and disease, but not recovery. Furthermore, studies tend to focus on only a few scales of biological organization that matter for disease ecology and evolution. Moreover, the field lacks an infrastructure to perform comparative analyses. We aim to begin a discussion of what we want from model systems, which would further progress toward a thorough, holistic understanding of EEID.

Immunity to the model intestinal helminth parasite Heligmosomoides polygyrus

Heligmosomoides polygyrus is a natural intestinal parasite of mice, which offers an excellent model of the immunology of gastrointestinal helminth infections of humans and livestock. It is able to establish long-term chronic infections in many strains of mice, exerting potent immunomodulatory effects that dampen both protective immunity and bystander reactions to allergens and autoantigens. Immunity to the parasite develops naturally in some mouse strains and can be induced in others through immunization; while the mechanisms of protective immunity are not yet fully defined, both antibodies and a host cellular component are required, with strongest evidence for a role of alternatively activated macrophages. We discuss the balance between resistance and susceptibility in this model system and highlight new themes in innate and adaptive immunity, immunomodulation, and regulation of responsiveness in helminth infection.

A method for estimating possible parasite-related host mortality, illustrated using data from Callitetrarhynchus gracilis (Cestoda: Trypanorhyncha) in lizardfish (Saurida spp.)

The frequency distribution of parasites in hosts commonly follows a negative binomial or similar distribution. Under certain conditions the magnitude of parasite-associated host mortality can be estimated by comparing the tail of the observed distribution to that of the distribution predicted from the first few points of the data. For the technique to work the following assumptions need to be met: mortality in lightly infected fish must be rare; infection and consequent mortality occur only in fish younger than those sampled; and the frequency distribution of the parasite at the time of infection should conform to a known probability distribution. The method was applied to frequency distributions of blastocysts of Callitetra rhynchus gracilis in 898 Saurida tumbil (Bloch) and 5013 S. undosquamis (Richardson). Parasite-associated mortality in S. tumbil was calculated to be at least 11 % in males and 2% in females. For S. undosquamis, estimated mortality was about 5% in males and 3% in females. The numbers of parasites estimated to produce a 0·5 probability of death, the parasitological equivalent of an LD50 were 3·4 and 5·7 for S. tumbil males and females, and 18 and 3 for S. undosquamis males and females respectively.

Effects of three simultaneous demands on glucose transport, resting metabolism and morphology of laboratory mice

In nature, animals must successfully respond to many simultaneous demands from their environment in order to survive and reproduce. We examined physiological and morphological responses of mice given three demands: intestinal parasite infection with Heligmosomoides polygyrus followed by caloric restriction (70% of ad libitum food intake versus ad libitum for 10 days) and/or cold exposure (5 degrees C vs. 23 degrees C for 10 days). We found significant interactions between these demands as well as independent effects. Small intestine structure and function changed with demands in both independent and interactive ways. Body mass decreased during caloric restriction and this decrease was greater for cold-exposed than warm-exposed mice. In ad libitum fed mice, body mass did not change with either cold exposure or parasite infection but body composition (fat versus lean mass of whole body or organs) changed with both demands. Generally, organ masses decreased with caloric restriction (even after accounting for body mass effects) and increased with cold exposure and parasite infection whereas fat mass decreased with both caloric restriction and parasite infection. Mass adjusted resting metabolic rate (RMR) increased with cold exposure, decreased with caloric restriction but, unlike previous studies with laboratory mice, did not change with parasite infection. Our results demonstrate that the ability of mice to respond to a demand is influenced by other concurrent demands and that mice show phenotypic plasticity of morphological and physiological features ranging from the tissue level to the level of the whole organism when given three simultaneous demands.

Maternal and direct effects of the intestinal nematode Heligmosomoides polygyrus on offspring growth and susceptibility to infection

The laboratory mouse (Mus musculus) has a naturally occurring intestinal nematode (Heligmosomoides polygyrus) that induces an immune response, causes phenotypic plasticity in metabolism and in organ structure and function, and results in changes in host reproductive output. The objectives of the present study were to determine (1) whether pups infected with parasites at weaning grew differently and had a different body composition at adulthood compared with uninfected pups, (2) whether offspring from parasitized mothers grew differently and had a different body composition at adulthood compared with offspring from unparasitized mothers, (3) whether parasite effects on body composition of pups varied under different infection intensities and (4) whether maternal parasite infection affected susceptibility, duration and intensity of offspring parasite infection. H. polygyrus had direct and maternal effects on offspring growth, but final adult mass was not affected by parasites. Parasite infection in offspring had no effect on overall fat mass, but mass changes for some organs were greater for mice that had a high infection intensity compared with mice that had a low infection intensity. Only offspring from parasitized mothers cleared their parasite infection; however, if the infection was not cleared, the final infection intensity was greater for offspring born to parasitized mothers than to unparasitized mothers. This study shows that chronic, sublethal parasite infection with H. polygyrus has both maternal and direct effects that induce physiological changes in growing mice sufficient to alter host growth trajectories, morphology and susceptibility to parasite infection.

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.

Influence of sex and reproductive status on susceptibility of ruminants to nematode parasitism

Bulls and rams are notorious among stockmen and stud breeders for their apparently greater susceptibility than cows, ewes, steers or wethers to diseases caused by excessive infection with parasitic nematodes. Extension advice given to farmers generally includes a recommendation to treat entire male animals as though they were weaners. In contrast, the scientific literature contains little documentation of this fact, although the phenomenon has been well-described in laboratory animals. Scientific interest in the susceptibility of lactating cows and especially ewes to nematode parasitism has been more extensive, but unproductive in terms of elucidating responsible mechanisms. Where ewes have acquired immunity to nematode infection, they tend to lose it around the time of parturition and during lactation, with important epidemiological and productivity consequences. In strains of sheep selected for resistance to nematode infection, principally through a more rapidly acquired immune response, resistant ewes still undergo a periparturient loss of immunity but retain their relative superiority over unselected or susceptible ewes. The mechanisms involve effects of hormones associated with lactation on the immune system, but an unequivocal role for prolactin or any other hormone has not yet been identified. Collaboration between immunologists, endocrinologists and parasitologists is required.

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.

Heligmosomoides polygyrus: A model for chronic gastrointestinal helminthiasis

Establishment of chronic infections and strain-dependent variation in resistance to challenge infections are well-known features of the relationship between mice and the intestinal nematode parasite Heligmosomoides polygyrus. Here, Fernando Monroy and Javier Enriquez examine host responses, immunogenic and nonimmunogenic antigens of the parasite, and parasite immune evasion strategies in this useful laboratory mouse model of nematode parasitism of mammals.

Nematospiroides dubius: passive transfer of protective immunity to mice with monoclonal antibodies

Nine hybridoma cell lines secreting monoclonal antibodies specific for Nematospiroides dubius were produced by fusion of the mouse myeloma cell line NS-1 to either spleen cells or mesenteric lymph node cells from mice repeatedly infected with N. dubius. Seven of the antibodies were identified as IgM and two as IgG1. Each monoclonal antibody bound to polypeptide epitopes on both infective larvae (L3) and adult worms. However, five antibodies bound preferentially to L3 and three to adult worms. All nine antibodies reacted with high molecular weight protein antigens. Passive protective immunity in Balb/c mice was demonstrated with monoclonal antibodies Nd2 and Nd3 in ascites fluid which stunted both male and female worms and reduced parasite fecundity.

Surface and excretory/secretory antigens of Nematospiroides dubius

Sera from mice immunized by repeated anthelmintic-terminated infections (IMS) or by a single primary infection (PMS) of Nematospiroides dubius were assayed for antibodies reactive with N. dubius antigens. The surface proteins of adult worms, the excretory/secretory (ES) proteins of adult worms and soluble extracts from lysates of both adult (AWH) and larval (LWH) N. dubius were used in an immunoprecipitation assay. A 60,000 MW protein was the major radiolabelled surface and ES protein. This antigen was dominant in precipitates by IMS from AWH, ES and surface-labelled worms but was not precipitated by PMS from any antigen source. Minor antigens of 20,000, 33,000, 36,000, 45,000, 50,000 and 66,000 MW were precipitated from AWH by both PMS and IMS but not from ES or surface-labelled worms. The dominant antigen precipitated from LWH by IMS was 20,000 MW. This antigen was not precipitated by PMS but larval antigens of 65,000 and 96,000 MW were precipitated by both PMS and IMS. The major antigens precipitated by IMS were adult (60,000 MW) and larvae (20,000 MW) stage-specific but some minor antigens (33,000, 45,000, 50,000 MW) were common to both stages. Our results show that the dominant antigen precipitated by serum immunoglobulin from mice immunized by repeated anthelmintic-terminated infections are proteins present on both the cuticle surface and in the ES.

Mice vaccinated against Nematospiroides dubius with antigens isolated by affinity chromatography from adult worms

A crude soluble extract (AWH) obtained from homogenized adult Nematospiroides dubius worms was fractionated into normal (NMIgAg) and immune (IMIgAg) antigens by sequential passage through Sepharose 4B, and CNBr-activated Sepharose 4B to which immunoglobulins from normal (NMIg) and N. dubius-infected mouse serum (IMIg) had been coupled. Sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) under reducing conditions showed that MNIgAg and IMIgAg contained several proteins with molecular weights (MW) between 20,000 and 200,000. IMIgAg contained 2 polypeptides, MW 24,000 and 55,000, which reacted strongly in western blot analysis against IMIg; the larger molecule related to a cuticular component of the worm. Protective high MW AWH G-200 filtrates shared 5 polypeptides with IMIgAg (MW 85,000-200,000) together with several smaller molecules (MW 30,000-less than 10,000). The MW 55,000 and 24,000 components concentrated in IMIgAg were restricted to non-protective low MW AWH gel filtrates. BCF1 mice vaccinated with IMIgAg were protected against N. dubius. Worm numbers, size and fecundity were reduced to an extent commensurate with that obtained in mice vaccinated with AWH. Mice vaccinated with NMIgAg showed partial resistance. The role of surface and dominant parasite immunogens in immunity is discussed.

Nematospiroides dubius: direct and correlated responses to selection for high and low immune responsiveness in mice

High and low immune responder lines of mice were bred selectively from an allogeneic stock over 10 generations, based on their fecal parasite egg count assayed 3 weeks after reinfection with 100 Nematospiroides dubius larvae. By generation 10, (F10), the low immune response mice voided about 10 times as many fecal N. dubius eggs as the high immune response mice. Realized heritability for the selected trait, fecal egg count after secondary infection (= protective immunity), was 0.35 at F7. F7 was considered the selection limit. Selection for change in fecal egg count did not significantly influence the conformational nor reproductive characteristics of these mice. Significant phenotypic and genetic correlations were evident between the selected character and innate immunity to N. dubius, humoral antibody response to N. dubius infection, and establishment, growth, and reproduction of N. dubius in the selected mice.

Murine malaria: resistance of AXB/BXA recombinant inbred mice to Plasmodium chabaudi

The level of resistance to infection with Plasmodium chabaudi is genetically controlled. We have previously reported that a single dominant gene is responsible for the variation in host resistance to malaria between susceptible A/J- and resistant C57BL-derived mice. In the present study, recombinant inbred strain analysis was performed with AXB/BXA recombinant inbred strains derived from A/J and C57BL/6 progenitors. Typing of 17 AXB/BXA recombinant inbred strains confirmed the unigenic control of inheritance in this particular strain combination and allowed us to demonstrate genetic linkage between the traits of resistance (defined as a prolonged survival and a low peak parasitemia) and the magnitude of splenomegaly. The influence of sex on the course of infection, which we previously reported in the examination of segregating populations (Stevenson et al., Infect. Immun. 38:80-88, 1982), was again demonstrated in the survey of RI strains.

Biochemical and physiological effects of metazoan endoparasites on their host species

1. The integrative nature of the parasite-host association was discussed, specifically with regard to the metabolic effects of parasitization as well as the physiological manifestation of infection in relation to the host's nutritional physiology. Endocrine interactions were also considered. 2. Relationships involving parasitic insects, including members of the orders Diptera, Hymenoptera and Strepsiptera, parasitic helminths, including members of the phyla Acanthocephala and Nematoda and the classes Cestoidea and Trematoda of the Platyhelminthes, as well as parasitic crustaceans in association with their invertebrate and/or vertebrate, intermediate, paratenic as well as definitive hosts were considered. 3. A broad conceptual or "topic" approach to understanding symbiotic relationships was emphasized. De-emphasis of descriptive categorization and the use of benefit/harm as criteria characterizing parasitic relationships was suggested. 4. The hypothetical concept of host regulation was briefly examined and the use of anthropometric descriptors such as "beneficial" and "harmonious" in parasitology discussed.

Influence Of Transferred Anti-Nematospiroides Dubius Immune Serum And Igg On Immune Reaction In Recipient Mice

The effect of transferred immune serum and IgG on the response of recipient mice to concurrent infections with larvae has been investigated. Following one infection, recipient mice harboured fewer worms than control mice, the worms were stunted and thier fecundities were greatly reduced. Four concurrent infections was found to reduce worm burden and worm fecundity, and induce an increase of serum antibody titers in no-treatment and normal serum given mice. On the other hand the transferred immune serum and IgG appeared to adversely affect the protective immune response in recipient mice. In recipient mice, worm fecundity was consistently increased throughout experiment and harboured more worms after four infections than control mice. Serum anti-N. dubius antibody titers of mice made passively immune by transfer of immune serum and IgG were not significant difference between one infection and four infections. Thus, transferred immune serum and IgG may debilitate host antibody production.

Murine malaria: genetic control of resistance to Plasmodium chabaudi

Strain variation in the level of resistance to malaria was investigated in inbred strains of mice after infection with Plasmodium chabaudi. When infected intraperitoneally with 10(6) P. chabaudi-parasitized erythrocytes, mice of 11 inbred strains could be separated into two groups by using survival time as the criterion; C57BL/6J, C57L/J, DBA/2J, CBA/J, and B10.A/SgSn mice were found to be resistant to P. chabaudi, whereas A/J, DBA/1J, BALB/c, C3H/HeJ, AKR/J, and SJL/J mice were susceptible. An examination of F1 hybrids revealed that resistance was dominant over susceptibility. A segregation analysis of backcross and F2 progeny derived from susceptible A/J and resistant B10.A/SgSn parental mice suggested that host resistance in this strain combination was genetically controlled by a single, dominant, non-H-2-linked gene. Inheritance of resistance was autosomal, but expression of the trait was influenced by the sex of the host, female mice being more resistant than male mice. Phenotypic expression of the resistance gene was apparent within 6 days of infection as a significant difference between resistant and susceptible mice in the level of parasitemia. A preliminary analysis of the mechanism of resistance showed that compared with susceptible A/J mice, resistant B10.A/SgSn hosts had an augmented erythropoietic response during the course of malaria, as well as phenylhydrazine-induced anemia. These results suggest that the ability to replace destroyed erythrocytes quickly and efficiently may determine host survival after infection with P. chabaudi.

Genetic control of resistance to infection with Nematospiroides dubius in mice: selection of high and low immune responder populations of mice

F1, Quackenbush (Q) x Wild (W) Mus musculus were assayed and selected for their level of immunity to secondary infections with 100 Nematospiroides dubius using faecal parasite egg counts. A significant positive linear correlation was found between the number of parasite eggs voided in the faeces and the number of N. dubius recovered after secondary infections in mice. Selection for immunity was not influenced by the conformation of the mice. High (H) and low (L) responder colonies together with a randomly (Rd) bred colony of mice were established over 5 generations. Adaptive immunity was more efficacious in protecting female than male mice and appeared to be controlled by a few dominant genes; the heritability (h2) of the trait was estimated at 0.56 for the parental stock and 0.55 for the F5 Rd colony and the realized heritability was 0.49. Higher anti-N. dubius antibody titres were detected in H than L mice. H mice harboured fewer and less fecund parasites than Rd colony mice; L mice had more worms with greater fecundities than Rd mice. The levels of primary infections in H and L mice related to the levels developed after secondary infection from F4. This suggested at least partial linkage of genes controlling innate with genes controlling adaptive immunity against N. dubius.

Cellular immunity to encephalitogenic peptide in tumour-bearing mice

Mice bearing a methylcholanthrene-induced tumour were tested for their cell mediated reactivity to the experimental allergic encephalomyelitis (EAE) peptide of human myelin basic protein (MBP) in the leucocyte adherence inhibition (LAI) test. Tested over a range of peptide concentrations, peritoneal cells (PC) from tumour-bearing mice exhibited optimal adherence inhibition at 640 ng/ml; PC from normal and parasite-infected mice were unreactive. The EAE peptide also stimulated PC from tumour-bearing mice in the E-rosette augmentation (ERA) test and in the macrophage migration inhibition (MMI) test. MMI appeared to be the most sensitive assay, in that significant reaction at peptide concentrations well below those giving significant LAI and ERA. LAI reactivity to the peptide was detected 5 days after tumour transplantation, and continued to be detectable even with very large tumours. In vitro assays were confirmed by demonstration of EAE peptide recognition in vivo, in tumour-bearing and tumour-excised mice, using the delayed-type hypersensitivity reaction. The present experiments demonstrate an antigenic determinant in murine tumours, similar to the well-characterized EAE peptide of human MBP, and establish an animal model for study and characterization of common tumour-associated antigens.

Passive immunity in rats infected with Angiostrongylus cantonensis: interactions between syngeneic immune serum and sensitized lymph node cells

Immune serum injected into the peritoneum of rats passively protected them against Angiostrongylus cantonensis; this protection was greater than that conferred by passively transferred immune lymph node cells. When immune lymph node cells and serum were transferred together into the same rat, no enhanced protection was observed. The protective effect of serum was inhibited by the lymph node cells to levels commensurate with those conferred by immune lymph node cells alone. Normal lymph node cells also depressed the levels of immunity conferred by immune serum when they were transferred together with serum, but to a lesser extent than did sensitized lymph node cells. Transferred antibody acted to suppress antibody production against A. cantonensis in recipient rats.

Genetic control of liability to infection with Nematospiroides dubius in mice: selection of refractory and liable populations of mice

Quackenbush strain and wild Mus musculus were assayed for their liability to primary infection with 100 L3 Nematospiroides dubius using an experimentally derived selection index. Refractory and liable colonies of mice were established over 5 generations. Liability to N. dubius infection was found likely to be controlled by several genes; the heritability (h2) of this trait was estimated at 0.45. Positive linear correlation was found between the number of parasite eggs voided and the number of adult N. dubius recovered, negative correlation between the pre-patent period of infection in days and the number of parasite eggs voided and positive correlation in 2 of 5 generations between live mouse body weight and the number of adult N. dubius recovered. Further, positive correlation was found between the liability of female mice to N. dubius and their progeny litter size number. The genetic mechanisms controlling the liability trait and the possible evolutionary significance of these results are discussed.