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FVB/N mice are highly resistant to primary infection with Nippostrongylus brasiliensis

Published online by Cambridge University Press:  07 January 2009

M. L. KNOTT ,
S. P. HOGAN ,
H. WANG ,
K. I. MATTHAEI  and
L. A. DENT
M. L. KNOTT
Affiliation:
School of Molecular and Biomedical Science, University of Adelaide, Adelaide, South Australia, 5005, Australia
S. P. HOGAN
Affiliation:
Cincinnati Children's Hospital Medical Center, Department of Allergy and Immunology, University of Cincinnati College of Medicine, Cincinnati, Ohio45229, USA
H. WANG
Affiliation:
School of Molecular and Biomedical Science, University of Adelaide, Adelaide, South Australia, 5005, Australia
K. I. MATTHAEI
Affiliation:
Division of Molecular Bioscience, John Curtin School of Medical Research, The Australian National University, Canberra, Australian Capital Territory, Australia, 0200
L. A. DENT*
Affiliation:
School of Molecular and Biomedical Science, University of Adelaide, Adelaide, South Australia, 5005, Australia
*
*Corresponding author: School of Molecular and Biomedical Science, University of Adelaide, Adelaide, South Australia, 5005, Australia. Tel: +61 8 83034155. Fax: +61 8 8303 4362. E-mail: lindsay.dent@adelaide.edu.au
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Summary

Nippostrongylus brasiliensis larvae are particularly susceptible to immunological attack during the pre-lung stage of primary and secondary infections in mice. Whilst most of the common laboratory strains of mice are permissive hosts for the parasite, in this study we report for the first time, the strong resistance of naïve FVB/N mice to N. brasiliensis. Damage to larvae is evident within the first 24 h of infection and this may be critical to later larval development and reproductive success. Inflammatory responses in the skin, and larval escape from this tissue were comparable in susceptible CBA/Ca and resistant FVB/N mice, with most larvae exiting within 4 h of a primary infection. Lung larval burdens were also similar between strains, but larvae recovered from FVB/N mice were smaller and less motile. In FVB/N mice, larval colonization of the gut was impaired and worms produced very few eggs. However FVB/N mice did not show enhanced resistance to Heligmosomoides bakeri (also known as Heligmosomoides polygyrus), a nematode largely restricted to the gut. Damage done in the pre-lung or lung stages of infection with N. brasiliensis is likely to contribute to ongoing developmental and functional abnormalities, which are profoundly evident in the gut phase of infection.

Keywords

FVB/N mouseNippostrongylus brasiliensisHeligmosomoides bakeriHeligmosomoides polygyrusprimary resistance
Type
Research Article
Information
Parasitology , Volume 136 , Issue 1 , January 2009 , pp. 93 - 106
Copyright
Copyright © 2009 Cambridge University Press

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References

REFERENCES

Artis, D., Wang, M. L., Keilbaugh, S. A., He, W., Brenes, M., Swain, G. P., Knight, P. A., Donaldson, D. D., Lazar, M. A., Miller, H. R., Schad, G. A., Scott, P. and Wu, G. D. (2004). RELMbeta/FIZZ2 is a goblet cell-specific immune-effector molecule in the gastrointestinal tract. Proceedings of the National Academy of Sciences, USA 101, 13596–13600.CrossRefGoogle ScholarPubMed
Behm, C. A. and Ovington, K. S. (2000). The role of eosinophils in parasitic helminth infections: insights from genetically modified mice. Parasitology Today 16, 202–209.CrossRefGoogle ScholarPubMed
Behnke, J. M., Iraqi, F., Menge, D., Baker, R. L., Gibson, J. and Wakelin, D. (2003 a). Chasing the genes that control resistance to gastrointestinal nematodes. Journal of Helminthology 77, 99–110.CrossRefGoogle ScholarPubMed
Behnke, J. M., Iraqi, F. A., Mugambi, J. M., Clifford, S., Nagda, S., Wakelin, D., Kemp, S. J., Baker, R. L. and Gibson, J. P. (2006 a). High resolution mapping of chromosomal regions controlling resistance to gastrointestinal nematode infections in an advanced intercross line of mice. Mammalian Genome 17, 584–597.CrossRefGoogle Scholar
Behnke, J. M., Lowe, A., Clifford, S. and Wakelin, D. (2003 b). Cellular and serological responses in resistant and susceptible mice exposed to repeated infection with Heligmosomoides polygyrus bakeri. Parasite Immunology 25, 333–340.CrossRefGoogle ScholarPubMed
Behnke, J. M., Mugambi, J. M., Clifford, S., Iraqi, F. A., Baker, R. L., Gibson, J. P. and Wakelin, D. (2006 b). Genetic variation in resistance to repeated infections with Heligmosomoides polygyrus bakeri, in inbred mouse strains selected for the mouse genome project. Parasite Immunology 28, 85–94.CrossRefGoogle ScholarPubMed
Behnke, J. M. and Wahid, F. N. (1991). Immunological relationships during primary infection with Heligmosomoides polygyrus (Nematospiroides dubius): H-2 linked genes determine worm survival. Parasitology 103, 157–164.CrossRefGoogle ScholarPubMed
Ben-Smith, A., Lammas, D. A. and Behnke, J. M. (2002). Effect of oxygen radicals and differential expression of catalase and superoxide dismutase in adult Heligmosomoides polygyrus during primary infections in mice with differing response phenotypes. Parasite Immunology 24, 119–129.CrossRefGoogle ScholarPubMed
Ben-Smith, A., Lammas, D. A. and Behnke, J. M. (2003). 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. Journal of Helminthology 77, 133–146.CrossRefGoogle ScholarPubMed
Cable, J., Harris, P. D., Lewis, J. W. and Behnke, J. M. (2006). Molecular evidence that Heligmosomoides polygyrus from laboratory mice and wood mice are separate species. Parasitology 133, 111–122.CrossRefGoogle ScholarPubMed
Crawford, C., Behnke, J. M. and Pritchard, D. I. (1989). Suppression of heterologous immunity by Nematospiroides dubius antigens in vitro. International Journal for Parasitology 19, 29–34.CrossRefGoogle ScholarPubMed
Cywinska, A., Czuminska, K. and Schollenberger, A. (2004). Granulomatous inflammation during Heligmosomoides polygyrus primary infections in FVB mice. Journal of Helminthology 78, 17–24.CrossRefGoogle ScholarPubMed
Daly, C. M. (1999). Immune responses to Nippostrongylus brasiliensis in interleukin-5 transgenic mice. Ph.D. thesis. The University of Adelaide, Australia.Google Scholar
Daly, C. M., Mayrhofer, G. and Dent, L. A. (1999). Trapping and immobilization of Nippostrongylus brasiliensis larvae at the site of inoculation in primary infections of interleukin-5 transgenic mice. Infection and Immunity 67, 5315–5323.CrossRefGoogle ScholarPubMed
Dent, L. A., Daly, C., Geddes, A., Cormie, J., Finlay, D. A., Bignold, L., Hagan, P., Parkhouse, R. M., Garate, T., Parsons, J. and Mayrhofer, G. (1997 b). Immune responses of IL-5 transgenic mice to parasites and aeroallergens Memórias do Instituto Oswaldo Cruz 92 (Suppl. 2), 45–54.CrossRefGoogle ScholarPubMed
Dent, L. A., Daly, C. M., Mayrhofer, G., Zimmerman, T., Hallett, A., Bignold, L. P., Creaney, J. and Parsons, J. C. (1999). Interleukin-5 transgenic mice show enhanced resistance to primary infections with Nippostrongylus brasiliensis but not primary infections with Toxocara canis. Infection and Immunity 67, 989–993.CrossRefGoogle Scholar
Dent, L. A., Munro, G. H., Piper, K. P., Sanderson, C. J., Finlay, D. A., Dempster, R. K., Bignold, L. P., Harkin, D. G. and Hagan, P. (1997 a). Eosinophilic interleukin 5 (IL-5) transgenic mice: eosinophil activity and impaired clearance of Schistosoma mansoni. Parasite Immunology 19, 291–300.CrossRefGoogle ScholarPubMed
Dent, L. A., Strath, M., Mellor, A. L. and Sanderson, C. J. (1990). Eosinophilia in transgenic mice expressing interleukin 5. The Journal of Experimental Medicine 172, 1425–1431.CrossRefGoogle ScholarPubMed
Donskow-Schmelter, K., Doligalska, M., Rzepecka, J. and Jedlina-Panasiuk, L. (2007). Heligmosomoides polygyrus: decreased apoptosis in fast responder FVB mice during infection. Experimental Parasitology 117, 149–156.CrossRefGoogle ScholarPubMed
El-Malky, M., Maruyama, H., Hirabayashi, Y., Shimada, S., Yoshida, A., Amano, T., Tominaga, A., Takatsu, K. and Ohta, N. (2003). Intraepithelial infiltration of eosinophils and their contribution to the elimination of adult intestinal nematode, Strongyloides venezuelensis in mice. Parasitology International 52, 71–79.CrossRefGoogle Scholar
Else, K. and Wakelin, D. (1989). Genetic variation in the humoral immune responses of mice to the nematode Trichuris muris. Parasite Immunology 11, 77–90.CrossRefGoogle Scholar
Enokihara, H., Nagashima, S., Noma, T., Kajitani, H., Hamaguchi, H., Saito, K., Furusawa, S., Shishido, H. and Honjo, T. (1988). Effect of human recombinant interleukin 5 and G-CSF on eosinophil colony formation. Immunology Letters 18, 73–76.CrossRefGoogle ScholarPubMed
Fallon, P. G., Ballantyne, S. J., Mangan, N. E., Barlow, J. L., Dasvarma, A., Hewett, D. R., McIlgorm, A., Jolin, H. E. and McKenzie, A. N. (2006). Identification of an interleukin (IL)-25-dependent cell population that provides IL-4, IL-5, and IL-13 at the onset of helminth expulsion. The Journal of Experimental Medicine 203, 1105–1116.CrossRefGoogle ScholarPubMed
Fallon, P. G., Jolin, H. E., Smith, P., Emson, C. L., Townsend, M. J., Fallon, R. and McKenzie, A. N. (2002). IL-4 induces characteristic Th2 responses even in the combined absence of IL-5, IL-9, and IL-13. Immunity 17, 7–17.CrossRefGoogle ScholarPubMed
Giacomin, P. R., Gordon, D. L., Botto, M., Daha, M. R., Sanderson, S. D., Taylor, S. M. and Dent, L. A. (2008). The role of complement in innate, adaptive and eosinophil-dependent immunity to the nematode Nippostrongylus brasiliensis. Molecular Immunology 45, 446–455.CrossRefGoogle Scholar
Giacomin, P. R., Wang, H., Gordon, D. L., Botto, M. and Dent, L. A. (2005). Loss of complement activation and leukocyte adherence as Nippostrongylus brasiliensis develops within the murine host. Infection and Immunity 73, 7442–7449.CrossRefGoogle ScholarPubMed
Herbert, D. R., Lee, J. J., Lee, N. A., Nolan, T. J., Schad, G. A. and Abraham, D. (2000). Role of IL-5 in innate and adaptive immunity to larval Strongyloides stercoralis in mice. The Journal of Immunology 165, 4544–4551.CrossRefGoogle ScholarPubMed
Iraqi, F. A., Behnke, J. M., Menge, D. M., Lowe, A. M., Teale, A. J., Gibson, J. P., Baker, L. R. and Wakelin, D. R. (2003). Chromosomal regions controlling resistance to gastro-intestinal nematode infections in mice. Mammalian Genome 14, 184–191.CrossRefGoogle ScholarPubMed
Jose, P. J., Griffiths-Johnson, D. A., Collins, P. D., Walsh, D. T., Moqbel, R., Totty, N. F., Truong, O., Hsuan, J. J. and Williams, T. J. (1994). Eotaxin: a potent eosinophil chemoattractant cytokine detected in a guinea pig model of allergic airways inflammation. The Journal of Experimental Medicine 179, 881–887.CrossRefGoogle Scholar
Kay, A. B., Moqbel, R., Durham, S. R., MacDonald, A. J., Walsh, G. M., Shaw, R. J., Cromwell, O. and Mackay, J. (1985). Leucocyte activation initiated by IgE-dependent mechanisms in relation to helminthic parasitic disease and clinical models of asthma. International Archives of Allergy and Applied Immunology 77, 69–72.CrossRefGoogle ScholarPubMed
Knott, M. L., Matthaei, K. I., Giacomin, P. R., Wang, H., Foster, P. S. and Dent, L. A. (2007). Impaired resistance in early secondary Nippostrongylus brasiliensis infections in mice with defective eosinophilopoeisis. International Journal for Parasitology 37, 1367–1378.CrossRefGoogle ScholarPubMed
Lee, J. J. and Lee, N. A. (2005). Eosinophil degranulation: an evolutionary vestige or a universally destructive effector function? Clinical and Experimental Allergy 35, 986–994.CrossRefGoogle ScholarPubMed
Lee, K. J., Park, S. K., Im, J. A., Kim, S. K., Kim, G. H., Kim, G. Y., Yang, E. J. and Ryang, Y. S. (2004). Susceptibility of several strains of mice to Echinostoma hortense infection. The Korean Journal of Parasitology 42, 51–56.CrossRefGoogle ScholarPubMed
Lewis, R., Behnke, J. M., Cassidy, J. P., Stafford, P., Murray, N. and Holland, C. V. (2007). The migration of Ascaris suum larvae, and the associated pulmonary inflammatory response in susceptible C57BL/6j and resistant CBA/Ca mice. Parasitology 134, 1301–1314.CrossRefGoogle ScholarPubMed
Lewis, R., Behnke, J. M., Stafford, P. and Holland, C. V. (2006). The development of a mouse model to explore resistance and susceptibility to early Ascaris suum infection. Parasitology 132, 289–300.CrossRefGoogle ScholarPubMed
Loke, P., Nair, M. G., Parkinson, J., Guiliano, D., Blaxter, M. and Allen, J. E. (2002). IL-4 dependent alternatively-activated macrophages have a distinctive in vivo gene expression phenotype. BMC Immunology 3, 7.CrossRefGoogle ScholarPubMed
Lopez, A. F., Begley, C. G., Williamson, D. J., Warren, D. J., Vadas, M. A. and Sanderson, C. J. (1986). Murine eosinophil differentiation factor. An eosinophil-specific colony-stimulating factor with activity for human cells. The Journal of Experimental Medicine 163, 1085–1099.CrossRefGoogle ScholarPubMed
Matthaei, K. I., Foster, P. and Young, I. G. (1997). The role of interleukin-5 (IL-5) in vivo: studies with IL-5 deficient mice. Memórias do Instituto Oswaldo Cruz 92 Suppl 2, 63–68.CrossRefGoogle ScholarPubMed
McCormick, M. L., Metwali, A., Railsback, M. A., Weinstock, J. V. and Britigan, B. E. (1996). Eosinophils from schistosome-induced hepatic granulomas produce superoxide and hydroxyl radical. The Journal of Immunology 157, 5009–5015.CrossRefGoogle ScholarPubMed
Meeusen, E. N. and Balic, A. (2000). Do eosinophils have a role in the killing of helminth parasites? Parasitology Today 16, 95–101.CrossRefGoogle ScholarPubMed
Menge, D. M., Behnke, J. M., Lowe, A., Gibson, J. P., Iraqi, F. A., Baker, R. L. and Wakelin, D. (2003). Mapping of chromosomal regions influencing immunological responses to gastrointestinal nematode infections in mice. Parasite Immunology 25, 341–349.CrossRefGoogle ScholarPubMed
Mishra, A., Hogan, S. P., Brandt, E. B., Wagner, N., Crossman, M. W., Foster, P. S. and Rothenberg, M. E. (2002). Enterocyte expression of the eotaxin and interleukin-5 transgenes induces compartmentalized dysregulation of eosinophil trafficking. The Journal of Biological Chemistry 277, 4406–4412.CrossRefGoogle ScholarPubMed
Nabarra, B., Mulotte, M., Casanova, M., Godard, C. and London, J. (2001). Ultrastructural study of the FVB/N mouse thymus: presence of an immature epithelial cell in the medulla and premature involution. Developmental and Comparative Immunology 25, 231–243.CrossRefGoogle ScholarPubMed
Nair, M. G., Guild, K. J. and Artis, D. (2006). Novel effector molecules in type 2 inflammation: lessons drawn from helminth infection and allergy. The Journal of Immunology 177, 1393–1399.CrossRefGoogle ScholarPubMed
Nakamura-Uchiyama, F., Nagao, T., Obara, A., Ishiwata, K. and Nawa, Y. (2001). Natural resistance of 129/SvJ mice to Strongyloides venezuelensis infection. Parasite Immunology 23, 659–663.CrossRefGoogle ScholarPubMed
Outteridge, P. M., Andersson, L., Douch, P. G., Green, R. S., Gwakisa, P. S., Hohenhaus, M. A. and Mikko, S. (1996). The PCR typing of MHC-DRB genes in the sheep using primers for an intronic microsatellite: application to nematode parasite resistance. Immunology and Cell Biology 74, 330–336.CrossRefGoogle ScholarPubMed
Ovington, K. S., McKie, K., Matthaei, K. I., Young, I. G. and Behm, C. A. (1998). Regulation of primary Strongyloides ratti infections in mice: a role for interleukin-5. Immunology 95, 488–493.CrossRefGoogle ScholarPubMed
Pritchard, D. I., Ali, N. M. and Behnke, J. M. (1984). Analysis of the mechanism of immunodepression following heterologous antigenic stimulation during concurrent infection with Nematospiroides dubius. Immunology 51, 633–642.Google ScholarPubMed
Pritchard, D. I. and Behnke, J. M. (1985). The suppression of homologous immunity by soluble adult antigens of Nematospiroides dubius. Journal of Helminthology 59, 251–256.CrossRefGoogle ScholarPubMed
Reece, J. J., Siracusa, M. C. and Scott, A. L. (2006). Innate immune responses to lung-stage helminth infection induce alternatively activated alveolar macrophages. Infection and Immunity 74, 4970–4981.CrossRefGoogle ScholarPubMed
Rothenberg, M. E., Luster, A. D. and Leder, P. (1995). Murine eotaxin: an eosinophil chemoattractant inducible in endothelial cells and in interleukin 4-induced tumor suppression. Proceedings of the National Academy of Sciences, USA 92, 8960–8964.CrossRefGoogle ScholarPubMed
Sasaki, O., Sugaya, H., Ishida, K. and Yoshimura, K. (1993). Ablation of eosinophils with anti-IL-5 antibody enhances the survival of intracranial worms of Angiostrongylus cantonensis in the mouse. Parasite Immunology 15, 349–354.CrossRefGoogle ScholarPubMed
Sheridan, J. W. and Finlay-Jones, J. J. (1977). Studies on a fractionated murine fibrosarcoma: a reproducible method for the cautious and a caution for the unwary. Journal of Cellular Physiology 90, 535–552.CrossRefGoogle Scholar
Stear, M. J., Hetzel, D. J., Brown, S. C., Gershwin, L. J., Mackinnon, M. J. and Nicholas, F. W. (1990). The relationships among ecto- and endoparasite levels, class I antigens of the bovine major histocompatibility system, immunoglobulin E levels and weight gain. Veterinary Parasitology 34, 303–321.CrossRefGoogle ScholarPubMed
Su, Z. and Dobson, C. (1997). H-2 genes and resistance to infection with Heligmosomoides polygyrus in selectively bred mice. International Journal for Parasitology 27, 595–600.CrossRefGoogle ScholarPubMed
Takamoto, M., Ovington, K. S., Behm, C. A., Sugane, K., Young, I. G. and Matthaei, K. I. (1997). Eosinophilia, parasite burden and lung damage in Toxocara canis infection in C57Bl/6 mice genetically deficient in IL-5. Immunology 90, 511–517.CrossRefGoogle ScholarPubMed
Taketo, M., Schroeder, A. C., Mobraaten, L. E., Gunning, K. B., Hanten, G., Fox, R. R., Roderick, T. H., Stewart, C. L., Lilly, F., Hansen, C. T. and et al. (1991). FVB/N: an inbred mouse strain preferable for transgenic analyses. Proceedings of the National Academy of Sciences, USA 88, 2065–2069.CrossRefGoogle ScholarPubMed
Urban, J. F. Jr., Noben-Trauth, N., Donaldson, D. D., Madden, K. B., Morris, S. C., Collins, M. and Finkelman, F. D. (1998). IL-13, IL-4Ralpha, and Stat6 are required for the expulsion of the gastrointestinal nematode parasite Nippostrongylus brasiliensis. Immunity 8, 255–264.CrossRefGoogle ScholarPubMed
Urban, J. F. Jr., Noben-Trauth, N., Schopf, L., Madden, K. B. and Finkelman, F. D. (2001). Cutting edge: IL-4 receptor expression by non-bone marrow-derived cells is required to expel gastrointestinal nematode parasites. The Journal of Immunology 167, 6078–6081.CrossRefGoogle ScholarPubMed
Urban, J. F. Jr., Schopf, L., Morris, S. C., Orekhova, T., Madden, K. B., Betts, C. J., Gamble, H. R., Byrd, C., Donaldson, D., Else, K. and Finkelman, F. D. (2000). Stat6 signaling promotes protective immunity against Trichinella spiralis through a mast cell- and T cell-dependent mechanism. The Journal of Immunology 164, 2046–2052.CrossRefGoogle ScholarPubMed
Voehringer, D., Shinkai, K. and Locksley, R. M. (2004). Type 2 immunity reflects orchestrated recruitment of cells committed to IL-4 production. Immunity 20, 267–277.CrossRefGoogle ScholarPubMed
Wang, M. L., Shin, M. E., Knight, P. A., Artis, D., Silberg, D. G., Suh, E. and Wu, G. D. (2005). Regulation of RELM/FIZZ isoform expression by Cdx2 in response to innate and adaptive immune stimulation in the intestine. American Journal of Physiology. Gastrointestinal and Liver Physiology 288, G1074–G1083.CrossRefGoogle ScholarPubMed
Wassom, D. L. and Kelly, E. A. (1990). The role of the major histocompatibility complex in resistance to parasite infections. Critical Reviews in Immunology 10, 31–52.Google ScholarPubMed
Yamaguchi, Y., Hayashi, Y., Sugama, Y., Miura, Y., Kasahara, T., Kitamura, S., Torisu, M., Mita, S., Tominaga, A. and Takatsu, K. (1988 b). Highly purified murine interleukin 5 (IL-5) stimulates eosinophil function and prolongs in vitro survival. IL-5 as an eosinophil chemotactic factor. The Journal of Experimental Medicine 167, 1737–1742.CrossRefGoogle ScholarPubMed
Yamaguchi, Y., Suda, T., Suda, J., Eguchi, M., Miura, Y., Harada, N., Tominaga, A. and Takatsu, K. (1988 a). Purified interleukin 5 supports the terminal differentiation and proliferation of murine eosinophilic precursors. The Journal of Experimental Medicine 167, 43–56.CrossRefGoogle ScholarPubMed
Yoon, B. I., Choi, Y. K., Kim, D. Y., Hyun, B. H., Joo, K. H., Rim, H. J. and Lee, J. H. (2001). Infectivity and pathological changes in murine clonorchiasis: comparison in immunocompetent and immunodeficient mice. The Journal of Veterinary Medical Science 63, 421–425.CrossRefGoogle ScholarPubMed
Yu, C., Cantor, A. B., Yang, H., Browne, C., Wells, R. A., Fujiwara, Y. and Orkin, S. H. (2002). Targeted deletion of a high-affinity GATA-binding site in the GATA-1 promoter leads to selective loss of the eosinophil lineage in vivo. The Journal of Experimental Medicine 195, 1387–1395.CrossRefGoogle ScholarPubMed
Zaiss, D. M., Yang, L., Shah, P. R., Kobie, J. J., Urban, J. F. and Mosmann, T. R. (2006). Amphiregulin, a TH2 cytokine enhancing resistance to nematodes. Science 314, 1746.CrossRefGoogle ScholarPubMed
Zhao, A., McDermott, J., Urban, J. F. Jr., Gause, W., Madden, K. B., Yeung, K. A., Morris, S. C., Finkelman, F. D. and Shea-Donohue, T. (2003). Dependence of IL-4, IL-13, and nematode-induced alterations in murine small intestinal smooth muscle contractility on Stat6 and enteric nerves. The Journal of Immunology 171, 948–954.CrossRefGoogle ScholarPubMed