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IgT, a primitive immunoglobulin class specialized in mucosal immunity

Nature Immunology volume 11, pages 827835 (2010) | Download Citation


Teleost fish are the most primitive bony vertebrates that contain immunoglobulins. In contrast to mammals and birds, these species are devoid of immunoglobulin A (IgA) or a functional equivalent. This observation suggests that specialization of immunoglobulin isotypes into mucosal and systemic responses took place during tetrapod evolution. Challenging that paradigm, here we show that IgT, an immunoglobulin isotype of unknown function, acts like a mucosal antibody. We detected responses of rainbow trout IgT to an intestinal parasite only in the gut, whereas IgM responses were confined to the serum. IgT coated most intestinal bacteria. As IgT and IgA are phylogenetically distant immunoglobulins, their specialization into mucosal responses probably occurred independently by a process of convergent evolution.

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  1. 1.

    & The evolution of adaptive immune systems. Cell 124, 815–822 (2006).

  2. 2.

    et al. Antibody responses of variable lymphocyte receptors in the lamprey. Nat. Immunol. 9, 319–327 (2008).

  3. 3.

    & Origin and evolution of the adaptive immune system: genetic events and selective pressures. Nat. Rev. Genet. 11, 47–59 (2010).

  4. 4.

    Comparative analyses of immunoglobulin genes: surprises and portents. Nat. Rev. Immunol. 2, 688–698 (2002).

  5. 5.

    & The biology of intestinal immunoglobulin A responses. Immunity 28, 740–750 (2008).

  6. 6.

    , & Is Xenopus IgX an analog of IgA? Eur. J. Immunol. 26, 2823–2830 (1996).

  7. 7.

    & Antibody repertoire development in teleosts—a review with emphasis on salmonids and Gadus morhua L. Dev. Comp. Immunol. 30, 57–76 (2006).

  8. 8.

    & Phylogeny of lower vertebrates and their immunological structures. Curr. Top. Microbiol. Immunol. 248, 67–107 (2000).

  9. 9.

    , & Discovery of a unique Ig heavy-chain isotype (IgT) in rainbow trout: Implications for a distinctive B cell developmental pathway in teleost fish. Proc. Natl. Acad. Sci. USA 102, 6919–6924 (2005).

  10. 10.

    , , & The immunoglobulin heavy-chain locus in zebrafish: identification and expression of a previously unknown isotype, immunoglobulin Z. Nat. Immunol. 6, 295–302 (2005).

  11. 11.

    The last flag unfurled? A new immunoglobulin isotype in fish expressed in early development. Nat. Immunol. 6, 229–230 (2005).

  12. 12.

    , & Varied redox forms of teleost IgM: an alternative to isotypic diversity? Immunol. Rev. 166, 133–142 (1998).

  13. 13.

    et al. B lymphocytes from early vertebrates have potent phagocytic and microbicidal abilities. Nat. Immunol. 7, 1116–1124 (2006).

  14. 14.

    & Microfilament and microtubule function in human monocytes. J. Lab. Clin. Med. 90, 737–743 (1977).

  15. 15.

    , , & Characterization of the host response to the myxosporean parasite, Ceratomyxa shasta (Noble), by histology, scanning electron microscope, and immunological techniques. J. Fish Dis. 12, 509–522 (1989).

  16. 16.

    , , & In vivo IgA coating of anaerobic bacteria in human faeces. Gut 38, 348–354 (1996).

  17. 17.

    , & Immune exclusion is a function of IgA. Nature 255, 745–746 (1975).

  18. 18.

    Mucosal immunity: induction, dissemination, and effector functions. Scand. J. Immunol. 70, 505–515 (2009).

  19. 19.

    , , & Intestinal IgA synthesis: a primitive form of adaptive immunity that regulates microbial communities in the gut. Semin. Immunol. 19, 127–135 (2007).

  20. 20.

    , , , & A teleost polymeric Ig receptor exhibiting two Ig-like domains transports tetrameric IgM into the skin. J. Immunol. 178, 5682–5689 (2007).

  21. 21.

    et al. Molecular cloning and functional analysis of polymeric immunoglobulin receptor gene in orange-spotted grouper (Epinephelus coioides). Comp. Biochem. Physiol. 154, 282–289 (2009).

  22. 22.

    & The function of immunoglobulin A in immunity. J. Pathol. 208, 270–282 (2006).

  23. 23.

    , & The IgA system: a comparison of structure and function in different species. Vet. Res. 37, 455–467 (2006).

  24. 24.

    et al. Monoclonal antibodies to lymphocytes of rainbow trout (Oncorhynchus mykiss). Fish Shellfish Immunol. 14, 239–257 (2003).

  25. 25.

    , , , & Monoclonal antibodies recognising serum immunoglobulins and surface immunoglobulin-positive cells of puffer fish, torafugu (Takifugu rubripes). Fish Shellfish Immunol. 17, 211–222 (2004).

  26. 26.

    , , & Evaluation of immune functions of rainbow trout (Oncorhynchus mykiss)—how can environmental influences be detected? Toxicol. Lett. 131, 83–95 (2002).

  27. 27.

    et al. Immunoglobulin D enhances immune surveillance by activating antimicrobial, proinflammatory and B cell-stimulating programs in basophils. Nat. Immunol. 10, 889–898 (2009).

  28. 28.

    , & The gut-associated lymphoid tissue (GALT) of carp (Cyprinus carpio L.): an immunocytochemical analysis. Dev. Comp. Immunol. 17, 55–66 (1993).

  29. 29.

    et al. Phenotypic and functional similarity of gut intraepithelial and systemic T cells in a teleost fish. J. Immunol. 176, 3942–3949 (2006).

  30. 30.

    , , & Plasmablast and plasma cell production and distribution in trout immune tissues. J. Immunol. 173, 7317–7323 (2004).

  31. 31.

    , , , & Ontogeny of the immune system of fish. Fish Shellfish Immunol. 20, 126–136 (2006).

  32. 32.

    , , & Vaccines for fish in aquaculture. Expert Rev. Vaccines 4, 89–101 (2005).

  33. 33.

    , , & Gut immunology in fish: a review. Dev. Comp. Immunol. 12, 453–480 (1988).

  34. 34.

    & B-lymphocyte responses in the large intestine and mesenteric lymph nodes of mice infected with Eimeria falciformis (Apicomplexa). J. Parasitol. 74, 144–152 (1988).

  35. 35.

    , & Coccidiosis: characterization of antibody responses to infection with Eimeria nieschulzi. Parasite Immunol. 6, 1–12 (1984).

  36. 36.

    , & Microbial diversity of intestinal contents and mucus in rainbow trout (Oncorhynchus mykiss). J. Appl. Microbiol. 102, 1654–1664 (2007).

  37. 37.

    , & Homeostasis and inflammation in the intestine. Cell 140, 859–870 (2010).

  38. 38.

    , , & Overview of gut immunology. Adv. Exp. Med. Biol. 635, 1–14 (2008).

  39. 39.

    et al. Conservation of structural and functional features in a primordial CD80/86 molecule from rainbow trout (Oncorhynchus mykiss), a primitive teleost fish. J. Immunol. 183, 83–96 (2009).

  40. 40.

    , , & Spatial and temporal occurrence of the salmonid parasite Ceratomyxa shasta in the Oregon-California Klamath river basin. J. Aquat. Anim. Health 18, 194–202 (2006).

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We thank G. Warr (National Science Foundation) for anti–trout IgM; D. Artis and P. Boudinot for critical reading of the manuscript; the Morphology Core of the Center for Molecular Studies in Digestive and Liver Diseases of the University of Pennsylvania, especially G. Swain, for help and advice on immunohistochemistry; C. Pletcher and the staff of the Flow Cytometry and Cell Sorting Facility of the University of Pennsylvania for cell sorting; and Y. Liu, L. Zhang and C. Zhou for technical assistance in cell transfection and immunofluorescence microscopy analyses. Supported by the National Science Foundation (NSF-MCB-0719599 to J.O.S.), the US National Institutes of Health (R01GM085207-01 to J.O.S.) and the United States Department of Agriculture (USDA-NRI 2006-01619 and USDA-NRI 2007-01719 to J.O.S.).

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Author notes

    • Yong-An Zhang
    •  & Irene Salinas

    These authors equally contributed to this work.


  1. Department of Pathobiology, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA.

    • Yong-An Zhang
    • , Irene Salinas
    • , Jun Li
    • , David Parra
    • , Zhen Xu
    •  & J Oriol Sunyer
  2. Department of Microbiology, Center for Fish Disease Research, Oregon State University, Corvallis, Oregon, USA.

    • Sarah Bjork
    •  & Jerri Bartholomew
  3. Research Division, Clear Springs Foods, Buhl, Idaho, USA.

    • Scott E LaPatra


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Y.-A.Z. purified trout IgT, developed polyclonal and monoclonal antibodies to IgT and a polyclonal antibody to trout pIgR, analyzed the biochemical features of IgT and the gene-expression profiles of IgT+ and IgM+ cells, measured specific IgT and IgM titers to C. shasta and did all experiments involved in cloning and functional studies of trout pIgR; I.S. developed the protocols to obtain leukocytes and bacteria from trout GALT and the immunohistochemistry protocols to detect IgT+ and IgM+ cells and C. shasta in trout lymphoid tissues and did immunohistochemistry studies and flow cytometry of IgT+ and IgM+ cells in trout GALT and gut luminal bacteria; J.L. did the flow cytometry of IgT+ and IgM+ cells of trout lymphoid organs, measured the phagocytotic capacity and intracellular bacterial killing of B cells and contributed to the evaluation of total IgT and IgM concentrations in serum and gut mucus, together with Y.-A.Z.; D.P. analyzed IgT and IgM coating on gut bacteria, did the B cell proliferation studies and tested the production of IgT and IgM after stimulation with microbial products; S.B. infected fish with C. shasta and provided samples from survivor and control fish; Z.X. contributed to the evaluation of the production of IgT and IgM by cultured trout leukocytes and sorted B cells; S.E.L. and J.B. contributed to the experimental design and discussions related to C. shasta infection; J.O.S. designed the overall study, contributed to data analysis and wrote the main body of the paper; and all authors read and commented on the paper. J.L. and D.P. contributed equally to this work.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to J Oriol Sunyer.

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