Available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/devcompimm IgX antibodies in the urodele amphibian Ambystoma mexicanum Be´re´niceSchaerlinger 1 , Jean-Pol Frippiat à EA 3442, Nancy-University, Laboratoire de Biologie Expe´rimentale et Immunologie, Groupe De´veloppement et Immunoge´ne´tique. Boulevard des Aiguillettes, BP 239. F-54506 Vandoeuvre-le`s-Nancy Cedex, France Received 2 August 2007; received in revised form 8 January 2008; accepted 9 January 2008 KEYWORDS Comparative immunology; Evolution; Immunoglobulin; Isotype; Antibody phylogeny; Amphibian Summary Until recently, it was believed that urodele amphibians are able to synthesize only two immunoglobulin isotypes, IgM and IgY. We reinvestigated this issue in the Iberian ribbed newt Pleurodeles waltl and reported recently that this urodele expresses at least three isotypes: IgM, IgP and IgY. In this study, we demonstrate that another urodele, Ambystoma mexicanum, has also a third isotype whose amino acid sequence presents the highest homology with the amino acid sequence of Xenopus IgX. This isotype has typical Ig H-chain characteristics, could form multimers and is mainly expressed in mucosal tissues thereby indicating that it is likely the physiological counterpart of Xenopus IgX and mammalian IgA. Interestingly, no IgP could be found in A. mexicanum, in contrast to P. waltl, in which IgX was not found in previous investigations. These data indicate, for the first time, that different families of urodeles can express different immunoglobulin isotypes. & 2008 Elsevier Ltd. All rights reserved. Introduction The humoral immune system of gnathostome vertebrates is characterized by the production of antibodies (Ab) in response to antigens (Ag). Antibodies are secreted or expressed as membrane-bound forms on the surface of B lymphocytes. Antibodies are made of heavy and light chains. Each chain is composed of a single variable domain at the N-terminal end followed by one or several constant domains. The constant domains of Ig heavy chains define the isotype and determine the physiological function of the Ab. Mammals produce five Ig isotypes (IgA, IgD, IgE, IgG and IgM) that display distinct biological effector functions. IgA is an abundant antibody that mediates immune protection at mucosal surfaces as well as in the serum [1]. Serum IgA is predominantly monomeric while secretory IgA exists as dimeric or higher polymeric forms containing a cysteine-rich polypeptide termed J chain and an additional polypeptide called secretory component (SC) [2,3]. The SC is believed to ARTICLE IN PRESS 0145-305X/$ - see front matter & 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.dci.2008.01.001 à Corresponding author. Tel.: +333 83684494; fax: +333 83684196. E-mail address: Jean-Pol.Frippiat@scbiol.uhp-nancy.fr (J.-P. Frippiat). 1 Present address: EA3446, Nancy-University. Boulevard des Aiguillettes, BP 239. F-54506 Vandoeuvre-le `s-Nancy cedex, France. Developmental and Comparative Immunology (]]]]) ], ]]]–]]] Please cite this article as: Schaerlinger B, Frippiat J-P. IgX antibodies in the urodele amphibian Ambystoma mexicanum. Dev Comp Immunol (2008), doi:10.1016/j.dci.2008.01.001