Expression of the polymeric Immunoglobulin Receptor (pIgR) in mucosal tissues of common carp (Cyprinus carpio L.) J.H.W.M. Rombout a, * ,1 , S.J.L. van der Tuin a,1 , G. Yang a,b , N. Schopman a , A. Mroczek a , T. Hermsen a , J.J. Taverne-Thiele a a Cell Biology and Immunology Group, Department of Animal Sciences, Wageningen University, PO Box 338, 6700 AH Wageningen, The Netherlands b School of Life Sciences, Shandong Normal University, Jinan 250014, China Received 14 November 2007; revised 25 January 2008; accepted 31 January 2008 Available online 8 February 2008 KEYWORDS Polymeric Immunoglobulin Receptor (pIgR); Teleost; Mucosal tissue; In situ hybridisation; RT-PCR Abstract The mucosal immune system seems to be an important defence mechanism for fish but the binding of IgM in mucosal organs is poorly described in fish. In this study the gene encoding the polymeric Immunoglobulin Receptor (pIgR) in carp has been isolated and sequenced from a liver cDNA-library and aligned with other species. The pIgR of carp consists of 2 Ig domains, a transmembrane and an intracellular region, together 327 amino acids. In situ hybridisations with sense and anti-sense DIG-labelled pIgR RNA probes were performed on liver, gut and skin of common carp (Cyprinus carpio L.) and in these organs only anti-sense probes were found to hybridise. In liver the majority of hepatocytes was stained around the nucleus. In gut and skin, staining could be detected around the nucleus of the epithelial cells, but in gut also a subpopulation of lymphoid cells was stained in epithelium and lamina propria. The specific in situ hybridisation of the epithelia and hepatocytes coincides with the in situ binding of FITC-labelled carp IgM to the same cells. RT-PCR results indicate the expression of the pIgR gene in all lymphoid organs of carp, but not in muscle. Macrophages/neutrophils enriched by adherence or sorted B cells (MACS) did not show expression of the pIgR gene and are excluded as the pIgR expressing lymphoid cells in the intestine. The relevance of pIgR staining and gene expression in mucosal organs is discussed. ª 2008 Elsevier Ltd. All rights reserved. Introduction An important criterion for the existence of a mucosal immune system is the secretion of antigen-specific anti- bodies at mucosal surfaces [1,2], which are continuously exposed to antigens. The first line of immunological * Corresponding author. Tel.: þ31 317 482 729; fax: þ31 317 483 955. E-mail address: jan.rombout@wur.nl (J.H.W.M. Rombout). 1 Both authors contributed equally to this paper. 1050-4648/$ - see front matter ª 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.fsi.2008.01.016 available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/fsi Fish & Shellfish Immunology (2008) 24, 620e628