Expression and functional analysis of polymeric immunoglobulin receptor in Nile tilapia (Oreochromis niloticus)

Polymeric immunoglobulin receptor (pIgR) plays important roles in transport of polymeric immunoglobulins across mucosal epithelial cells and prevention of access of pathogens into the organisms. In this study, a pIgR ortholog (OnpIgR) was cloned and identified from Nile tilapia (Oreochromis niloticus). The open reading frame (ORF) of OnpIgR is 1023 bp, encoding a predicted protein of 341 amino acids. The deduced amino acid sequence of OnpIgR is highly homologous to other teleost's pIgRs, containing two Ig-like domains (ILDs), a transmembrane region and an intracellular region. Expression analysis revealed that OnpIgR was exhibited in all tested tissues including liver, spleen, skin and intestines, and highly expressed in the liver. Immunofluorescence detection indicated that the natural pIgR expressed on the membrane of the epithelial cells. After challenge of bacterial pathogen (Streptococcus agalactiae), OnpIgR expression was significantly up-regulated in intestines and skin, as well as intestinal epithelial cells. In addition, recombinant OnIFN-γ induced the expression of pIgR in the intestinal epithelial cells. Moreover, recombinant OnpIgR protein was able to bind both S. agalactiae and A. hydrophila in vitro, and interact with (r)OnIgM and (r)OnIgT. Taken together, the results indicated that OnpIgR, involving in the polymeric immunoglobulin transport, might play an important role in mucosal immunity against bacterial infection.