Characterization of the Pelodiscus sinensis polymeric immunoglobulin receptor (P. sinensis pIgR) and its response to LPS and Aeromonas sobria.

Abstract The polymeric immunoglobulin receptor (pIgR) is one of the most vital components of mucosal immunity that plays a pivotal role in mediating transcytosis of polymeric immunoglobulin (pIg) on epithelial surfaces for protection against invading pathogens. Herein, we cloned the full-length cDNA of Pelodiscus sinensis pIgR, designated as P. sinensis pIgR, made of an open reading frame (ORF) of 1848 bp, molecular weight of 68.2 kDa and estimated isoelectric point of 7.00. The deduced P. sinensis pIgR sequence had a leader peptide, extracellular region containing four immunoglobulin-like domains (Ig like domains), transmembrane and intracellular regions comparable with other vertebrates. P. sinensis pIgR contained four Ig like domains that corresponded with mammalian D1, D3, D4 and D5 similar with reptile and avian Ig like domains. It had 43 potential phosphorylation sites, four putative N-glycosylation sites and several motifs resembling mammalian pIgR motifs. Phylogenetic analysis showed a close relationship between P. sinensis pIgR with avian and reptile pIgRs. P. sinensis pIgR basal levels were higher in the esophagus, small intestine and intestinnum crissum than in other organs of health turtles. Intragastric delivery of LPS and Aeromonas sorbia led to significant upregulation of P. sinensis pIgR in tissues of the gastrointestinal tract. A polyclonal anti- P. sinensis pIgR antibody produced in rabbit reacted with the recombinant P. sinensis pIgR protein expressed in Escherichia coli in Western blot and showed positive immune staining in the small intestine of turtle exposed to LPS. These studies demonstrate the existence and immune response of P. sinensis pIgR to stimulation in mucosal organs in Chinese soft-shelled turtles.