Identification of a Polymeric Ig Receptor Binding Phage-displayed Peptide That Exploits Epithelial Transcytosis without Dimeric IgA Competition

Abstract

The polymeric Ig receptor (pIgR), also called membrane secretory component (SC), mediates epithelial transcytosis of polymeric immunoglobulins (pIgs). J Chain-containing polymeric IgA (pIgA) and pentameric IgM bind pIgR at the basolateral epithelial surface. After transcytosis, the extracellular portion of the pIgR is cleaved at the apical side, either complexed with pIgs as bound SC or unoccupied as free SC. This transport pathway may be exploited to target bioactive molecules to the mucosal surface. To identify small peptide motifs with specific affinity to human pIgR, we used purified free SC and selection from randomized, cysteine-flanked 6- and 9-mer phage-display libraries. One of the selected phages, called C9A, displaying the peptide CVVWMGFQQVC, showed binding both to human free SC and SC complexed with pIgs. However, the pneumococcal surface protein SpsA (Streptococcus pneumoniae secretory IgA-binding protein), which binds human SC at a site distinct from the pIg binding site, competed with the C9A phage for binding to SC. The C9A phage showed greatly increased transport through polarized Madin-Darby canine kidney cells transfected with human pIgR. This transport was not affected by pIgA nor did it inhibit pIgR-mediated pIgA transcytosis. A free peptide of identical amino acid sequence as that displayed by the C9A phage inhibited phage interaction with SC. This implied that the C9A peptide sequence may be exploited for pIgR-mediated epithelial transport without interfering with secretory immunity. The polymeric Ig receptor (pIgR), also called membrane secretory component (SC), mediates epithelial transcytosis of polymeric immunoglobulins (pIgs). J Chain-containing polymeric IgA (pIgA) and pentameric IgM bind pIgR at the basolateral epithelial surface. After transcytosis, the extracellular portion of the pIgR is cleaved at the apical side, either complexed with pIgs as bound SC or unoccupied as free SC. This transport pathway may be exploited to target bioactive molecules to the mucosal surface. To identify small peptide motifs with specific affinity to human pIgR, we used purified free SC and selection from randomized, cysteine-flanked 6- and 9-mer phage-display libraries. One of the selected phages, called C9A, displaying the peptide CVVWMGFQQVC, showed binding both to human free SC and SC complexed with pIgs. However, the pneumococcal surface protein SpsA (Streptococcus pneumoniae secretory IgA-binding protein), which binds human SC at a site distinct from the pIg binding site, competed with the C9A phage for binding to SC. The C9A phage showed greatly increased transport through polarized Madin-Darby canine kidney cells transfected with human pIgR. This transport was not affected by pIgA nor did it inhibit pIgR-mediated pIgA transcytosis. A free peptide of identical amino acid sequence as that displayed by the C9A phage inhibited phage interaction with SC. This implied that the C9A peptide sequence may be exploited for pIgR-mediated epithelial transport without interfering with secretory immunity. Mucosal epithelia form a barrier between the interior of the body and the external environment. At least 80% of all antibody-producing plasma cells of the body are located in the gastrointestinal and respiratory mucosae, and most of them are committed to production of dimers and larger polymers of IgA, collectively called pIgA 5The abbreviations used are: pIgA, polymeric IgA; pIgR, polymeric Ig receptor; SC, secretory component; SIg, secretory Ig; SpsA, S. pneumoniae SIgA-binding protein; MDCK, Madin-Darby canine kidney; PBS, phosphate-buffered saline; BSA, bovine serum albumin; ELISA, enzyme-linked immunosorbent assay; mAb, monoclonal antibody; NIP, 5-iodo-4-hydroxy-3-nitrophenylacetyl; TU, transducing unit. (1Brandtzaeg P. Farstad I.N. Johansen F.E. Morton H.C. Norderhaug I.N. Yamanaka T. Immunol. Rev. 1999; 171: 45-87Crossref PubMed Scopus (244) Google Scholar, 2Norderhaug I.N. Johansen F.E. Schjerven H. Brandtzaeg P.