Transepithelial Secretion of Mucosal IgM Mediated by Polymeric Immunoglobulin Receptor of Flounder (Paralichthys olivaceus): In-Vivo and In-Vitro Evidence

• DOI: 10.3389/fimmu.2022.868753
• Publication Date: 2022-04-06T06:47:38Z
• Authors: Xiuzhen Sheng; Yuan Guo; Hui Zhu; Baihui Chai; Xiaoqian Tang; Jing Xing; Heng Chi; Wenbin Zhan
• Keywords: Polymeric immunoglobulin receptor; Lamina propria; J chain; Immunoglobulin M; Secretory component; Immunoglobulin A

Secretory immunoglobulin (SIg) is crucial for mucosal surface defenses, but the transepithelial secretion of SIg mediated by polymeric receptor (pIgR) not clarified in fish. We previously found that flounder ( Paralichthys olivaceus ) pIgR (fpIgR) and secretory IgM (SIgM) increased gut mucus post-vaccination. Here, fpIgR-positive signal was mainly observed intestinal epithelium, whereas IgM-positive distributed lamina propria, before immunization. signals propria then epithelium after immunization with inactivated Vibrio anguillarum , co-localization between fpIgR determined, while presence EdU + cells identified proliferative B cells, revealing transport SIgM locally occurred flounder. Subsequently, we established an in-vitro model transfected MDCK stably expressed fpIgR. After a recombinant eukaryotic expression plasmid (pCIneoEGFP-fpIgR) constructed into stable MDCK-fpIgR confirmed, tightness integrity polarized cell monolayers grown on Transwells were evaluated. Afterward, serum purified as binding ligand placed lower compartment Transwells. An ~800-kDa protein band upper shown to be IgM- fpIgR-positive, fluorescence seen MDCK-mock cells. Hence, helped pass across via transcytosis basolateral-to-apical fashion. These new findings provide better understanding pathways shaping responses local immune mechanisms teleosts.