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Immunol."],"abstract":"<jats:p>In mucosa such as tonsil, antibody-producing plasmocytes (PCs) lie in sub-epithelium space, which is thought to provide a suitable environment for their survival. A proliferation inducing ligand (APRIL) is one key survival factor for PCs present in this area. According to <jats:italic>in situ<\/jats:italic> staining, apical epithelial cells produced APRIL, and the secreted product had to migrate all through the stratified surface epithelium to reach basal cells. A similar process also occurred in the less-organized crypt epithelium. Tonsil epithelial cells captured secreted APRIL, thanks to their surface expression of the APRIL coreceptor, either syndecan-1 or -4 depending on their differentiation stage. In the most basal epithelial cells, secreted APRIL accumulated inside secretory lamp-1<jats:sup>+<\/jats:sup> vesicles in a polarized manner, facing the sub-epithelium. The tonsil epithelium upregulated APRIL production by apical cells and secretion by basal cells upon Toll-like receptor stimulation. Furthermore, LPS-stimulated epithelial cells sustained <jats:italic>in vitro<\/jats:italic> PC survival in a secreted APRIL-dependent manner. Taken together, our study shows that the tonsil epithelium responds to pathogen sensing by a polarized secretion of APRIL in the sub-epithelial space, wherein PCs reside.<\/jats:p>","DOI":"10.3389\/fimmu.2021.715724","type":"journal-article","created":{"date-parts":[[2021,8,18]],"date-time":"2021-08-18T08:04:00Z","timestamp":1629273840000},"update-policy":"https:\/\/doi.org\/10.3389\/crossmark-policy","source":"Crossref","is-referenced-by-count":2,"title":["Polarized Secretion of APRIL by the Tonsil Epithelium Upon Toll-Like Receptor 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