Up-regulation of microsphere transport across the follicle-associated epithelium of Peyer's patch by exposure to Streptococcus pneumoniae R36a

Transport of antigens through the follicle-associated epithelium (FAE) of P eyer's patch (PP) is the critical first step in the induction of mucosal im mune responses. We have previously described that short-term exposure to St reptococcus pneumoniae R36a induced dramatic morphological alterations of t he FAE in rabbit PP. These results prompted us to investigate whether the p neumococci-induced modifications were accompanied by enhanced ability of th e FAE to transport antigens. We addressed this problem by evaluating the ab ility of the FAE to bind, internalize, and transport fluorescent polystyren e microparticles, highly specific to rabbit M cells, after exposure to S. p neumoniae. Quantitative study revealed a marked increase in the number of m icrospheres in PP tissues exposed to S. pneumoniae compared to tissues expo sed to either phosphate-buffered saline or Escherichia coli DH5 alpha as co ntrols. No sign of bacterially induced damage to the epithelial barrier was observed. Further confocal microscopy analysis of the FAE surface showed t hat a significant increase in the number of cells that showed both morpholo gical and functional features of M cells took place within pneumococci-trea ted PP tissues. These data provide the first direct evidence that the FAE-s pecific antigen sampling function may be manipulated to improve antigen and drug delivery to the intestinal immune system.