It has been shown previously that certain bacteria rapidly (3 h) up-regulated in vivo microfold cell (M cell)-mediated transport
of Ag across the follicle-associated epithelium of intestinal Peyer’s patch. Our aim was to determine whether soluble mediators
secreted following host-bacteria interaction were involved in this event. A combination of proteomics and immunohistochemical
analyses was used to identify molecules produced in the gut in response to bacterial challenge in vivo; their effects were then tested on human intestinal epithelial cells in vitro. Macrophage migration inhibitory factor (MIF) was the only cytokine produced rapidly after in vivo bacterial challenge by CD11c cells located beneath the M cell-rich area of the follicle-associated epithelium of the
Peyer’s patch. Subsequently, in vitro experiments conducted using human Caco-2 cells showed that, within hours, MIF induced
the appearance of cells that showed temperature-dependent transport of microparticles and M cell-specific bacterium Vibrio
cholerae, and acquired biochemical features ofMcells. Furthermore, using an established in vitro humanMcell model, we showed that anti-MIF Ab blocked Raji B cell-mediated conversion of Caco-2 cells into Ag-sampling cells. Finally, we report that MIF/
mice, in contrast to wild-type mice, failed to show increased M cell-mediated transport following in vivo bacterial challenge. These
data show that MIF plays a role inMcell-mediated transport, and cross-talk between bacteria, gut epithelium, and immune system
is instrumental in regulating key functions of the gut, including M cell-mediated Ag sampling
