Prostaglandin E2 (PGE2 ) plays a critical role in intestinal mucosal tolerance and barrier integrity. Cyclooxygenase-2 (COX-2)-dependent PGE2 production involves mobilization of arachidonic acid (AA). Lactobacillus rhamnosus GG (LbGG) is one of the most widely used probiotics reported to colonize the colonic mucosa. LbGG contributes to the protection of the small intestine against radiation injury through the repositioning of mucosal COX-2 expressing cells. However, it is unknown if LbGG modulates PGE2 production in the colonic mucosa under homeostasis and the major cellular elements involved in these processes. Colonic epithelial and CD90+ mesenchymal stromal cells, also known as (myo) fibroblasts (CMFs), are abundant innate immune cells in normal colonic mucosa able to produce PGE2 . Herein, we tested the hypothesis that under colonic mucosal homeostasis LbGG modulates the eicosanoid pathway resulting in increased PGE2 production in both epithelial and stromal cells. Among the five tested human colonic epithelial cell lines, only exposure of Caco-2 to LbGG for 24 h led to the mobilization of arachidonic acid (AA) with concomitant increase in the components within the leukotriene and COX-2 dependent PGE2 pathways. By contrast, CMFs isolated from the normal human colonic mucosa responded to LbGG with increased expression of COX-2 and PGE2 in the prostaglandin pathway, but not 5-LO in the leukotriene pathway. Oral gavage of C57BL/6 mice for 5 days with LbGG (5x108 CFU/dose) increased COX-2 expression in the colonic mucosa. The majority of cells upregulating COX-2 protein expression were located in the colonic lamina propria, and co-localized with alpha-SMA+ cells corresponding to the CMF phenotype. This process was MyD88 dependent, since silencing of MyD88 expression in CMFs abrogated LbGG-induced upregulation of COX-2 in culture and in vivo. Taken together, our data suggests that LbGG increases release of COX-2 mediated PGE2 , contributing to the maintenance of mucosal homeostasis in the colon and CMFs are among the major contributors to this process.< Leer menos