Increased production of the ether-lipid platelet-activating factor in intestinal epithelial cells infected by Salmonella enteritidis

When exposed to enteric pathogens intestinal epithelial cells produce several cytokines and other proinflammatory mediators. To date there is no evidence that the ether-lipid platelet-activating factor (PAF) is one of these mediators. Our results revealed a significant increase in PAF production by human colonic tissue 4 h after infection by enterohemorrhagic Escherichia coli (EHEC) or Salmonella enteritidis. PAF is produced in the gut by cells of the immune system in response to bacterial infection. To determine whether the epithelial cells of colonic mucosa might also modulate PAF levels, we carried out PAF quantification and analysis of the enzymes involved in PAF synthesis in 5-day-old (undifferentiated) or 28-day-old (differentiated) Caco-2 cell cultures. Infection of undifferentiated Caco-2 cells with either bacterium had no effect on PAF levels, whereas in differentiated cells, infection by S. enteritidis increased PAF levels.Following infection by S. enteritidis, there were no changes in the activity of dithiothreitol-insensitive choline phosphotransferase. However, the enzymes of the remodeling pathway cytosolic phospholipase A2, which catalyzes the formation of the PAF precursor lysoPAF, and lysoPAF acetyltransferase, are activated in the infected epithelial cells. This response is Ca2+-dependent.