Responses to free lipopolysaccharide and Escherichia coli by normal human intestinal macrophages, following their migration out of the lamina propria.

Intestinal macrophage responses to luminal bacteria and their constituents are important in mucosal inflammatory responses. We investigated the responses of intestinal macrophages to free lipopolysaccharide (LPS) and Escherichia coli. Macrophages were isolated from normal terminal ileum and colon by allowing them to migrate out of the lamina propria of mucosal samples denuded of epithelial cells. Following exposure to free LPS or fluorescein-labelled E. coli, responsiveness was studied by intracellular expression of tumour necrosis factor-α (TNF-α). CD14, CD33, CD68, TLR2 and TLR4 expression was studied by fluorescence-activated cell sorter (FACS). TLR and NOD2 expression was confirmed by reverse-transcriptase polymerase chain reaction (RT-PCR). CD14 was expressed by 36.5 ± 4.0% of the macrophages obtained following migration out of the lamina propria. These cells also expressed TLR2, TLR4 and NOD2. Of cells exposed to free LPS or those that had taken up E. coli, a greater proportion of CD14+ than CD14– macrophages expressed intracellular TNF-α. Moreover, a greater proportion of macrophages (CD14+ and CD14–) demonstrated responses to E. coli than free LPS. In conclusion, a proportion of macrophages obtained following migration out of the lamina propria of normal terminal ileal and colonic mucosal samples express CD14, TLR2 and TLR4. These cells respond to free LPS and E. coli, as demonstrated by the expression of TNF-α.