Increased Escherichia coli phagocytosis in neutrophils that have transmigrated across a cultured intestinal epithelium.

The functionality of polymorphonuclear leukocytes (PMNs) once they migrate into the digestive lumen is still ill defined. More specifically, phagocytic function and bactericidal action of PMNs after transepithelial migration have not received much attention. The aim of the present study is to compare PMN behavior before and after transepithelial migration, in particular (i) phagocytosis and bactericidal activity; (ii) expression of surface molecules, particularly those involved in phagocytosis; and (iii) apoptosis. Cultured human intestinal epithelial T84 cell monolayers were used. The effect of transepithelial migration on phagocytosis was evaluated by immunofluorescence and electron microscopy and by flow cytometric assessment of the engulfment of a strain of Escherichia coli transfected with the green fluorescent protein. Superoxide production by PMNs was investigated by luminol-mediated chemiluminescence. Expression of various surface molecules on PMNs was evaluated by flow cytometry, while PMN apoptosis was assayed by morphologic changes and DNA fragmentation. E. coli phagocytosis by the PMNs was markedly increased after transepithelial migration without modification of superoxide production. CD11b/CD18 and CD47 expression was increased upon PMN transmigration, whereas CD16 expression was decreased and CD29, CD46, CD49e, CD49f, CD55, CD59, CD61, CD95 levels remained unchanged. Apoptosis in transmigrated PMNs was slightly advanced and was observed after 12 h compared to 16 h for nontransmigrated PMNs. In conclusion, the phagocytic capacity of the PMNs is augmented after transepithelial migration, with a dramatic increase in the level of CD11b/CD18 and preservation of the superoxide production. These results suggest a higher bactericidal activity of the PMNs once they have translocated into the digestive lumen.