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, phagocyti c function and bactericidal action of PMNs after transepithelial migration have not received much attention. The aim of the present study is to compar e PMN behavior before and after transepithelial migration, in particular (i ) phagocytosis and bactericidal activity; (ii) expression of surface molecu les, particularly those involved in phagocytosis; and (iii) apoptosis, Cult ured human intestinal epithelial T84 cell monolayers were used, The effect of transepithelial migration on phagocytosis was evaluated by immunofluores cence and electron microscopy and by flow cytometric assessment of the engu lfment of a strain of Escherichia coli transfected with the green fluoresce nt protein. Superoxide production by PMNs was investigated by luminol-media ted 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 marked ly increased after transepithelial migration without modification of supero xide production, CD11b/CD18 and CD47 expression was increased upon PMN tran smigration, whereas CD16 expression was decreased and CD29, CD46, CD49e, CD 49f, CD55, CD59, CD61, CD95 Levels remained unchanged. Apoptosis in transmi grated PMNs was slightly advanced and was observed after 12 h compared to 1 6 h for nontransmigrated PMNs, In conclusion, the phagocytic capacity of th e PMNs is augmented after transepithelial migration, with a dramatic increa se in the level of CD11b/CD18 and preservation of the superoxide production . These results suggest a higher bactericidal activity of the PMNs once the y have translocated into the digestive lumen.