Neutrophils migrate across intestinal epithelium using β 2 integrin (CD11b/CD18)‐independent mechanisms

SUMMARY Recruitment of polymorphonuclear leucocytes (PMN) across the intestinal epithelium is dependent on specific adhesion molecules and chemoattractants diffusing from the intestinal lumen. The present understanding is that in response to fMLP, PMN migration across a T84 colon carcinoma monolayer is dependent on the β 2 integrin, Mac‐1 (CD11b/CD18). To further understand PMN transepithelial migration, we sought to determine whether migration to C5a, IL‐8 and LTB 4 was similarly Mac‐1‐, or even CD18‐dependent. T84 epithelial cell monolayers growing on Transwell filters were used in combination with radiolabelled peripheral blood PMN. The number of migrated PMN was established by the amount of radioactivity recovered from the well after the migration period. Monoclonal antibodies were used to block integrin function. Whereas essentially all migration to fMLP across T84 monolayers was prevented by anti‐CD18 antibody, significant migration to C5a, IL‐8 or LTB 4 persisted despite anti‐CD18 antibody, indicating PMN are capable of β 2 integrin‐independent transepithelial migration. An antibody to  CD11b  but  not  CD11a  blocked  migration  to  an  extent  similar  as  with anti‐CD18.  CD18‐independent  PMN migration to C5a occurred only in the basolateral‐to‐apical direction across epithelial cells.  Co‐stimulation of PMN with C5a and fMLP or IL‐8 plus LTB 4 and fMLP still resulted in CD18‐independent migration. Thus CD18 use during PMN migration across this model epithelium is a function of the chemoattractant inducing migration. The finding of CD18‐independent migration mechanisms needs to be considered when developing antiadhesion molecule strategies to reduce or reverse intestinal inflammation.