Mac-1 (CD11b/CD18) is the predominant beta 2 (CD18) integrin mediating human neutrophil migration through synovial and dermal fibroblast barriers.

Recently we reported that polymorphonuclear leucocyte (PMNL) migration in vitro through a barrier of human synovial fibroblasts (HSF) involves both beta 2 (CD18) and beta 1 (CD29) integrins on the PMNL. Here we investigated the role of the beta 2 integrin family members, lymphocyte function-associated (LFA)-1 (alpha L beta 2 or CD11a/CD18) and Mac-1 ( alpha M beta 2 or CD11b/CD18), in PMNL migration through HSF and human dermal fibroblast (HDF) monolayers. Treatment of PMNL with monoclonal antibody (mAb) to LFA-1 (anti-alpha L) did not inhibit PMNL migration through either monolayer in response to C5a. In contrast, mAb to Mac-1 (Cd11b) inhibited (by 30-40%) PMNL migration, and by virtually the same extent as mAb to the beta 1 integrin chain (CD18) (40% inhibition). Addition of mAb to LFA-1 to mAb to Mac-1 did not result in greater inhibition. This was in contrast to PMNL migration through human umbilical vein endothelium (HUVE) monolayers, where mAb to LFA-1 or to Mac-1 each partially inhibited PMNL transendothelial migration, and when these mAbs were combined, synergistic inhibition of migration was observed, reaching 90-95% inhibition. Intercellular adhesion molecule 1 (ICAM-1) was not required for Mac-1 mediated migration through HSF or HDF, because treatment of the fibroblasts with mAb R6.5 (F(ab)2) to ICAM-1, which blocks the Mac-1 binding site on ICAM-1, did not inhibit PMNL migration. An LFA-1-ICAM-1 mechanism of PMNL migration through HSF and HDF monolayers could be detected after treatment (4 hr) of the monolayers with TNF-alpha plus IFN-gamma, which upregulated ICAM-1 on the fibroblasts. The results demonstrate the beta 2 integrin dependent PMNL migration in connective tissue may involve primarily Mac-1, with little involvement of LFA-1 or ICAM-1, a situation in marked contrast to PMNL migration across endothelium. However, in inflammatory conditions in which TNF-alpha and/or IFN-gamma may be generated, a role for LFA-1-ICAM-1 may be induced.