Migration of human polymorphonuclear leukocytes through a synovial fibroblast barrier is mediated by both β₂ (CD11/CD18) integrins and the β₁ (CD29) integrins VLA-5 and VLA-6

Polymorphonuclear leukocytes (PMNL) accumulate in joint fluid in inflammatory arthritides. We investigated the molecular mechanisms required for PMNL migration through a barrier of human synovial fibroblasts (HSF) grown on microporous filters, as a model of PMNL migration through synovial connective tissue and compared this process with PMNL migration through human dermal fibroblast (HDF) barriers and through human umbilical vein endothelium (HUVE). A small amount of PMNL migration occurred spontaneously only through the synovial fibroblast/filter unit (6-10%). Migration markedly increased through all cell monolayers when the chemotactic factors C5a, IL-8, or zymosan-activated plasma (containing C5a_desArg) were added to form a chemotactic gradient. The migration induced by C5a, IL-8, or C5a_desArg across HSF was partially inhibited (25-76% depending on stimulus) by mAb to CD18 (β₂integrin). The CD18-independent migration induced by IL-8 or C5a_desArg was almost completely inhibited by mAbs to β₁ integrin, but with C5a, inhibition by mAb to β₁ integrin was only partial (40-50%). Inhibition by mAb to β₁ integrin required treatment of the PMNL, but not the HSF and was only observed when the function of CD11/CD18 on PMNL was also blocked by a mAb. Treatment of PMNL with mAb to α₅ (VLA-5) plus α₆ (VLA-6) in combination, was required to inhibit CD18-independent migration through HSF to the degree observed with mAb to β₁ integrin. There was no qualitative difference in the mechanisms utilized by PMNL for migration through HSF or HDF in response to chemotactic factors. In contrast, PMNL migration across HUVE was almost completely CD18-dependent (85%) with no role for β₁ integrins. The results suggest that (a) PMNL migration through HSF in response to chemotactic factors utilizes both CD11/CD18 and β₁ (CD29) integrins; (b) the VLA-5 and VLA-6 members of β₁ integrins are involved in mediating migration; and (c) PMNL utilize similar mechanisms for migration through HSF and HDF, which are distinct from migration through HUVE.