HUMAN NEUTROPHILS DO NOT DEGRADE MAJOR BASEMENT-MEMBRANE COMPONENTS DURING CHEMOTACTIC MIGRATION

At sites of inflammation, circulating neutrophils (PMNs) migrate throu gh microvessel walls into the subendothelial interstitium. While endot helial passage is mediated by adhesion proteins, including those of th e integrin, selectin and immunoglobulin superfamily classes, the mecha nisms used to cross the subendothelial basement membrane (BM) are uncl ear. Studies examining tumour cell invasion and lymphocyte extravasati on suggest several possible mechanisms, including proteolysis. Differe nt cells, however, may use different mechanisms to effect passage. To examine neutrophil-basement membrane interactions in more detail, huma n PMNs were embedded within reconstituted BM (Matrigel) and used in mi gration assays. The integrity of the gel following migration was asses sed by assaying for the release of incorporated radiolabelled products and by immunoblotting for specific matrix molecule epitopes. PMNs mig rated through]Matrigel in response to the chemotactic peptide FMLP. De gradation products of laminin, heparan sulphate proteoglycan or of gel atin, however, were not detected. In contrast, phorbol ester, which tr iggers activation,without migration, released similar to 40% of incorp orated HSPG, 30% of gelatin and 20% of laminin as intact molecules or degraded fragments. Electron microscopy of migrating cells demonstrate d pseudopodia associated with channels within the Matrigel. Although t he serine proteinase inhibitor DPP, plasma and a specific anti-neutrop hil elastase IgG blocked degradation, these agents failed to inhibit m igration. Migration was inhibited, however, when the Matrigel concentr ation was increased to 10 mg/ml. Thus, although PMNs will degrade matr ix components they do not do so during migration, and proteolytic remo delling of the BM is not a pre-requisite for neutrophil passage. Copyr ight (C) 1997 Elsevier Science Ltd.