We investigated membrane
proteinase 3 (mPR3) expression during
TNF-alpha-induced adhesion of neutrophils in the presence of anti-PR3
antibodies, a situation occurring during
anti-neutrophil cytoplasmic autoantibodies (
ANCA)-associated vasculitis. Three increasing levels of mPR3 expression were observed on the mPR3(+) neutrophil subset after stepwise cell activation.
TNF-alpha activation without adhesion,
TNF-alpha-induced adhesion, and adhesion in the presence of anti-PR3 mAb or human anti-PR3
ANCA resulted, respectively, in a two-, seven-, and 24-fold increase of mPR3 levels. In plasma, anti-PR3
antibodies poorly recognized suspended neutrophils, whereas they bound to mPR3 on adherent cells. mPR3 upregulation was also triggered by
IL-8, formyl-
methionyl-leucyl-phenylalanine (fMLP), and neutrophil adhesion to activated human umbilical vein endothelial cells. It involved beta2
integrins and Fcgamma receptor, because it was prevented by anti-CD18
antibodies and was not observed with anti-PR3 F(ab')(2). Furthermore, it was specific to anti-PR3 mAb, and no mPR3 upregulation was observed with anti-
myeloperoxidase or anti-HLA-ABC mAb. Newly expressed mPR3 molecules, after TNF-induced adhesion, were mobilized from secretory vesicles (CD35(+)) and secondary granules (CD11b(+)). The adhesion- and antibody-dependent upregulations of mPR3 expression occurred with little azurophilic granule degranulation, no sign of apoptosis, and no further CD177 upregulation. In conclusion, this study describes an amplifying loop in polymorphonuclear neutrophil activation process, whereby
ANCA are involved in the membrane expression of their own
antigen during cell adhesion. This could explain the restriction of
ANCA-associated vasculitis to small vessels, the main site of neutrophil adhesion.