Involvement of Fcγ receptors and β2 integrins in neutrophil activation by anti‐proteinase‐3 or anti‐myeloperoxidase antibodies
We previously described the requirement of tumour necrosis factor‐alpha (TNF‐α) and the role of β2 integrins in the Fc‐gamma receptor IIa (FcγRIIa)‐mediated mechanism of neutrophil activation by antiproteinase‐3 (anti‐PR3) or anti‐myeloperoxidase (anti‐MPO) antibodies. In the present study, we assessed  the  involvement  of  FcγRIIIb  by  studying  the  respiratory  burst  activation  of  completely FcγRIIIb‐deficient  neutrophils  primed  by  TNF‐α and  exposed  to  anti‐PR3  or  anti‐MPO.  Activation of the NADPH oxidase occurred normally in these neutrophils, which indicates that engagement of FcγRIIIb is not essential in our model. Experiments performed with neutrophils from severe leucocyte adhesion deficiency (LAD) patients confirmed that β2 integrins play a pivotal role in this activation. We next studied whether adhesion per se, β2‐integrin‐mediated adhesion, or β2‐integrin ligation without adhesion is necessary or sufficient for this activation. Anti‐PR3 or anti‐MPO induced an FcγRIIa‐dependent burst in TNF‐primed neutrophils incubated in wells coated with poly‐l‐lysine, known to induce β2‐integrin‐independent adhesion, but this reaction was still inhibited by blocking CD18 antibodies. In a system with granulocyte‐macrophage colony‐stimulating factor (GM‐CSF)‐primed neutrophils, which did not enhance adhesion, we measured a similar activation by anti‐PR3 or anti‐MPO and inhibition by CD18. We also noticed that treatment with the β2‐integrin‐activating CD18 MoAb KIM185 per se is insufficient for neutrophil activation by anti‐PR3 or anti‐MPO. We therefore conclude that ligation of β2 integrins rather than adherence per se is essential for this activation, and that TNF‐α or GM‐CSF is needed for priming but not for adherence.