Inhibition of neutrophil-mediated production of reactive oxygen species (ROS) by endothelial cells is not impaired in anti-neutrophil cytoplasmic autoantibodies (ANCA)-associated vasculitis patients

Leucocyte transendothelial migration is strictly regulated to prevent undesired inflammation and collateral damage of endothelial cells by activated neutrophils/monocytes. We hypothesized that in anti‐neutrophil cytoplasmic autoantibodies (ANCA)‐associated vasculitis (AAV) patients' dysregulation of this process might underlie vascular inflammation. Peripheral blood mononuclear cells (PBMC) and neutrophils from AAV patients (n = 12) and healthy controls (HC, n = 12) were isolated. The influence of human umbilical vein endothelial cells (HUVEC) on neutrophil/monocytes function was tested by N‐formyl‐methionyl‐leucyl‐phenyl‐alanine (fMLP)‐ and phorbol 12‐myristate 13‐acetate (PMA)‐mediated ROS production, degranulation and interleukin (IL)‐8 production. In addition, the ability of lipopolysaccharide (LPS)‐stimulated PBMC to produce tumour necrosis factor (TNF)‐α in the presence or absence of HUVEC was tested. HUVEC inhibited ROS production dose‐dependently by fMLP‐stimulated neutrophils but did not influence degranulation. No differences between neutrophils from HC and AAV were found. However, in only one active patient was degranulation inhibited significantly by HUVEC only before cyclophosphamide treatment, but not 6 weeks later. Co‐cultures of HUVEC with LPS‐stimulated neutrophils/monocytes increased IL‐8 production while TNF‐α production was inhibited significantly. There was no apparent difference between AAV patients and HC in this respect. Our findings demonstrate that HUVEC are able to inhibit ROS and modulate cytokine production upon stimulation of neutrophils or monocytes. Our data do not support the hypothesis that endothelial cells inhibit ROS production of neutrophils from AAV patients inadequately. Impaired neutrophil degranulation may exist in active patients, but this finding needs to be confirmed.