ANCA antigens, proteinase 3 and myeloperoxidase, are not expressed in endothelial cells

Background. One hypothesis for the pathogenesis of vasculitis associated wi th antineutrophil cytoplasmic autoantibodies (ANCAs) proposes that ANCAs bi nd to ANCA antigens, such as proteinase 3 (PR3) or myeloperoxidase (MPO), w hich are produced by endothelial cells and expressed on their surfaces. The re are conflicting reports, however, on whether endothelial cells express t he ANCA antigen PR3, and there are no reports on endothelial expression of MPO. The aim of this study was to determine the presence or absence of PR3 and MPO mRNA in both venous and arterial endothelial cells, employing stand ard reverse transcription-polymerase chain reaction (RT-PCR) techniques and also the quantitative and highly specific method, TaqMan PCR. Methods. RT-PCR (with 3 primer sets) and TaqMan PCR, a method for detecting low copy transcripts, were used to probe for PR3 and MPO transcripts in hu man endothelial cells from umbilical vein (HUVEC) and artery (HUAEC) and fr om lung microvascular (HLMVEC). Cells were treated with interferon-gamma (2 00 units/mL) or tumor necrosis factor-alpha (3 or 10 ng/mL) or both. Results. Transcripts for PR3 and/or MPO were not detected in HUVEC, HUAEC, and HLMVEC by standard RT-PCR. Analyses for PR3 protein confirmed that PR3 is not expressed in HUVEC. HUVEC and HUAEC were negative for PR3 and MPO by TaqMan PCR. Conclusions. PR3 and MPO are not expressed in HUVEC, HUAEC, or HLMVEC. Endo thelial cell presentation of endogenous PR3 and MPO antigens is not involve d in the pathogenesis of ANCA-associated vasculitis. Alternative explanatio ns need to be explored to determine the pathogenic effect of ANCAs.