Standardised assessment of membrane proteinase 3 expression. Analysis in ANCA-associated vasculitis and controls

Differential expression of granulopoiesis related genes in neutrophil subsets distinguished by membrane expression of CD177

Objective

Differential gene expression in CD177⁺ and CD177⁻ neutrophils was investigated, in order to detect possible differences in neutrophil function which could be related to the pathogenesis of ANCA-associated Vasculitides (AAV).

Methods

Neutrophils were isolated from healthy controls (HC) with high, negative or bimodal CD177 expression, and sorted into CD177⁺ and CD177⁻ subpopulations. Total RNA was screened for expression of 24,000 probes with Illumina Ref-8 Beadchips. Genes showing differential expression between CD177⁺ and CD177⁻ subsets in microarray analysis were re-assessed using quantitative-PCR. CD177 expression on neutrophil precursors in bone marrow was analyzed using quantitative PCR and flowcytometry.

Results

The proportion of CD177⁺ cells increased during neutrophil maturation in bone marrow. Fold change analysis of gene expression profile of sorted CD177⁺ and CD177⁻ neutrophils resulted in 14 genes with fold change (fc) >3 difference in expression. Interestingly, 10 of these genes have been reported to change significantly in expression during neutrophil maturation, and most of these genes were granule protein (GP) coding genes. mRNA expression levels measured by RT-PCR of a number of these GP, and of PR3 and MPO were higher in the CD177⁻ neutrophil subset in HC, however, particular granule protein amounts were comparable between CD177⁺ and CD177⁻ neutrophil subsets. AAV patients had higher amounts of CD177⁺ neutrophils, but contrary to neutrophils from HC expression of GP-genes was increased, possibly due to activation.

Conclusion

The neutrophil population can be distinguished by membrane expression of CD177 into subsets that are different in expression of GP mRNA but not in GP protein production. GP gene expression is also elevated in AAV patients, which is not explained by skewed distribution of CD177⁺ and CD177⁻ subsets but may be associated with neutrophil activation during on-going inflammation.

Antineutrophil cytoplasmic antibody-associated vasculitides: is it time to split up the group?

Antineutrophil cytoplasmic antibody (ANCA)-associated vasculitides are a heterogeneous group of diseases corresponding to necrotising inflammation of small vessels with a wide range of clinical presentations. At least two of the diseases are believed to exhibit a common ground of pathophysiological mechanisms. These are granulomatosis with polyangiitis (GPA, formerly known as Wegener's granulomatosis) and microscopic polyangiitis (MPA). ANCA directed against proteinase 3 (PR3) are preferentially associated with GPA, and anti-myeloperoxidase (MPO) ANCA are associated mainly with MPA and eosinophilic GPA (formerly known as Churg-Strauss syndrome). Anti-MPO and anti-PR3 antibodies can activate neutrophils in vitro. In vivo data are available for humans and mice on the pathogenicity of anti-MPO but it is more controversial for PR3-ANCA. A recent genome-wide association study of patients with ANCA-associated vasculitides confirmed the genetic contribution to the pathogenesis of these conditions, with significant association of PR3-ANCA and human leukocyte antigen-DP and the genes encoding α1-antitrypsin and PR3. MPO-ANCA were significantly associated with human leukocyte antigen-DQ. Thus, recent results from epidemiological studies, genome-wide association study and therapeutic trials have suggested that these entities are, in fact, distinct. We have summarised these results and discuss the idea that these two entities should be studied separately as the nature of the two auto-antigens suggests at a molecular level despite shared ANCA involvement.

ANCA-associated vasculitides--advances in pathogenesis and treatment

Antineutrophil cytoplasmic antibody (ANCA)-associated vasculitides (AAV) include Wegener granulomatosis, microscopic polyangiitis, Churg-Strauss syndrome and renal-limited vasculitis. This Review highlights the progress that has been made in our understanding of AAV pathogenesis and discusses new developments in the treatment of these diseases. Evidence from clinical studies, and both in vitro and in vivo experiments, supports a pathogenic role for ANCAs in the development of AAV; evidence is stronger for myeloperoxidase-ANCAs than for proteinase-3-ANCAs. Neutrophils, complement and effector T cells are also involved in AAV pathogenesis. With respect to treatment of AAV, glucocorticoids, cyclophosphamide and other conventional therapies are commonly used to induce remission in generalized disease. Pulse intravenous cyclophosphamide is equivalent in efficacy to oral cyclophosphamide but seems to be associated with less adverse effects. Nevertheless, alternatives to cyclophosphamide therapy have been investigated, such as the use of methotrexate as a less-toxic alternative to cyclophosphamide to induce remission in non-organ-threatening or non-life-threatening AAV. Furthermore, rituximab is equally as effective as cyclophosphamide for induction of remission in AAV and might become the standard of therapy in the near future. Controlled trials in which specific immune effector cells and molecules are being therapeutically targeted have been initiated or are currently being planned.

Membrane-bound proteinase 3 and its receptors: relevance for the pathogenesis of Wegener's Granulomatosis

Wegener's Granulomatosis (WG) is a life-threatening autoimmune disease. A pathogenic role for anti-neutrophil cytoplasmic autoantibodies (ANCAs) by inducing necrotizing damage to the vessel wall has been strongly suggested by in vitro and in vivo experimental data. Proteinase 3 (PR3), a serine protease mainly stored in the azurophilic granules of neutrophils, has been identified as a major ANCA-antigen in WG. Elevated expression levels of membrane-bound PR3 (mPR3) has been observed in WG and some other chronic inflammatory diseases, suggesting a pathogenic role of mPR3 by allowing interaction with PR3-ANCA. Recent studies revealed CD177 as a receptor for mPR3 on the neutrophil membrane. However, we recently showed that CD177 negative neutrophils also express mPR3 and are susceptible to PR3-ANCA induced neutrophil activation. Therefore, it is of interest to further investigate the functional consequences of binding of mPR3 to CD177, to explore other binding partners for mPR3 on the neutrophil membrane, and to study the relevance of colocalization of these molecules for disease pathogenesis. This review gives updated information on the mechanism of mPR3 expression and the relevance of colocalization of mPR3 with other molecules on the neutrophil membrane for the pathophysiological events occurring in WG.