Figure 4

MGC forms in the presence of enzymatically active and inactive PR3. No statistical difference in fusion index was seen in the cells from patients with GPA when stimulated with enzymatically active or heat-inactivated (Hi) PR3 (A). PAR-2 agonism increased the fusion index in patients with GPA, and PAR-2 antagonism significantly inhibited the rates of MGC formation (B). The presence of PR3-ANCA or MPO-ANCA alone had no effect on fusion index compared with control immunoglobulin (C); however, when cultured with PR3, there was a significant increase in MGC formation in the presence of PR3-ANCA and control immunoglobulin compared with MPO-ANCA. Patients with GPA with different ANCA subtypes (D). Patients with PR3-ANCA GPA showed a significant increase in monocyte fusion compared with healthy controls and patients with MPO-ANCA MPA; however, a similar increase in MGC formation was seen in patients with MPO-ANCA GPA. Values plotted as median and 95% CI; *p<0.05, **p<0.01, ***p<0.001, ****p<0.0001. Difference between conditions determined by one-way and two-way ANOVA tests. ANCA, antineutrophil cytoplasm antibodies; ANOVA, analysis of variance; GPA, granulomatosis with polyangiitis; MGC, multinucleated giant cells; MPA, microscopic polyangiitis; MPO, myeloperoxidase; PAR-2, protease-activated receptor-2; PR3, proteinase 3; unstim, unstimulated.