CD28 and granulomatosis with polyangiitis: Granulomata consist of neutrophils, giant cells, monocyte-derived tissue macrophages, B cells and CD4+CD28− T cells.18 The activation of T cells in an unbalanced Th1 phenotype and maturation of dendritic cells by PR3, exaggerating this Th1 response, have previously highlighted Th1 cells as critical mediators of granuloma pathogenesis in GPA.18,19 Indeed, both CD4+ Th1 and Th17 cells have been implicated as important orchestrators of granulomatous inflammation.