TNF and microscopic polyangiitis: In GPA and MPA, PR3-ANCA or MPO-ANCA-mediated neutrophil activation causes aortitis by releasing cytokines (e.g., tumor necrosis factor (TNF)-alpha and IL-1) and matrix metalloproteinases (MMPs) that degrade elastin and collagen in the aortic media, weakening the vessel wall [5,7,8].