Pathophysiology
Clinical meaning
Pulmonary vasculitis involves inflammation and destruction of blood vessel walls in the lungs, mediated by autoantibodies (ANCA), immune complexes, or T-cell-mediated mechanisms. In granulomatosis with polyangiitis (GPA), anti-PR3 antibodies (c-ANCA) activate neutrophils that infiltrate vessel walls, causing necrotizing granulomatous inflammation. In microscopic polyangiitis (MPA), anti-MPO antibodies (p-ANCA) cause pauci-immune capillaritis. The damaged vessels allow blood and inflammatory exudate to leak into alveoli, causing diffuse alveolar hemorrhage, while granuloma formation can cavitate and destroy lung parenchyma.