Alveolar hemorrhage and renal microangiopathy in systemic lupus erythematosus.

CONTEXT: Acute alveolar hemorrhage in systemic lupus erythematosus usually occurs as a pulmonary-renal syndrome. In most cases, the lungs show "bland" alveolar hemorrhage with little or no inflammation. Whether this alveolar injury is similar to the better-defined noninflammatory renal lupus vasculopathy is unresolved.
OBJECTIVES: To investigate the relationships and the mechanisms of small vascular injury in the lung and kidney of 2 lupus patients who died of diffuse AH.
METHODS: We investigated the relationship of AH to immune complex deposition in the lungs of 6 patients with systemic lupus erythematosus and correlated the findings with glomerular and vascular disease in the kidney. Lung and kidney were studied by light, immunofluorescence, and/or electron microscopy; apoptosis was investigated using in situ nick-end labeling.
RESULTS: The clinical course of 2 patients was complicated by alveolar hemorrhage, and the lungs of these patients revealed alveolar wall immune complex deposits and bland alveolar hemorrhage. These 2 patients had World Health Organization class IV lupus nephritis and renal arterioles involved by a noninflammatory lupus vasculopathy. Apoptosis was identified in the lupus microangiopathy and in alveolar walls within areas of alveolar hemorrhage. Alveolar wall immune complex deposits were not found in 4 patients who had a lupus glomerulonephritis but did not have renal lupus vasculopathy. Apoptosis was not seen in renal arterioles or lungs of these 4 cases, except in areas of diffuse alveolar damage or herpesvirus pneumonia.
CONCLUSIONS: Our findings indicate that alveolar hemorrhage in systemic lupus erythematosus, characterized by bland alveolar wall changes, is pathogenetically similar to the lupus microangiopathy of the kidney. In both lung and kidney, the pathogenesis of the microvascular injury appears to be related to immune complex deposition and the induction of apoptosis.