Acute nephritis and pulmonary alveolitis following pneumococcal pneumonia.

Acute glomerulonephritis developed in a man with pneumococcal pneumonia. Serum complement studies revealed decreased levels of C4, properdin, and C3. Renal immunofluorescence studies demonstrated pneumococcal antigen, C1q, C4, C3 proactivator, properdin, C3, IgG, and IgM. Circulating cryoglobulin contained pneumococcal antigen and antibody, C3, and immunoglobulins. Serial pneumococcal antigen and antibody levels did not display patterns that were characteristic of classical immune elimination, but the patterns may have been influenced by the reentry of antigen. A diffuse, pulmonary alveolitis also developed in the patient. Lung immunofluorescence studies revealed pneumococcal antigen, IgG, and C3 in alveolar walls and capillary basement membranes. The glomerulonephritis and alveolitis resolved after a prolonged course. These findings provide presumptive evidence for pneumococcal, immune complex glomerulonephritis with complement activation via both classical and alternative pathways and suggest an immunologic pathogenesis for the pulmonary alveolitis.