Superimposition of post-streptococcal acute glomerulonephritis on the course of IgA nephropathy: Predominance of Th1 type immune response

A 23-year-old man was admitted with macrohematuria and systemic edema appearing after an acute upper respiratory tract infection. He had been diagnosed 6 years earlier with IgA nephropathy (IgA-N). On admission, hypertension, nephrotic syndrome and hypocomplementemia were evident together with a high titer of anti-streptokinase (ASK). Renal biopsy showed severe glomerular mesangial proliferation, segmental endo-capillary proliferation and crescent formation. Immunofluorescence microscopy (IF) showed strong deposition of C3 and reduced deposition of IgA. Electron microscopy showed a so-called "hump" on the epithelial side of the glomerular basement membrane. These features were consistent with post-streptococcal acute glomerulonephritis (PSAGN) superimposed on IgA-N. Following 2 weeks of observation, blood pressure, C3 level and ASK titer returned to normal ranges, although nephrotic syndrome was still evident, which necessitated oral prednisolone (30 mg/day) therapy. Another biopsy taken 2 months later demonstrated regression of endocapillary proliferation and IF showed decreased deposition of C3. Immunohistochemical staining of the specimen taken on admission revealed the presence of numerous T cells and macrophages in the interstitium. Macrophages were also seen in the glomerular tuft. Many interstitial infiltrating cells were positive for interferon-γ, but their number diminished after treatment. Our findings suggest that PSAGN complicating pre-existing IgA-N activates cellular immunity and augments renal tissue injury.