Histologic Evaluation
The biopsy specimens were processed for light microscopy, immunofluorescence and electron microscopy. Paraffin sections for light microscopy were stained with hematoxylin and eosin, periodic acid-Schiff, and Masson’s trichrome stain for pathologic analysis. Direct immunofluorescence for IgA, IgG, IgM, and C3 was performed in frozen sections. Clinical renal pathologists performed qualitative assessment of the degree of immunofluorescent staining. The degree of glomerular C3 immunofluorescent stain intensity was reported on a scale of 1+ to 3+, with 1+ representing low-intensity staining; 2+, medium-intensity staining; or 3+, high-intensity staining. Glomerular IgG and IgM deposition were graded by absent (score, 0), mild (score, 1), marked (score, 2), respectively. Glomerular IgA deposition were graded by IgA=2+ and IgA>2+. Pathological features were scored using the existing literature [14, 15]. In particular, mesangial hypercellularity, segmental glomerulosclerosis, endocapillary hypercellularity, tubular atrophy/interstitial fibrosis were graded by Oxford classification. For each biopsy, we determined the fraction of glomeruli with cellular or fibrocellular or fibrous crescents. A crescent was defined as extracapillary proliferation of more than two cell layers of any size; this definition was uniform in all studies. The severity of global glomerulosclerosis and arterial wall thickening was graded in three groups: absent (score, 0), mild (score, 0), and marked (score, 0). Crescents and arterial hyalinosis were scored as either absent or present.