C3 and IgA glomerulonephritis: Primary IgA nephropathy is characterized by elevation of serum IgA, the absence of systemic features, and the following renal biopsy findings: LM shows mesangial hypercellularity and an increase of matrix, IF demonstrates IgA staining (often accompanied by C3) in the mesangium and lesser staining along the glomerular capillary walls, and EM typically reveals electron-dense deposits that are primarily limited to the mesangium.