In IgA nephropathy, there is abnormally glycosylated IgA1. Anti-glycan antibodies form and lead to immune complexes deposited within the mesangium of the glomeruli. These complexes attach to fibronectin or type IV collagen in the extracellular matrix and activate mesangial cells to produce extracellular matrix, leading to mesangial hypercellularity, segmental glomerulosclerosis or adhesion, tubular atrophy, and interstitial fibrosis.

The IgA is deposited mainly within the mesangium, which then increases mesangial cellularity as shown at the arrow. Patients with IgA nephropathy usually present with hematuria (nephritic syndrome). Older adults may also have proteinuria, microscopic hematuria, and hypertension. Most cases are idiopathic. Some cases occur when there is defective clearance of IgA with liver disease. Some cases occur in patients with celiac disease.