This is IgA nephropathy (Berger disease). 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). 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.