Immunofluorescence staining of IgA1 deposits in ARPC-derived spheroids from IgAN patients and healthy subjects. ARPC-derived IgAN spheroids exhibited IgA1 deposits 4 days (A), 8 days (B), and 15 days (C) after the addition of IgAN patient serum. (D) IgA1 deposition in the glomerulus of a patient diagnosed with IgAN. (E) IgA1 immunostaining of IgAN spheroids cultured with FBS for 15 days. (F) IgA1 immunostaining of IgAN spheroids cultured without FBS for 15 days. (G) IgA1 immunostaining of ARPC-derived spheroids from healthy controls cultured with IgAN patient serum for 15 days. (H) IgA1 immunostaining of ARPC-derived spheroids from healthy controls cultured with inactivated IgAN patient serum for 15 days. (I) Fluorescence levels of IgA1 deposits in IgAN spheroids cultured with IgAN patient serum for 4 days (1), 8 days (2), or 15 days (3); in IgAN patient glomeruli (4); in IgAN spheroids cultured with FBS (5) or without FBS (6); in healthy subjects with inactivated IgAN patient serum (7); or in those cultured with IgAN patient serum (8). The scale bars represent 50 μm in A-C and 25 μm in E-H. Results are representative of 3 independent experiments (3 different IgAN patients). The immunofluorescent quantification from triplicate samples is shown in the histogram as mean ± SEM. **P <.01; ***P <.001.