Immunoglobulin A (IgA) nephropathy (IgAN) is characterized by high serum IgA levels and IgA deposition in the renal mesangium. Previous studies suggest that elevated serum IgA partly originates from the tonsils. Here, we investigated the mechanisms of IgA production in the tonsils of patients with IgAN. Immunohistochemistry revealed that the number and relative percentage of IgA-bearing cells were significantly increased in the tonsils of IgAN patients. Compared with non-IgAN patients, enhanced IgA class switching and overexpression of thymic stromal lymphopoietin (TSLP), TSLP receptor (TSLPR), activation-induced cytidine deaminase (AID), transforming growth factor-β1 (TGF-β1), B cell-activating factor of the tumor necrosis factor family (BAFF), and a proliferation-inducing ligand (APRIL) were detected in follicular dendritic cells (FDCs) of tonsillar germinal centers from IgAN patients. Importantly, TSLP correlated with IgA production in isolated FDC-associated clusters. Serum TSLP levels were increased and correlated with IgA overexpression in the tonsils and serum of IgAN patients. These data indicated that TSLP overexpression in tonsillar FDCs may promote IgA class switching in IgAN patients through the cooperative roles of AID, TGF-β1, BAFF, and APRIL. Therefore, interactions between TSLP in FDCs and IgA production in tonsils may be an important mechanism contributing to the pathogenesis of IgAN.