Decreased expression of follicular dendritic cell-secreted protein correlates with increased immunoglobulin A production in the tonsils of individuals with immunoglobulin A nephropathy.

Immunoglobulin A nephropathy (IgAN) is characterized by a qualitative abnormality of IgA in the circulation and IgA deposition in the renal mesangium. Recent research has indicated that pathogenic IgA may originate from affected tonsils. Follicular dendritic cell-secreted protein (FDC-SP), a small novel secretory protein that may regulate the induction of B-cell responses, has been suggested to control IgA production. Given this background, this study investigated the expression of FDC-SP and its correlation with IgA production in the tonsils of IgAN patients. Immunohistochemistry and reverse transcription-polymerase chain reaction were used to compare the expression of FDC-SP in the tonsils of IgAN patients with tonsillitis and of non-IgAN patients with chronic tonsillitis. The location of FDC-SP in tonsillar tissue was confirmed by double immunofluorescence. We found that FDC-SP expression significantly decreased and was correlated negatively with enhanced IgA production in the tonsils of IgAN patients. FDC-SP secreted by follicular dendritic cells may act on germinal center B cells and participate in the modulation of IgA generation in the tonsils. Our study demonstrated that FDC-SP may be involved in IgA production in the tonsils of IgAN patients, making this protein an attractive candidate immunomodulator, and highlighting a promising strategy for therapeutic intervention in IgAN.