Renal Interstitial Infiltration and Tertiary Lymphoid Organ Neogenesis in IgA Nephropathy

Background and objectives Previous studies have identified inflammatory features that enable the prediction of renal outcome of IgA nephropathy (IgAN); however, validation of these findings is still needed. This prospective study was performed to determine the characteristics of renal interstitial infiltration and tertiary lymphoid organ (TLO) neogenesis in a cohort of Chinese patients with IgAN. Design, setting, participants, & measurements Adult patients with IgAN were recruited into this study from June 2009 to June 2010. Inflammatory cells in renal biopsy tissues were detected by immunohistochemistry and immunofluorescence. Correlations between the density of interstitial inflammatory cells, grades of TLOs, and clinicopathologic features were evaluated. Of 152 eligible patients, 72 (47%) were successfully followed-up by telephone at 30 months after renal biopsy. Twelve patients were classified as the severe group and 60 patients were classified as the stable group, according to the progression of serum creatinine levels during the follow-up period. A comparison of the severity of interstitial infiltration and the frequency of TLO neogenesis between the two groups was performed. Results The accumulation of interstitial inflammatory cells was correlated with decreased renal function, heavy proteinuria, and severe glomerular, interstitial, and arterial lesions in patients with IgAN. TLOs, identified as nodular inflammatory infiltrates containing organized DC-SIGN+, CD4+, CD8+, and CD20+ cells, were observed in 37.5% of patients. Patients with high-grade TLOs exhibited a high percentage of mesangial hypercellularity and crescents as well as severe interstitial and arterial lesions. Patients in the severe group exhibited more severe interstitial infiltration and a higher percentage of TLO neogenesis (83.3% versus 33.3%; P=0.001) compared with patients in the stable group. Conclusions As contributors to an active local inflammatory response, the severity of interstitial infiltration and the frequency of TLO neogenesis are correlated with glomerular, interstitial, and arterial lesions as well as IgAN progression.