Glomerular Properdin Deposition Suggests a Favorable Therapeutic Response to Tonsillectomy and Steroid Pulse Therapy in IgA Nephropathy.

Background Glomerular properdin deposition in IgA nephropathy (IgAN) indicates alternative pathway activation and is associated with severe histological activity. However, its impact on the therapeutic response to tonsillectomy combined with steroid pulse therapy (TSP) remains insufficiently elucidated. Methods We retrospectively evaluated 28 patients with primary IgAN who completed the TSP protocol. Patients were classified into properdin-positive (P+, n = 17) and properdin-negative (P-, n = 11) groups. We compared baseline clinicopathological features and clinical outcomes at one year, including clinical complete remission (CR) rates. Results At baseline, there were no significant differences in clinical parameters, including urinary protein and estimated glomerular filtration rate, between the two groups. However, histologically, the P+ group tended to present with more severe active inflammatory lesions, such as higher histological grades and more frequent crescent formation. One year after TSP, both groups showed significant reductions in urinary protein. Notably, despite their severe histological presentation, the P+ group achieved a median urinary protein reduction of -85.4% and a clinical CR rate of 58.8%, which were statistically equivalent to those in the P- group (-68.6% and 63.6%, respectively). Conclusions Although glomerular properdin deposition reflects severe active histological lesions in IgAN, it also indicates complement-driven acute inflammation that is highly susceptible to intensive immunosuppression. TSP effectively suppresses this properdin-associated tissue injury, achieving favorable clinical outcomes regardless of histological severity. Properdin evaluation may assist in positioning TSP as a highly cost-effective first-line strategy.