Renal Tubular Lysozyme in Tubulointerstitial Diseases and Renal Sarcoidosis

Background: Tubulointerstitial diseases are one of the common features of kidney diseases. Histological characteristics include infiltration of inflammatory cells, tubular atrophy, and interstitial fibrosis. Causes of tubular damage vary, including drugs, systemic inflammatory diseases, genetic disorders, infections, ischemia, toxins, and sarcoidosis, however, differentiating based solely on specimen information is sometimes challenging. Methods: A total of 96 consecutive renal biopsy samples diagnosed with tubulointerstitial diseases between 2016 and 2023 at the Japan Community Health Care Organization Sendai Hospital were stained with lysozyme using immunohistochemistry. Each specimen was evaluated and classified as either lysozyme positive or negative. Results: Positive lysozyme staining was observed in 24 samples, including 13 cases of sarcoidosis-associated tubulointerstitial nephritis (TIN), one case of chronic myelomonocytic leukemia-associated lysozyme-induced nephropathy, one case of inflammatory cell infiltration in B-cell lymphoma, one case of ulcerative colitis-associated TIN, three cases of drug-associated TIN, and five cases of idiopathic TIN. Conclusion: The results provide evidence of the effectiveness of lysozyme immunohistochemistry against tubulointerstitial diseases in narrowing down the differential diagnosis or detecting underdiagnosed diseases. Notably, renal sarcoidosis can be detected with 100% accuracy. This finding suggests that lysozyme immunohistochemistry can be valuable for diagnosing sarcoidosis-associated TIN.