Epithelial inclusions and Tamm-Horsfall protein in paranephric lymph nodes. A light microscopy and immunocytochemical study.

An unusual histological pattern made up of tubular structures and clusters of apparently epithelial cells floating within sinusoidal deposits of Tamm-Horsfall (TH) protein was observed in several lymph nodes removed with renal tumours (3 Wilms' tumours, 1 cystic nephroma) and pathological but non neoplastic kidneys (2 cases of reflux nephropathy). Masses of TH protein, often containing desquamated tubular epithelial cells, were also found in tubules, interstitium and perivascular lymphatic vessels of the resected kidneys, but never in the tumour tissue. Lymph nodes draining renal tumours, although moderately enlarged because of reactive hyperplasia and TH protein deposits, did not contain metastases. Our findings suggest that these inclusions originate from renal tubular epithelium and are transported to paranephric lymph nodes along with TH protein.