Acute tubulointerstitial nephritis : phenotype of infiltrating cells and prognostic impact of tubulitis

The prognostic impact of tubulitis and the phenotype of the infiltrating cells in the tubules were studied in ten percutaneous renal biopsies from six patients with acute tubulointerstitial nephritis (ATIN). The inflammatory cell subsets in the tubules and interstitium (CD3+, CD4+, CD8+, CD20+, CD45RO+, CD56+, CD57+, CD68+ and TIA-1+ cells), the expression of vimentin and the proliferation-associated antigen Ki-67 by cortical tubular cells, and the grade of tubulitis, interstitial infiltration and fibrosis were analysed. Cytotoxic injury to tubular cells in the vicinity of tubular-wall-localized lymphocytes was studied ultrastructurally. ATIN was drug-induced in three patients, related to Legionella infection in two and idiopathic in one patient. Four patients recovered, one with reduced renal function. Two patients developed end-stage renal disease. CD8+ and CD4+ lymphocytes, and a smaller number of macrophages, infiltrated the tubules. The predominant lymphocyte subset in the tubules was the same as in the interstitium. Cytotoxic injury to tubular cells was not seen electron microscopically. The tubular cells exhibited increased proliferative activity and expressed vimentin, indicating non-specific tubular damage. The cell subset, the severity of tubulitis, and the tubular expression of vimentin were not related to outcome. The main prognostic factor was the severity of the interstitial fibrosis. Tubulitis in ATIN may be a harmless non-immune reaction, mediated by tubular expression of cytokines, together with adhesion and other molecules.