Detection and clinical usefulness of urinary interleukin-6 in the diseases of the kidney and the urinary tract.

Interleukin-6 (IL-6) plays a key role in inflammatory and immune responses in the host. In the present study, the IL-6 activity in urine from patients with various renal diseases was examined to elucidate the pathological and clinical significance of urinary IL-6. In patients with mesangial proliferative glomerulonephritis (mes-PGN) including, IgA nephropathy, the urinary IL-6 activity tended to increase with the progression of mesangial hypercellularity. In four patients with IgA nephropathy, urinary IL-6 activity increased markedly but transiently during episodes of acute exacerbation associated with upper respiratory tract infection. In addition, it was demonstrated that urine from patients with other types of PGN such as poststreptococcal acute glomerulonephritis and membrano-proliferative glomerulonephritis contained large quantities of IL-6. However, the levels of urinary IL-6 activity were almost within the normal range in non-proliferative glomerular diseases such as membranous nephropathy, minimal change nephrotic syndrome and lupus nephritis (WHO class I and V), non-glomerular bleeding and orthostatic proteinuria. It should be noted that a marked increase in urinary IL-6 was often observed in the patients with urinary tract infection. These results indicated that IL-6 in urine might be derived from various types of cells participating in inflammatory reactions not only in the renal parenchyma but also in the urinary tract.