Effect of FK 506 in the treatment of autoimmune glomerulonephritis in Brown Norway rats

Mercuric chloride (HgCl2) induces a lymphoproliferative disorder and autoimmune glomerulonephritis in Brown Norway (BN) rats. The effects of a new immunosuppressant, FK 506, on this model of glomerulonephritis were studied. BN rats were treated with HgCl2 according to a standard protocol (HgCl2 1 mg/kg s.c. 3 times/week). FK 506 was inoculated subcutaneously daily from day 15 to day 28. Animals were divided into 4 groups: group 1, rats were treated with normal saline alone and sacrificed on day 28; group 2, rats were treated with HgCl2 alone and sacrificed on day 14; group 3, rats were treated with HgCl2 alone and sacrificed on day 28, and group 4, rats were treated with HgCl2 and FK 506 (from day 15 to day 28) and sacrificed on day 28. Rats developed proteinuria by day 7, which reached a plateau level by day 14. On day 14, renal histology showed prominent mesangial cellular proliferation and the expansion of mesangial matrix. Electron microscopic study showed the effacement of visceral epithelial foot processes and the microvillous transformation of the visceral epithelium. Immunofluorescence study showed strong linear staining for IgG and the adhesion molecule ICAM-1 in all glomeruli. Treatment with FK 506 (1 mg/kg s.c. daily) resulted in a remarkable reduction in proteinuria on day 28 (493.5 +/- 48.3 vs. 24.4 +/- 13.5 mg/day) and an improvement in the morphological lesions. These findings suggest that FK 506 could be useful in the treatment of some human glomerulonephritides.