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The T-helper 1/T-helper 2 (Th1/Th2) cell balance was examined in 6-month-old New Zealand black/white F1 (B/WF1) mice treated with an immunosuppressive agent, FK506. The survival rate of mice treated with 10 mg/kg/day of FK506 was 7/8, while that of those treated with 2.5 mg/kg/day was 5/8, and 4/8 after treatment for 8 weeks with placebo. Proteinuria, which was already positive in all mice before the treatment, in the seven of eight mice treated with 10 mg/kg/day remained mildly positive (≤1+), while seven of eight mice treated with 2.5 mg/kg/day and six of eight mice treated with the placebo showed severe proteinuria (≥2+). Pathological changes in the kidneys of mice treated with 10 mg/kg/day of FK506 were less severe than in mice treated with the placebo or 2.5 mg/kg/day of FK506. Expression of mRNA was unchanged for all cytokines determined in the groups treated with 2.5 mg/kg/day of FK506 or placebo. In contrast, expression of mRNA for interleukin (IL)-2, and interferon (IFN)-γ was suppressed, while that for IL-4 and IL-10 was not suppressed in the group treated with 10 mg/kg of FK506. The serum levels of IgG-class anti-DNA antibodies, which had been elevated before the treatment, were suppressed -- especially in the IgG2a subclass -- and the deposition of IgG2a and IgG2b in the glomeruli was reduced in the group treated with 10 mg/kg/day of FK506 compared with the other groups. These findings suggest that an improvement in the lupus nephritis of 6-month-old B/WF1 mice induced by FK506 might be associated with a predominant inhibition of Th1 cytokine. [ABSTRACT FROM AUTHOR]