Background. We studied the effect of FK506 ointment on rat skin allogr
aft survival. Methods. Lewis rat (RT1(1)) skin allografts were histolo
gically evaluated on day 9 after transplantation to recipient ACI (RT1
(a)) rats. We set histological gradings for rejection as follows: grad
e 1, intraepidermal blister forrmation; grade 2, incomplete epidermal
separation from the dermis; and grade 3, complete epidermal separation
from the epidermis, According to these histological criteria, the imm
unosuppressive effect of FK506 ointment was assessed. Results. Our dat
a indicated that all recipient rats without FK506 ointment showed grad
e 3 rejection on day 7 after transplantation. In contrast, the allogra
fts treated with FK506 ointment showed grade 1 rejection. Furthermore
the blood concentration of FK506 was below 0.5 ng/ml, minimizing the s
ystemically adverse effects of FK506. Conclusions. Thus, the present s
tudy suggests that the topical administration of FK506 on the skin all
ografts may be useful and effective in the suppression of skin allogra
ft rejection.