Inhibitory effects of FK506 on the development of experimental allergic/immune-mediated blepharoconjunctivitis in Lewis rats by systemic but not by topical administration

Background: FK506 has been used for treatment of cell-mediated immune disor ders such as graft rejection in transplantation or Behcet disease. To evalu ate the effectiveness of FK506 in another ocular disease model, we injected FK506 in rats with experimental allergic/immune-mediated blepharo conjunct ivitis (EAC) the induction mechanism of which depends on cell-mediated immu nity. Methods: Lewis rats were immunized with ovalbumin (OVA) in emulsion o f complete Freund's adjuvant (CFA). We injected 2 (n=6), 20 (n=6) or 200 (n =5) mu g of FK506 intramuscularly daily from the day of immunization (day 0 ) to day 6. Control rats were not treated with FK506 (n=4). In addition, we injected 200 mu g of FK506 from day 7 to day 13 (n=12) to compare the timi ng of FK506 administration (day 0 to day 6, n=12; control, n=12). Twenty-on e days after immunization, all rats were challenged with OVA by eye drops, and 24 h later they were killed after clinical evaluation and their eyes, b lood and draining lymph nodes were harvested for histology, antibody titers and proliferation assay or flow cytometric analysis. In another set of exp eriments, rats that had received OVA-primed lymph node cells did (n=9) or d id nor (n=9) receive additional FK506 by injection daily for 4 days. Four d ays after transfer, these rats were challenged with OVA and evaluated as me ntioned. To investigate possible suppression of disease by topical administ ration of FK506, both actively immunized and passively immunized rats recei ved OVA together with 0.3% (weight/volume) of FK506 (n=16) or vehicle (n=10 ) by eye drops and 24 h after challenge, rats were evaluated as mentioned. Results: Development of disease, induced by either active or passive immuni zation, was inhibited in the group treated with 200 mu g of FK506, regardle ss of timing of administration. Cellular proliferative responses to OVA wer e inhibited only in this group. Flow cytometry demonstrated a decrease of a bout 20% in the proportion of all cells made up by CD4-positive T cells. To pical administration of FK506 inhibited the development of EAC, though not significantly. Conclusions: Systemic treatment with 200 mu g of FK506 eithe r in the induction or the effector phase inhibits the development of EAC in Lewis rats. Topical administration is not so effective as systemic adminis tration.