Effects of 0.1% tacrolimus on canine skin mast cells and eosinophils

Five dogs were used to determine whether 0.1% tacrolimus ointment application for one day would inhibit IgE-mediated late-phase reactions (LPRs). It was consisted of three periods: One period without therapeutic administration (control) and two periods of treatment with either the tacrolimus ointment or vehicle. Induction of IgEmediated LPRs was induced by intradermal injections of 0.05 ml (0.14 mg/ml) of solution of goat anti-canine IgE polyclonal antibodies. Each section for mast cells (MCs) and eosinophils (EPs) was stained with acidified toluidine blue, and Luna's stain, respectively. Assessment of anti-inflammatory effect of tacrolimus ointment composed of cell counts of MC and EP from lesions of induced LPR. In normal canine biopsies, the number of dermal MCs and EPs were 12.3 ± 1.4 cells/mm² and 3.1 ± 1.3 cells/mm², respectively. MC counts dramatically decreased at time dependent manner after anti-IgE administration. However, the number of MCs on 6 hours after challenge was significantly less decreased in the groups treated with the tacrolimus, as compared with control and vehicle group. The number of EPs on 24 hours after challenge was significantly lower in the group treated with the tacrolimus than in the control and vehicle groups. In conclusion, this study revealed that 0.1% tacrolimus ointment in dogs may exert a potent antiinflammatory effect on inhibition of MC degranulation and also secondary prevention of EP infiltration during LPR.