Role of mast cells in the onset of IgE-mediated late-phase cutaneous response in mice

Background: In mice that are passively sensitized to IgE, cutaneous antigen challenge produces a biphasic response with peaks at 1 and 24 hours after challenge. Objective: We investigated the role of mast cells in the IgE-mediated late- phase reaction in mice. Methods: We histologically and ultrastructurally investigated the morpholog ic changes of mast cells during the biphasic responses. Results: Degranulation of mast cells, which was observed between 4 and 24 h ours after challenge, reached a peak at 8 hours. Piecemeal degranulation wa s seen during the immediate phase reaction. The number of IL-6-positive mas t cells was increased after 4 hours in both IgE-sensitized and unsensitized mice, but positive cells showed a greater increase in sensitized mice and reached a peak after 8 hours. With in situ hybridization experiments, mast cells were positive for IL-6 messenger RNA at 6 hours after challenge. Conclusion: These findings indicate that anaphylactic degranulation of mast cells and the expression of IL-6 mRNA within 4 hours after antigen challen ge are important for the onset of the late-phase allergic cutaneous reactio n in mice.