Prednisolone inhibits an IgE-mediated late-phase allergic cutaneous reaction by interfering with the activation of mast cells in mice

Epicutaneous antigen challenge in passively sensitized mice with IgE produc es a biphasic cutaneous response which peaks 1 h (immediate-phase reaction) and 24 h (late-phase reaction; LPR) after the antigen challenge. In this m odel, anaphylactic degranulation and interleukin 6 (IL-6) expression betwee n 4 and 8 h are observed in resident mast cells as the preceding stage of L PR. Prednisolone at a dose of 3 mg kg(-1) clearly inhibited the LPR when ad ministered 2 h before and 4 h after antigen challenge, Slight or no inhibit ion of LPR was observed by prednisolone administered 6-12 h after challenge . Histologically, prednisolone treatment 2 h before antigen challenge compl etely inhibited edema and inflammatory cell infiltration, while treatment a t 6 h did not at all. In order to investigate the relationship between inhi bition of LPR by prednisolone and mast cell activation, the effects of pred nisolone on degranulation of mast cells and IL-6 expression in mast cells w ere investigated. 8 h after antigen challenge, prednisolone clearly inhibit ed the increase in the number of anaphylactic degranulated and IL-6-positiv e mast cells by administration 2 h before challenge, but did not affect it by administration 6 h after challenge. These data indicate that the inhibit ory mechanism of prednisolone on LPR, at least, involves the inhibition of mast cell activation before LPR. Copyright (C) 2001 S. Karger AG, Basel.