Development of animal models for cutaneous eosinophilic inflammation and analysis of its regulatory mechanisms

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Recent studies suggest that mast cell derived-TNF-alpha plays important roles in the development of contact hypersensitivity induced by hapten. Recently, we revealed that Fc epsilon RI beta-chain controls production of proinflammatory cytokines including TNF-alpha from mast cells through function of three tyrosine residues (Y219/Y229/Y225) of its ITAM. In the present study, we investigated the biological functions of mast cells expressing wild-type or mutated β-chain ITAM in development of the contact hypersensitivity employing mast cell "knock-in" mice.We prepared mast cells harboring wild-type (YYY) or Fc epsilon RI beta-chain ITAM mutant (FFF) by employing a retrovirus-mediated gene transfer into BMMCs derived from Fc epsilon RI beta-chain -/- mice. Those mast cells were intradermally transferred into ears of mast cell deficient mice (W/Wv). The mice were pre-sensitized by application of 2% oxazolone to the shaved abdomen. On day 5, 1% oxazolone and vehicle were applied to both sides of right ear and left ear, respectively. Contact hypersensitivity was evaluated by ear thickness.Cytokine expression in the tissue was analyzed by Real-Time PCR.As a result, oxazolone failed to cause ear swelling in W/Wv and Fc epsilon RI beta-chain -/- mice. In addition, we showed that ear swelling is significantly reduced in the FFF-knock-in mice as compared with that of YYY- knock-in mice. Consistent with this result, infiltration of CD3^<+> T cells and eosinophils into the inflammation sites was severely reduced in FFF-knock-in mice. Furthermore, an experiment using real-time PCR demonstrated that expression of TNF-alpha mRNA is also decreased in the ear tissue of FFF-knock-in mice. Taken together, these results suggest that regulation of mast cell activation through Fc epsilon RI beta-chain is critical for development of contact hypersensitivity following cutaneous exposure of hapten.