Pyridinyl imidazoles inhibit the inflammatory phase of delayed type hypersensitivity reactions without affecting T-dependent immune responses.

The effects of pyridinyl imidazoles, specifically SK&F 105809 and its metabolite, on normal T-cell and B-cell mediated immune responses were examined and compared to the fungal macrolide immunosuppressives, cyclosporin A, FK506 and rapamycin and to the corticosteroid, dexamethasone. The orally active prodrug SK&F 105809 [2-(4-methylsulfinylphenyl)-3-(4-pyridyl)-6,7-dihydro-[5H]-pyrrolo [1,2-a] imidazole[ and its metabolite, SK&F 105561 [2-(4-methylthiophenyl)-3-(4-pyridyl)-6,7-dihydro-[5H]-pyrrolo[1,2 -a] imidazole] are dual 5-lipoxygenase (5-LO) and cycloxygenase (CO) inhibitors with potent anti-inflammatory and cytokine (IL-1/TNF) suppressive activities. The anti-inflammatory activity of SK&F 105809 and its metabolite were evaluated in an antigen-specific murine model of delayed type hypersensitivity (DTH) response, where they were found to affect only the inflammatory and not the induction phase of this response. In contrast, these compounds and other pyridinyl imidazoles (SK&F 86002 and its analog, SK&F 104351) exhibited no immunosuppressive activity under conditions where the macrolide rapamycin and the corticosteroid dexamethasone abrogated both the cellular and humoral immune responses. Thus, the ability of pyridinyl imidazoles to attenuate independently the inflammatory components of the disease without causing generalized immunosuppression enhances their profile as candidates for therapy of chronic inflammatory diseases, specifically those mediated by cytokines (e.g. IL-1, TNF) and eicosanoids.