Functional caspase-1 is required for Langerhans cell migration and optimal contact sensitization in mice

Langerhans cell (LC) migration from epidermis to draining lymph node is a critical first step in cutaneous immune responses. Both TNF-alpha and IL-1 beta are important signals governing this process, but the potential regulatory role of IL-1 alpha processing by caspase-1 is unknown. In wild-type (WT) mice, application of the contact allergens 2,4-dinitrofluorobenzine and oxazolone lead to a marked reduction in epidermal LC numbers, but in caspase-1-deficient mice this reduction was not observed. Moreover, although intradermal injection of TNF-alpha (50 ng) induced epidermal LC migration in WT mice, this cytokine failed to induce LC migration in caspase-1-deficient mice. Intradermal IL-1 beta (50 ng) caused a similar reduction in epidermal LC numbers in both WT and caspase-1-deficient mice, indicating that, given an appropriate signal, caspase-1-deficient epidermal LC are capable of migration. Contact hypersensitivity to both 2,4-dinitrofluorobenzine and oxazolone was inhibited in caspase-1-deficient mice, indicating a functional consequence of the LC migration defect. In organ culture the caspase-1 inhibitor Ac-YVAD-cmk, but not control peptide, potently inhibited the epidermal LC migration that occurs in this system, and reduced spontaneous migration of LC was observed in skin derived from caspase-1-deficient mice. Moreover, Ac-YVAD-cmk applied to BALB/c mouse skin before application of contact sensitizers inhibited LC migration and contact hypersensitivity in vivo. Taken together, these data indicate that caspase-1 may play a central role in the regulation of LC migration and suggest that the activity of this enzyme is amenable to control by specific inhibitors both in vivo and in vitro.