Enhanced epidermal Langerhans cell migration in IL-10 knockout mice.

The migration of epidermal Langerhans cells (LC) to lymph nodes (LN) is critical in the initiation of contact hypersensitivity (CHS) responses. Studies suggest that contact allergen-induced epidermal proinflammatory cytokines, including IL-1 and TNF-alpha, play important roles in promoting LC migration. Contact allergens also induce epidermal anti-inflammatory cytokines such as IL-10. Since IL-10 down-regulates proinflammatory cytokine production and inhibits CHS, we hypothesized that IL-10 might inhibit LC migration. To test this hypothesis, IL-10 knockout (KO) mice were epicutaneously sensitized with the hapten, FITC, and 24 h later hapten-bearing cells in the draining LN were examined. The number of hapten-bearing cells in the LN was significantly greater in IL-10 KO mice than in wild-type mice. The mutant mice also had an exaggerated CHS to FITC. Pretreatment with anti-TNF-alpha Ab or IL-1R antagonist significantly reduced the number of hapten-bearing cells in the LN, suggesting that IL-10 modulation of LC migration involves IL-1 and TNF-alpha. Moreover, IL-10 KO mice demonstrated a greater increase in TNF-alpha, IL-1alpha, and IL-1beta mRNAs in the allergen-exposed epidermis, and keratinocytes derived from the mutant mice were able to produce higher amounts of TNF-alpha and IL-1alpha protein. These data suggest that IL-10 plays an inhibitory role in LC migration and that this effect may occur via the down-regulation of TNF-alpha and IL-1 production.