CD1d restricted natural killer T cells are not required for allergic skin inflammation

Background: Invariant T-cell receptor-positive natural killer (iNKT) cells have been shown to be essential for the development of allergen-induced airway hyperreactivity (AHR). Objective: We examined the role of iNKT cells in allergic skin inflammation using a murine model of atopic dermatitis (AD) elicited by epicutaneous sensitization with ovalbumin (OVA). Methods: Wild-type (WT) and natural killer T-cell-deficient CD1d(-/-) mice were epicutaneously sensitized with OVA or normal saline and challenged with aerosolized OVA. iNKT cells in skin and bronchoalveolar lavage fluid were analyzed by fluorescence-activated cell sorting, and cytokine mRNA levels were measured by quantitative RT-PCR. AHR to methacholine was measured after OVA inhalation. Results: Skin infiltration by eosinophils and CD4(+) cells and expression of mRNA encoding IL-4 and IL-13 in OVA-sensitized skin were similar in WT and CD1d(-/-) mice. No significant increase in iNKT cells was detectable in epicutaneously sensitized skin. In contrast, iNKT cells were found in the bronchoalveolar lavage fluid from OVA-challenged epicutaneously sensitized WT mice, but not CD1d(-/-) mice. Epicutaneously sensitized CD1d(-/-) mice had an impaired expression of IL-4, IL-5, and IL-13 mRNA in the lung and failed to develop AHR in response to airway challenge with OVA. Conclusion: These results demonstrate that iNKT cells are not required for allergic skin inflammation in a murine model of AD, in contrast with airway inflammation, in which iNKT cells are essential. Clinical implications: Understanding the potential role of iNKT cells in AD will allow us to have a more specific target for therapeutic use.