The purpose of this study is to identify invariant natural killer T cells (NKT cells) in cellular infiltrate of human
allergic contact dermatitis (ACD) skin challenge sites. Skin biopsy specimens were taken from positive patch test reactions from 10 different patients (9 different
allergens) and studied by immunochemistry, real-time PCR, nested PCR, and in situ hybridization to identify NKT cells and the
cytokines associated with this cell type. Invariant NKT cells were identified in all the 10 skin biopsy specimens studied, ranging from 1.72 to 33% of the cellular infiltrate. These NKT cells were activated in all cases, as they expressed
cytokine transcripts for IFN-gamma and
IL-4. Invariant NKT cells are present in ACD, regardless of the
allergen that triggers the reaction, and are in an activated state. We conclude that innate immunity plays a role in late phases of
type IV hypersensitivity reactions and may be responding to self-
lipids released during allergic
inflammation. These data
complement the previous work by other investigators that suggest that NKT cells are important in the early cellular response during primary immune responses to
allergens. Herein, it is demonstrated that NKT cells are constantly present during the late elicitation phase of human
type IV hypersensitivity reactions.