CD70 and Th17 are involved in human contact sensitivity.

CD70 (CD27L) has been shown to be preferentially expressed on Th1, but not Th2, CD4+ lymphocytes in murine contact sensitivity. The CD70-CD27 co-stimulatory pathway as well as the Th17 subset of lymphocytes have also been identified in human contact sensitivity reactions. The authors have previously reported increased expression of CD70 and the Th17-specific transcription factor retinoid orphan receptor gamma T in the elicitation phase of allergic contact dermatitis by reverse transcriptase-polymerase chain reaction. The manipulation of these pathways has potential for ameliorating autoimmune and inflammatory disorders such as allergic contact dermatitis, psoriasis and rheumatoid arthritis. Also, upregulation of the CD70-CD27 and Th17 pathways has been associated with the remarkable ability of topical sensitizers to treat warts and skin cancers including melanoma. As natural killer and natural killer T cells are also involved in contact sensitivity, future studies investigating the function of these cells are necessary to elucidate the transition between innate and acquired immune responses in the context of the Th1/Th2/Th17 and regulatory T cell paradigm.