The hair dyes PPD and PTD fail to induce a T(H)2 immune response following repeated topical application in BALB/c...

1,4-Phenylenediamine (PPD) and the structurally-related 1,4-toluenediamine (PTD) are frequently used oxidative hair dye precursors that can induce a delayed-type hypersensitivity reaction known as contact allergy. Very rare cases of Type 1 (IgE-mediated) allergic responses associated with PPD or PTD have been reported among hair dye users. As part of an effort to determine if repeated dermal exposure to the dyes could induce a T-helper-2 (T(H)2) response, we used a dermal exposure regimen in mice reported to identify a T(H)2 response. Ear swelling was evident at post-final exposure to PPD and PTD, indicating that an immune response was observed. However, cytokine mRNA after repeated topical exposure to these two chemicals showed no shift in the expression toward the typical T(H)2 cytokines interleukin (IL)-4 and IL-10 compared to the T(H)1 cytokine interferon (IFN)-γ. Consistent with these cytokine profiles, no concomitant increase in total serum IgE antibody titer or in B220+IgE+ lymphocytes in lymph nodes and skin application site skin was detected. In contrast, using an identical exposure regimen, animals topically exposed to the known respiratory (Type 1) allergen toluene 2,4-diisocyanate (TDI) showed significant expression of IL-4 and IL-10 mRNA compared to IFN? as well as an increase in total serum IgE and in B220+IgE+ cells in lymph nodes and skin application site. The data generated are consistent with the pattern of adverse reactions to hair dyes seen clinically, which overwhelmingly is of delayed rather than immediate-type hypersensitivity. Although current animal models have a limited ability to detect rare T(H)2 responses to contact allergens, the present study results support the view that exposure to hair dyes is not associated with relevant T(H)2 induction.