Nano-titanium dioxide modulates the dermal sensitization potency of DNCB

We determined the ability of a model nanoparticle (NP) (titanium dioxide, TiO 2 ) to modulate sensitization induced by a known potent dermal sensitizer (dinitrochlorobenzene) using a variant of the local lymph node assay called lymph node proliferation assay. BALB/c mice received sub-cutaneous injections of vehicle (2.5 mM sodium citrate), TiO 2 NPs (0.004, 0.04 or 0.4 mg/ml) or pigment particles (0.04 mg/ml) both stabilized in sodium citrate buffer at the base of each ear (2x50μl), before receiving dermal applications (on both ears) of 2,4-Dinitrochlorobenzene (DNCB) (2x25μl of 0.1%) or its vehicle (acetone olive oil – AOO (4:1)) on days 0, 1 and 2. On day 5, the stimulation index (SI) was calculated as a ratio of 3 HTdR incorporation in lymphocytes from DNBC-treated mice and AOO-treated controls. In a second experiment the EC 3 -value for DNCB (0 to 0.1%) was assessed in the absence or presence of 0.04 mg/ml TiO 2 . In a third experiment, the lymphocyte subpopulations and the cytokine secretion profile were analyzed after TiO 2 (0.04 mg/ml) and DNCB (0.1%) treatment. Injection of NPs in AOO-treated control mice did not have any effect on lymph node (LN) proliferation. DNCB sensitization resulted in LN proliferation, which was further increased by injection of TiO 2 NPs before DNCB sensitization. The EC 3 of DNCB, with prior injection of vehicle control was 0.041%, while injection with TiO 2 decreased the EC 3 of DNCB to 0.015%. TiO 2 NPs pre-treatment did not alter the lymphocyte subpopulations, but significantly increased the level of IL-4 and decreased IL-10 production in DNCB treated animals. In conclusion, our study demonstrates that administration of nano-TiO 2 increases the dermal sensitization potency of DNCB, by augmenting a Th 2 response, showing the immunomodulatory abilities of NPs.