p-Phenylenediamine (
PPD) and
Diphenylcyclopropenone (DPCP) are two potent
haptens. Both
haptens are known to cause delayed-type
hypersensitivity, involving a
cytokine response and local infiltration of T-cell subpopulations, resulting in
contact dermatitis. We investigated the systemic immune effects of
PPD and DPCP, two relatively unexplored skin
allergens. The dorsal sides of the ears of BALB/c mice were exposed to
PPD or DPCP (0.1% w/v or 0.01% w/v), or vehicle alone. Mice were treated once daily for 3 days (induction period) and subsequently twice per week for 8 weeks. Local and systemic immune responses in the auricular and pancreatic lymph nodes, spleen, liver, serum, and ears were analyzed with
cytokine profiling MSD, flow cytometry, and qPCR. Ear swelling increased significantly in mice treated with 1%
PPD, 0.01% DPCP or 0.1% DPCP, compared with vehicle treatment, indicating that the mice were sensitized and that there was a local
inflammation. Auricular lymph nodes, pancreatic lymph nodes, spleen, and liver showed changes in regulatory T-cell, B-cell, and NKT-cell frequencies, and increased activation of CD8(+) T cells and B cells. Intracellular
cytokine profiling revealed an increase in the IFN-γ- and IL-4-positive NKT cells present in the liver following treatment with both
haptens. Moreover, we saw a tendency toward a systemic increase in
IL-17A. We observed systemic immunological effects of
PPD and DPCP. Furthermore, concentrations too low to increase ear thickness and cause clinical symptoms may still prime the immune system. These systemic immunological effects may potentially predispose individuals to certain diseases.