In the second stage of the study, 20 subjects (Cohort 2) will be exposed to an immunosuppressive dose of ultraviolet B (UVB) 24 hours prior to DPCP sensitization. This is expected to result in the abolition of CHS upon rechallenge with DPCP. In order to assess whether denosumab can reverse UVB-induced immunosuppression, the subjects will have previously been randomized to receive a single 1mL injection of either 60 mg denosumab (group A; 10 subjects) or 1 mL saline (group B; 10 subjects) two weeks before UVB exposure. CHS reactions elicited by DPCP rechallenge will be compared between the denosumab and saline groups.