In 1965 Epstein and Maibach sensitized 13 psoriasis patients and 32 healthy controls with the strong allergen DNCB and found a slightly reduced sensitization ratio in the psoriatic group, but interpretation was hampered by the small study sample [15]. Two other experimental studies sensitizing psoriatic patients with DNCB have been conducted. Both studies used a high allergen dose for sensitization, sensitizing almost all participants, and hence they focused on the degree of challenge responses only. Moss et al. found reduced challenge reactions compared to healthy controls [5], and Obalek and co-workers reported a higher threshold in psoriasis patients compared to healthy

controls [6]. These results strongly suggest changes Imatinib supplier in the elicitation phase of sensitization among psoriatic patients. We only found a trend towards reduced reactivity in challenge responses. This might be due to the use of a different allergen or, more probably, that the effect is dependent upon the sensitization dose, which in our study was deliberately chosen to be relatively low, sensitizing only 65% of the healthy group in order to study the differences in sensitization potentials. A low sensitization ratio

of patients with diabetes type I compared with healthy controls was found in our Autophagy inhibitor libraries study, although on the border of statistical significance. One study has demonstrated a reduced sensitization ratio in patients with rheumatoid arthritis using DNCB [7], indicating that the impaired reactivity to hapten could be common for autoimmune diseases. The autoimmune diseases psoriasis, diabetes type I, rheumatoid arthritis and inflammatory bowel Thiamet G disease have been linked through common clinical traits, genetic polymorphisms and immunological pathways [16–18]. Theoretically, it seems likely that the autoimmune diseases share an immunological milieu that can interfere with the expression of a contact allergic response. In contact allergy an individual becomes sensitized to a hapten, a low molecular weight chemical, through a complex process involving integrated signals from the innate and adaptive immune system, in which during the induction phase T cells are

primed in lymphoid organs, and upon re-exposure to the hapten during the elicitation phase are recruited to the skin and mediate the clinical outcome of allergic contact dermatitis. In murine studies, regulatory T cells have been shown to play a regulatory role in reducing the magnitude of the elicitation responses and in preventing priming to haptens [19–21]. In humans, specific CD4+CD25+ regulatory T cells capable of inhibiting CD4+CD25- nickel-specific effector T cells in vitro have been demonstrated in allergen-challenged skin and blood of non-allergic individuals [8,9], indicating an active down-regulation. These findings led us to investigate the elicitation sites of the participants in our sensitization study for down-regulatory mechanisms.