Determination of in vivo dose response and allergen-specific T cells in subjects contact-sensitized to squaric acid dibutyl ester

Background. Squaric acid dibutyl ester (SADBE) is a known contact sensitizer, but dose-response data are not defined. Objective: To determine the relationship between sensitization dose and contact hypersensitivity (CHS) response to SADBE in human volunteers. The study also aimed to investigate whether SADBE-reactive blood T cells could be detected using ex vivo mature dendritic cells (DCs) as antigen-presenting cells. Method. Forty healthy volunteers were sensitized to either 12.5, 25, 50, or 250 mu g of SADBE in a 48 mu L volume. This was followed by elicitation 2 weeks later with five doses (0, 0.2, 2, 20, and 200 mu g in 20 mu L). An additional 10 subjects received the elicitation doses without prior sensitization. Blood samples obtained after sensitization were purified into T cells and mature DCs. Results: A direct relationship between sensitization dose and in vivo CHS response was observed. The SADBE dose that effectively sensitized 50% of the population (ED50) was 22 mu g/cm(2). Significant SADBE-specific T-cell proliferation in vitro was not observed 2 weeks after sensitization but became evident after elicitation. Conclusion: This study establishes the in vivo dose-response characteristics of immune reactivity to SADBE and antigen-specific T-cell reactivity.