(a) MUTZ-3 and (b) THP-1 myeloid cell lines were cultured for 24 hours in the presence of vehicle (DMSO), the irritant SDS at 200 μM, the sensitizer dinitrochlorobenzene at 3.75 μM or PAP-1 at 10, 20, or 40 μM. CD86 expression was then measured by flow cytometry. Values are given as a stimulation index (SI), which is the ratio of CD86 expression of treated cells over CD86 expression of DMSO-treated cells (SI = (% of cells expressing CD86+ ×mean fluorescence intensity of CD86+ cells) of treated/(% of cells expressing CD86+ ×mean fluorescence intensity of CD86+ cells) of control). The values are the average±SEM of two independent experiments.