Attempts to identify the causative allergen in cases of allergic contact dermatitis using an in vitro lymphocyte...

The use of an in vitro lymphocyte transformation test for the identification of the causative allergen in cases of human allergic contact dermatitis is described. Peripheral blood mononuclear cells (PBMC) were prepared from the venous blood of seven nickel-sensitized (patch test-positive) patients and ten non-sensitized control donors, and induced proliferation was measured by [(3)H]thymidine incorporation following culture for 7 days in the presence of various concentrations of nickel sulphate. Nickel sulphate is non-specifically mitogenic for human lymphocytes and although PBMC from all donors exhibited a significant increase in proliferation with nickel sulphate concentrations of 20 mug/ml, those isolated from Ni-sensitive patients responded to lower concentrations of the allergen. Employing a stimulation index of 3 following culture with 5 mug NiSO(4)/ml as an arbitrary indicator of specific proliferative responses to nickel, it was possible, using the lymphocyte transformation test, to separate Ni-sensitive from non-sensitized donors. In a limited series of experiments it was observed that lymphocytes prepared from each of two patients sensitized to neomycin sulphate mounted significant proliferative responses to this allergen in vitro; neomycin sulphate failed to induce similar changes in PBMC from non-sensitized donors. Finally, PBMC from one of two 2,4-dinitrochlorobenzene-sensitized donors were found to respond to autologous cells bearing the relevant dinitrophenol hapten.