Nickel-induced proliferation of both memory and naive T cells in patch test-negative individuals

Lymphocyte transformation test has often been used as an in vitro test for nickel allergy. We have previously demonstrated the presence of nickel-reac tive T cells in individuals with no history of allergic disease and with a negative patch test towards NiSO4. In this study, we show that this prolife rative response was mainly confined to T cells within the CD4(+) subset. In contrast to conventional recall antigens such as tetanus toroid, in vitro stimulation using NiSO4 activated both FACS-purified CD4(+)CD45RA(+) 'naive ' and CD4(+)CD45RO(+) 'memory' T cells. To determine which cell population reacted with nickel to induce T cell activation, peripheral blood mononucle ar cells were separated into macrophages and non-adherent, HLA-DR-depleted T cells. We found that preincubation of monocytes/ macrophages but not T ce lls with NiSO4 resulted in subsequent T cell proliferation. This result dem onstrated that nickel did not exhibit any direct effect on the T cell. Furt hermore, the NiSO4-induced T cell proliferation could be blocked by antibod ies towards MHC class II (HLA-DR) molecules. Our results substantiate the c oncept that individuals with a negative patch test towards NiSO4 contain in their peripheral blood T cells capable of recognizing nickel or nickel-mod ified peptides. In contrast to conventional recall antigens, both memory an d naive T cells were activated. Thus, when compared with data obtained from nickel-allergic individuals, this study shows a comparable nickel-inducibl e T cell activation in non-allergic individuals.