CD8+ T cells are the effectors ob the contact dermatitis induced by urushiol in mice and are regulated by CD4+ T cells

Background: The exposure of human skin to leaves and branches of litre (Lit hraea caustica), a Chilean endemic tree, induces a severe contact dermatiti s characterized by swelling and pruritus in susceptible individuals. The al lergenic priniciple of litre is 3-pentadecyl (10-enyl) catechol (litreol), which is structurally similar to the allergens isolated from poison oak and poison ivy. All of them belong to a family of compounds named urushiols. A s a proelectrophilic allergen, litreol must be intracellularly activated be fore modifying proteins of individuals exposed to it. As a result, self-pep tides derived from litreol-modified intracellular proteins would be present ed in the context of class I MHC molecules. We hypothesized that CD8+ T lym phocytes would play a major role during the effector phase of the immune re sponse induced by those modified peptides. in order to test this hypothesis , we investigated the cellular immune response to litreol in BaIb/cJ mice. The role of the different lymphocyte subpopulations in this response was as sessed by immunodepleting mice of CD4+ or CD8+ T lymphocytes using specific monoclonal antibodies (mAbs). We report the observation that the contact d ermatitis induced by litreol has two components: a primary response which d oes not require TCRalpha beta+ T cells, and a secondary response mediated m ainly by CD8+ T cells and regulated by CD4+ T cells. Our results show that CD8+ lymphocytes play a central role as effecters of the secondary response to litreol. Furthermore, our data suggest that two functionally different CD4+ T subpopulations serve as regulators of the CD8+ T cell function: a CD 4+ T helper population sensitive to a low dose of the depleting mAb, and CD 4+ T suppressor population which is eliminated only with a high dose of dep leting mAb.