Persistent immune tolerance to nickel and chromium by oral administration prior to cutaneous sensitization

Oral administration of allergens, foreign proteins, or cell-bound antigens may induce systemic suppression of subsequent humoral and cell-mediated immune responses ("oral tolerance"). The induction of specific immune tolerance provides a potential strategy for treatment of T-cell-dependent immune diseases. Therefore, in depth studies into preconditions for optimal and persistent tolerance induction are mandatory. Here we report on such studies in a guinea pig model using the non-cross-reactive contact allergens nickel and chromium. Feeding per os of nickel sulfate or potassium dichromate did not trigger systemic TDTH-effector functions. Instead, short feeding periods led to a dose-dependent, and metal-specific, suppression of subsequently induced allergic contact hypersensitivity. Administration of the allergens onto the oral mucosa was most effective in the induction of immune tolerance. When first sensitizing attempts were delayed until 1 year after feeding, the degree of unresponsiveness was reduced. In contrast, with cutaneous contacts starting shortly after the feeding period, tolerance was fully stable and undiminished for at least 2 years. Thus, in orally treated guinea pigs cutaneous contacts provide boosting tolerogenic signals, supporting the view that oral tolerance does not result from clonal deletion but from active antigen-specific immunosuppression. Indeed, unresponsiveness to cutaneous immunization could be transferred by lymphoid cells from fed guinea pigs in a metal-specific way.