Studies on the effect of systemic administration of sensitizers in guinea-pigs with contact sensitivity to inorganic metal compounds. I. The induction of immunological unresponsiveness in already sensitized animals.

A permanent state of specific immunological unresponsiveness can be produced in guinea-pigs already sensitive to K2Cr2O7 by a combination of the intravenous injection of 20 mg/kg K2Cr2O7 and an epicutaneous test with this compound given 24 hr after the intravenous injection. The later the first epicutaneous skin test after the intravenous injection is delayed, the shorter the period of unresponsiveness. An intravenous injection of less than 20 mg/kg also produces only a temporary state of desensitization. The time that animals became resensitized was proportional to the dose of K2Cr2O7 given intravenously. Intravenous injection of Be lactate into guinea-pigs sensitive to BeF2 produces only a temporary desensitization lasting no longer than 48 hr. It is suggested that the state of permanent unresponsiveness induced to K2Cr2O7 after the animals have already been made sensitive is an example of `high zone' immunological tolerance.