Studies on the induction of immunological tolerance by antigen in guinea-pigs already sensitized to dinitrochlorobenzene.

When guinea-pigs showing a high degree of contact sensitivity to dinitrochlorobenzene (DNCB) were injected intravenously with a related hapten, dinitrobenzene sulphonic acid sodium salt (DNBSO3), the animals became totally unresponsive for 1 to 4 days and remained thereafter in a state of diminished sensitivity, lasting for 8 weeks. No lasting total unresponsiveness was achieved by an additional intradermal injection of DNCB (or various variations thereof) performed 6 hr after the intravenous injection (`double shot' procedure), in contrast to what had been observed in the Neoarsphenamine and potassium dichromate system. The effect of the intravenous injection of DNBSO3 is attributed to a temporary disappearance of the sensitized lymphoid cells from the circulation, whereas the induction of a permanent unresponsiveness certainly requires some additional mechanism.