Epicutaneous induction of hyporeactivity in contact sensitization. Demonstration of suppressor cells induced by contact with 2,4-dinitrothiocyanatebenzene.

Partial unresponsiveness to 2,4-dinitrofluorobenzene (DNFB) was produced by the epicutaneous application of 2 per cent 2,4-dinitrothiocyanatebenzene (DNTB) to the dorsum of the ear, 14 and 7 days before sensitization. This state of partial unresponsiveness could be broken by treatment with 300 mg/kg cyclophosphamide (CY) 3 days before the sensitization dose of DNFB. There was a significant increase in the uptake of 125I-labelled iododeoxyuridine in the draining lymph node, 6 days after the application of 2 per cent DNTB and in the contralateral nodes at 4 and 6 days. The state of partial unresponsiveness to DNFB was not associated with a decrease in T-cell proliferation in the draining lymph nodes. The generation of suppressor cells, capable of reacting in the periphery, was demonstrated by passive cell transfer into recipients sensitized to DNFB and depleted of normally produced suppressor cells by pretreatment with CY. These cells were found in spleen and peritoneal exudates of animals treated by the epicutaneous application of 2 per cent DNTB 14 and 7 days previously. It is suggested that the suppressor cells induced by contact with DNTB act by competition with effector cells at the periphery.