Suppressor cells in different types of unresponsiveness to DNCB contact sensitivity in guinea-pigs.

Cyclophosphamide (CY) treatment known to enhance the normal cell-mediated immune response by selectively inhibiting the function of suppressor cells abrogates tolerance by pretreatment when tolerant animals are sensitized 3 days after the intraperitoneal injection of CY. The tolerance during the primary response is also reversed by CY treatment, indicating that in both these types of unresponsiveness suppressor cells may be operating. However, CY treatment did not influence the short-lasting unresponsiveness induced in already sensitized guinea-pigs by the intravenous injection of tolerogen. These findings corroborate the idea that the mechanism of desensitization is different from that of tolerance induced by pretreatment of during the primary response.