Secondary delayed type hypersensitivity to sheep red blood cells in mice: Dependence on long-lived memory cells

Secondary delayed type hypersensitivity (DTH) to sheep red blood cells (SRBC) in mice is a long-lived memory phenomenon which is characterized by the accelerated reappearance of the state of DTH after a booster injection of the antigen. In this paper the nature of the DTH-related T memory cells accounting for secondary DTH was investigated. Parabiosis of primed and nonprimed mice for a period of 4 weeks resulted in an equally large secondary DTH responsiveness in both partners. This ability was maintained in both members for at least 6 months after termination of the parabiosis. These results indicate that (a) DTH-related T memory cells are potentially circulating cells, and (b) the persistence of these memory cells is not dependent on the presence of the antigen which induced their generation. Subcutaneous (sc) injection of intravenously (iv) primed mice with a small dose of antithymocyte serum before boosting did prevent the development of secondary DTH responsiveness in sc boosted mice, but not in iv boosted mice. Treatment of primed mice with vinblastine or azathioprine did not decrease the capacity of adoptive transfer of secondary DTH by means of spleen cells, but passive transfer of secondary DTH was completely abolished by this treatment. These results suggest that (a) SRBC-induced DTH-related T memory cells are nonproliferating, partially sessile, partially recirculating cells, and (b) these memory cells proliferate before they become DTH-related effector cells.