The properities of lymphocytes which carry immunologic memory of phiX 174

Cells that carry immunologic memory of phiX 174 have been studied in the rat. Memory cells could not be detected in thoracic duct lymph before the 10th day after priming. Thereafter, they increased rapidly in number to reach a plateau by the 4th week. This long latency was not due to a protracted process of maturation of cells formed and delivered to the lymph during the early post-induction period because memory never appeared in rats immunized adoptively with cells obtained before the 11th day. The fact that phiX memory cells are resistant to inhibition by vinblastine also indicates that memory is carried by cells which are released from regionally stimulated lymphoid tissue only after they have ceased dividing and become functionally mature. Adoptively acquired memory decays rapidly at first, but slowly from the 2nd week after cell transfer. This suggests that two cell populations of differing half-life are involved. If two distinct populations are necessary to the full expression of phiX memory, both populations recirculate because the memory cells in lymph draining the sites of the primary response and those reaching the central lymph of adoptive hosts give parallel dose-response curves.