Maintenance and amplification of cell-associated immunological memory in in vivo culture system

By employing bovine serum albumin as antigen and the capsular polysaccharide of Klebsiella pneumoniae as adjuvant, maintenance and amplification of immunological memory were analyzed in an in vivo culture system in mice. For this purpose, the double cell transfer technique was employed to minimize the influence of regulatory factors on memory expression. Memory associated with primed cells is maintained at the original level during in vivo culture for at least a month in the absence of antigen. In contrast, memory is amplified more than 30 times during this period by stimulation with antigen. This secondary increase in memory does not require the action of adjuvant. Neither the residual primary antigen nor preformed primary antibody seems to play a significant role in the maintenance and amplification of memory of the primed cells. From these results it is probable that the enduring immunological memory in actively immunized mice is conveyed by long-lived memory cells, and additional antigenic stimulating on once-established memory cells serve to amplify (not simply to maintain) memory in a secondary fashion.