Amplification of cell-associated immunological memory by secondary antigenic stimulus. Secondary type increase in memory.

In mice primed with a mixture of bovine serum albumin (BSA) and adjuvant (capsular polysaccharide of Klebsiella pneumoniae (CPS-K)) cell-associated immunological memory was increased secondarily after a second injection of BSA alone, whereas a primary injection of BSA alone into normal unprimed mice did not result in detectable memory. The optimum antigen doses for expression of the primary and secondary memories of adoptively transferred cells from unboosted primed donors or boosted donors in in vivo culture systems were very similar, although those observed in intact mice were very different, as reported previously. The size of the secondary memory of adoptively transferred cells from boosted donors was more than ten times greater than that of the primary memory of adoptively transferred cells from unboosted primed donors. The lag period for increase of the secondary memory was shorter than that for the primary memory. Both primary and secondary memories increased during a long period (up to 3 months) after the antigenic stimulus. From the results of this study it was concluded that cell-associated immunological memory could be amplified in a secondary fashion upon contact with a second stimulus.