Analysis of the Consolidation Phase of Immunological Memory within the IgG Response to a B Cell Epitope Displayed on a Filamentous Bacteriophage.

Immunological memory can be defined as the ability to mount a response of greater magnitude and with faster kinetics upon re-encounter of the same antigen. We have previously reported that a booster dose of a protein antigen given 15 days after the first dose interferes with the development of memory, i.e., with the ability to mount an epitope-specific IgG response of greater magnitude upon re-encounter of the same antigen. We named the time-window during which memory is vulnerable to disruption a "consolidation phase in immunological memory", by analogy with the memory consolidation processes that occur in the nervous system to stabilize memory traces. In this study, we set out to establish if a similar memory consolidation phase occurs in the IgG response to a B cell epitope displayed on a filamentous bacteriophage. To this end, we have analyzed the time-course of anti-β-amyloid IgG titers in mice immunized with prototype Alzheimer's Disease vaccine fdAD(2-6), which consists of a fd phage that displays the B epitope AEFRH of β -amyloid at the N-terminus of the Major Capsid Protein. A booster dose of phage fdAD(2-6) given 15 days after priming significantly reduced the ratio between the magnitude of the secondary and primary IgG response to β-amyloid. This analysis confirms, in a phage vaccine, a consolidation phase in immunological memory, occurring two weeks after priming.