The persistence of memory: a unique niche for IgG memory B cells.

T he concept of immunologic memory has been documented since ancient times. Indeed, in 450 BC, the Greek historian Thuydices observed that those who had survived a disease were most apt to visit the newly stricken, because “[they] knew it was from experience, and had now no fear for themselves, for the same man was never attacked twice.” Despite this longstanding appreciation, the mechanisms responsible for immunologic memory have proven elusive. This is particularly true for the mediators of humoral immunity, B lymphocytes.