Figure 4.

  Kinetics of a prototypical serum antibody response. The kinetics of an antigen‐specific antibody response does not typically follow a single rate of decay but instead will often follow a pattern involving at least three phases of antibody half‐life kinetics. Shortly after the peak in antibody production following acute infection or vaccination, antibody responses will decline rapidly, often at the rate of free IgG protein catabolism and removal from the serum [T _1/2 = 17.5–26 days (74, 75, 76)]. For the next 1–3 years, antibody responses will be more long‐lived but will still decline more rapidly than antibody responses analyzed at >3 years after the antigenic insult when antibody production has reached steady‐state levels (1, 80). During the first 1–3 years after vaccination or infection, the antibody response may be maintained by a combination of memory B‐cell‐dependent mechanisms (e.g. persisting antigen on the surface of FDCs) and memory B‐cell‐independent mechanisms (i.e. long‐lived plasma cells), and in this case, the final, steady state antibody response would only become apparent once the antigen depot has been exhausted and is no longer contributing to the plasma cell pool. An alternative model that is not mutually exclusive to the persisting antigen model is that antibody responses elicited during the first few years after vaccination or infection may be produced by a mixed population of long‐lived and short‐lived plasma cells. Plasma cells with the shortest lifespan will decline over time, which will eventually select for the subset of plasma cells with the longest inherent lifespan. Bearing this in mind, the longevity of a given antigen‐specific antibody response might be considered short‐lived, moderately long‐lived, or very long‐lived, depending on the time frame in which the analysis is performed.