Figure 2.

Protective mechanisms of antibody-mediated memory during reinfection

In an infection primarily controlled by Abs, protective immunity depends on the quantity and quality of available Abs, MBCs, and mTfh cells. The presence of sufficiently high amounts of neutralizing Abs will result in sterilizing immunity, negating the requirement for a recall response. If the production of neutralizing Abs is insufficient or has waned and is thus exceeded by the pathogen load, an infection will occur. The remaining neutralizing Abs will still limit the extent of infection, and both neutralizing and non-neutralizing Abs will facilitate the initiation of secondary immune responses by increasing the visibility of the pathogen to the IS (opsonization). If circulating Abs have dropped below effective levels, the initial pathogen entry can occur largely unchecked, resulting in an infection of increased speed and magnitude before MBCs and mTfh cells can provide protection via a recall response. In some cases, Ab memory may completely dissipate, resulting in susceptibility to full-blown infection and the requirement for a primary immune response.

Ab, antibody; PB, plasmablast; MBC, memory B cell; GC, germinal center; mTfh, follicular helper memory T cell.