Mechanisms that determine plasma cell lifespan and the duration of humoral immunity

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Abstract
Humoral immunity following vaccination or infection is mainly derived from two types of cells: memory B cells and plasma cells. Memory B cells do not actively secrete antibody but instead maintain their immunoglobulin in the membrane-bound form that serves as the antigen-specific B-cell receptor. In contrast, plasma cells are terminally differentiated cells that no longer express surface-bound immunoglobulin but continuously secrete antibody without requiring further antigenic stimulation. Pre-existing serum or mucosal antibody elicited by plasma cells (or other intermediate antibody-secreting cells) represents the first line of defense against reinfection and is critical for protection against many microbial diseases. However, the mechanisms involved with maintaining long-term antibody production are not fully understood. Here, we examine several models of long-term humoral immunity and present a new model, described as the 'Imprinted Lifespan' model of plasma cell longevity. The foundation of this model is that plasma cells are imprinted with a predetermined lifespan based on the magnitude of B-cell signaling that occurs during the induction of an antigen-specific humoral immune response. This represents a testable hypothesis and may explain why some antigen-specific antibody responses fade over time whereas others are maintained essentially for life.