Mathematical models of memory T-cell compartment size and repertoire dynamics

Immunity to infections is conferred by the immune system via memory cells, which are created when a host first encounters a virus and serve as sentinels that activate quickly to eliminate any reinfections that occur. Some memory cells secrete antibodies against extracellular invaders, others act as coordinators of the immune response, and some-the memory CD8+ T-cells-eradicate intracellular pathogens by killing infected host cells. These latter cells are each equipped with T-cell receptors that recognize and become activated only in response to a particular virus; thus, a host must possess a broad repertoire of memory CD8+ T-cells with a range of specificities to effectively protect against viral invasions. The breadth of the memory repertoire is constrained, however, by the fact that the number of memory CD8+ T-cells is remarkably constant between infections. Therefore, some attrition of existing memory cells is necessary following infections to make room for new memory cells. Furthermore, some viruses induce memory attrition early in infections creating an underfilled memory compartment; cells must then proliferate to restore the memory compartment to its homeostatic size.