Cell death and the maintenance of immunological memory

Immunological memory is found in diverse populations of a class of lymphocytes called T cells, that are held at roughly constant numbers. Its composition is in continuous flux as we encounter new pathogens and cells are lost. The mechanisms which preserve the memory T cell population in the face of these uncertain factors are largely unknown. We propose a mechanism for homeostasis, driven by density-dependent cell death, that both fits experimental data and naturally preserves the clonal composition of the T cell pool with fluctuating cell numbers. It also provides clues as to the source of differences in diversity between T cell memory subpopulations.