title: Fratricide: a mechanism for T memory-cell homeostasis.
abstract: Immunological memory depends on a self-renewing pool of antigen-specific T memory (Tm) cells but the homeostatic mechanisms that maintain the size and diversity of the pool are largely unknown. Competition for space or growth factors has been suggested as a mechanism but how these factors themselves are regulated is unclear. We suggest that Tm-cell fratricide by Fas-mediated apoptosis results in a density-dependent death rate that controls the size of the pool without requiring competition for resources or an external quorum-sensing mechanism. A mathematical model based on this concept predicts the known behaviour of the Tm pool, including observed differences in heterogeneity of the CD4 and CD8 compartments and might provide a paradigm for homeostasis of other haematopoietic-cell populations.
authors.affiliation: Immunobiology Unit, Institute of Child Health, University College London, 30 Guilford Street, WC1N 1EH, London, UK. rcallard@ich.ucl.ac.uk <rcallard@ich.ucl.ac.uk>
authors.forename: Robin E
authors.initials: RE
authors.lastname: Callard
authors.forename: Jaroslav
authors.initials: J
authors.lastname: Stark
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Yates
mesh_terms: D000818:Animals; D000941:Antigens / Q000008:administration & dosage; D017209:Apoptosis; D015496:CD4-Positive T-Lymphocytes / Q000166:cytology / Q000276:immunology; D018414:CD8-Positive T-Lymphocytes / Q000166:cytology / Q000276:immunology; D006706:Homeostasis; D006801:Humans; D007156:Immunologic Memory; D018448:Models, Immunological; D013601:T-Lymphocytes / Q000166:cytology / Q000276:immunology*
chemical_list: D000941:Antigens