title: The nature of the lymphopenic environment dictates protective function of homeostatic-memory CD8+ T cells.
abstract: A functional memory T cell pool is critical for resistance to pathogen reinfection. Lymphopenia produces memory-like CD8(+) T cells through homeostatic proliferation, and such "HP-memory" cells can control lethal bacterial infections similarly to conventional, antigen-experienced, memory T cells. These 2 pathways for memory T cell generation are quite distinct. We show here, however, that similar factors are required for production of protective memory CD8 T cells via both homeostatic and conventional pathways. Induction of protective HP-memory CD8 T cells requires CD4(+) T cell "help," which we show is antigen nonspecific yet requires CD40L-CD40 interactions with host cells. The functional competence of HP-memory CD8 T cells also requires release of endogenous bacterial components (which follows irradiation-induced lymphopenia), potentially mimicking the role of adjuvants in conventional immune responses. Lymphopenic environments lacking these key factors support similar CD8 T cell homeostatic proliferation and the acquisition of memory phenotype, yet the HP-memory cells generated are defective in pathogen elimination. These findings suggest unexpected parallels in the requirements for generating protective memory CD8 T cells by distinct pathways, and they suggest ways to bolster immune competence during recovery from lymphopenia.
authors.affiliation: Department of Laboratory Medicine and Pathology, Center for Immunology, University of Minnesota Medical Center, Minneapolis, MN 55454, USA.
authors.forename: Sara E
authors.initials: SE
authors.lastname: Hamilton
authors.forename: Stephen C
authors.initials: SC
authors.lastname: Jameson
mesh_terms: D000818:Animals; D015496:CD4-Positive T-Lymphocytes / Q000276:immunology; D018414:CD8-Positive T-Lymphocytes / Q000276:immunology*; D005434:Flow Cytometry; D006706:Homeostasis; D007156:Immunologic Memory; D018664:Interleukin-12 / Q000494:pharmacology; D008231:Lymphopenia / Q000276:immunology*; D051379:Mice; D008810:Mice, Inbred C57BL
chemical_list: D018664:Interleukin-12