title: CD8 cell division maintaining cytotoxic memory occurs predominantly in the bone marrow.
abstract: Long-term persistence of Ag-experienced CD8 cells, a class of T lymphocytes with cytotoxic function, contributes to immunological memory against intracellular pathogens. After Ag clearance, memory CD8 cells are maintained over time by a slow proliferation, primarily cytokine driven. In this article, we show that the bone marrow (BM) is the crucial organ where such basal division of memory CD8 cells occurs. BM memory CD8 cells contain a higher percentage of proliferating cells than their corresponding cells in either spleen or lymph nodes from C57BL/6 mice. This occurs both in the case of memory-phenotype CD44(high) CD8 cells and in the case of Ag-specific memory CD8 cells. Importantly, the absolute number of Ag-specific memory CD8 cells dividing in the BM largely exceeds that in spleen, lymph nodes, liver, and lung taken together. In the BM, Ag-specific memory CD8 cells express lower levels of CD127, i.e., the alpha-chain of IL-7R, than in either spleen or lymph nodes. We interpret these results as indirect evidence that Ag-specific memory CD8 cells receive proliferative signals by IL-7 and/or IL-15 in the BM and propose that the BM acts as a saturable "niche" for the Ag-independent proliferation of memory CD8 cells. Taken together, our novel findings indicate that the BM plays a relevant role in the maintenance of cytotoxic T cell memory, in addition to its previously described involvement in long-term Ab responses.
authors.affiliation: Institute of Genetics and Biophysics, Adriano Buzzati Traverso, Consiglio Nazionale delle Ricerche, Naples, Italy.
authors.forename: Elisabetta
authors.initials: E
authors.lastname: Parretta
authors.forename: Giuliana
authors.initials: G
authors.lastname: Cassese
authors.forename: Pasquale
authors.initials: P
authors.lastname: Barba
authors.forename: Angela
authors.initials: A
authors.lastname: Santoni
authors.forename: John
authors.initials: J
authors.lastname: Guardiola
authors.forename: Francesca
authors.initials: F
authors.lastname: Di Rosa
mesh_terms: D019264:Adoptive Transfer; D000818:Animals; D001854:Bone Marrow Cells / Q000166:cytology* / Q000276:immunology* / Q000378:metabolism; D018414:CD8-Positive T-Lymphocytes / Q000166:cytology* / Q000276:immunology* / Q000378:metabolism; D002455:Cell Division / Q000235:genetics / Q000276:immunology*; D049109:Cell Proliferation; D002470:Cell Survival / Q000235:genetics / Q000276:immunology; D003601:Cytotoxicity Tests, Immunologic / Q000379:methods; D018984:Epitopes, T-Lymphocyte / Q000276:immunology; D005260:Female; D018960:Hyaluronan Receptors / Q000096:biosynthesis; D007156:Immunologic Memory / Q000235:genetics; D008099:Liver / Q000166:cytology / Q000276:immunology / Q000378:metabolism; D008168:Lung / Q000166:cytology / Q000276:immunology / Q000378:metabolism; D008198:Lymph Nodes / Q000166:cytology / Q000276:immunology / Q000637:transplantation; D018655:Lymphocyte Count; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D020395:Receptors, Interleukin-7 / Q000096:biosynthesis; D013154:Spleen / Q000166:cytology / Q000276:immunology / Q000378:metabolism
chemical_list: D018984:Epitopes, T-Lymphocyte; D018960:Hyaluronan Receptors; D020395:Receptors, Interleukin-7