title: Distinct mechanisms control human naive and antigen-experienced CD8+ T lymphocyte proliferation.
abstract: Human Ag-specific CD8(+) T lymphocytes are heterogeneous and include functionally distinct populations. In this study, we report that at least two distinct mechanisms control the expansion of circulating naive, memory, and effector CD8(+) T lymphocytes when exposed to mitogen or Ag stimulation. The first one leads to apoptosis and occurs shortly after in vitro stimulation. Susceptibility to cell death is prominent among primed T cell subsets, and it is inversely correlated with the size of the ex vivo Bcl-2(high) population within these subsets. Importantly, the Bcl-2(high) phenotype is associated to the proportion of responsive CD8(+) T cells, independently of their differentiation stage. The second one depends on the expression of newly synthesized cyclin-dependent kinase inhibitor p16(INK4a) that occurs in a significant fraction of T cells that had been actively cycling, leading to their cell cycle arrest upon stimulation. Strikingly, accumulation of p16(INK4a) protein preferentially occurs in naive as opposed to primed derived T lymphocytes and is not related to apoptosis. Significant levels of p16 are readily detectable in a small number of ex vivo CD8(+) T cells. Our observations reveal that activation-induced p16 expression represents an alternative process to apoptosis, limiting the proliferation potential of activated naive derived T lymphocytes.
authors.affiliation: Swiss Institute for Experimental Cancer Research, Epalinges, Switzerland.
authors.forename: Marco
authors.initials: M
authors.lastname: Migliaccio
authors.forename: Pedro Miguel Sousa
authors.initials: PM
authors.lastname: Alves
authors.forename: Pedro
authors.initials: P
authors.lastname: Romero
authors.forename: Nathalie
authors.initials: N
authors.lastname: Rufer
mesh_terms: D000328:Adult; D000941:Antigens / Q000276:immunology*; D018414:CD8-Positive T-Lymphocytes / Q000166:cytology* / Q000276:immunology*; D002454:Cell Differentiation; D049109:Cell Proliferation; D002478:Cells, Cultured; D006801:Humans; D007156:Immunologic Memory / Q000276:immunology*; D007700:Kinetics; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism
chemical_list: D000941:Antigens; D019253:Proto-Oncogene Proteins c-bcl-2