title: Antagonistic effect of NK cells on alternatively activated monocytes: a contribution of NK cells to CTL generation.
abstract: Natural killer (NK) cells fulfill essential accessory functions for the priming of antigen-specific cytotoxic T lymphocytes (CTLs). On the basis of a NKG2D-ligand-positive tumor model, we obtained results implicating NK-mediated regulatory as well as NK-mediated cytolytic activities in the initiation and persistence of CTL activity. Indeed, CD8(+) T-cell-dependent tumor rejection requires NK cell function in vivo, because tumors will progress both on depletion of NK cells or in the absence of optimal NK activity. Here we provide evidence that the absence of NK cells during subcutaneous tumor growth will abrogate generation of antitumor CTL responses and that this process can be linked to the expansion of alternatively activated monocytes. Indeed, our in vitro studies demonstrate that in splenic cultures from NK-deficient tumor-bearing mice, lack of type 1-associated cytokines correlates with the presence of type 2 (alternatively activated) monocytes and the production of type 2 cytokines. Furthermore, these type 2 monocyte-containing splenic adherent populations potently suppress subsequent memory CTL restimulation. We evaluated the role of NK lytic effector functions in the efficient switch of the immune system toward classical (type 1) activation by including differentially activated monocytic populations as targets in cytotoxicity assays. The results indicate that the accessory function of NK cells depends partially on the ability of activated NK cells to preferentially engage type 2 antigen-presenting cells. Thus, when the immune system tends to be type 2 oriented, NK cells can drive an efficient type 2 --> type 1 switch in the population of antigen-presenting cells to provide signaling for the generation of CTLs.
authors.affiliation: Department of Cellular Immunology, Flanders Interuniversity Institute for Biotechnology, Vrije Universiteit Brussel, St Genesius Rode, Belgium. abgeldho@vub.ac.be
authors.forename: Anja B
authors.initials: AB
authors.lastname: Geldhof
authors.forename: Jo A
authors.initials: JA
authors.lastname: Van Ginderachter
authors.forename: YuanQing
authors.initials: Y
authors.lastname: Liu
authors.forename: Wim
authors.initials: W
authors.lastname: Noël
authors.forename: Geert
authors.initials: G
authors.lastname: Raes
authors.forename: Patrick
authors.initials: P
authors.lastname: De Baetselier
mesh_terms: D000818:Animals; D000938:Antigen-Presenting Cells / Q000502:physiology; D002450:Cell Communication; D016207:Cytokines / Q000378:metabolism; D005260:Female; D007156:Immunologic Memory; D015979:Killer Cells, Lymphokine-Activated / Q000276:immunology; D007694:Killer Cells, Natural / Q000276:immunology*; D016399:Lymphoma, T-Cell / Q000276:immunology; D051379:Mice; D008815:Mice, Inbred Strains; D009000:Monocytes / Q000166:cytology / Q000276:immunology*; D013602:T-Lymphocytes, Cytotoxic / Q000166:cytology / Q000276:immunology*; D018418:Th2 Cells / Q000378:metabolism; D014407:Tumor Cells, Cultured
chemical_list: D016207:Cytokines