Minimal requirement for induction of natural cytotoxicity and intersection of activation signals by inhibitory receptors

Blood. 2009 Sep 24;114(13):2657-66. doi: 10.1182/blood-2009-01-201632. Epub 2009 Jul 23.


Natural killer (NK) cells provide innate control of infected and neoplastic cells. Multiple receptors have been implicated in natural cytotoxicity, but their individual contribution remains unclear. Here, we studied the activation of primary, resting human NK cells by Drosophila cells expressing ligands for receptors NKG2D, DNAM-1, 2B4, CD2, and LFA-1. Each receptor was capable of inducing inside-out signals for LFA-1, promoting adhesion, but none induced degranulation. Rather, release of cytolytic granules required synergistic activation through coengagement of receptors, shown here for NKG2D and 2B4. Although engagement of NKG2D and 2B4 was not sufficient for strong target cell lysis, collective engagement of LFA-1, NKG2D, and 2B4 defined a minimal requirement for natural cytotoxicity. Remarkably, inside-out signaling induced by each one of these receptors, including LFA-1, was inhibited by receptor CD94/NKG2A binding to HLA-E. Strong inside-out signals induced by the combination of NKG2D and 2B4 or by CD16 could overcome CD94/NKG2A inhibition. In contrast, degranulation induced by these receptors was still subject to inhibition by CD94/NKG2A. These results reveal multiple layers in the activation pathway for natural cytotoxicity and that steps as distinct as inside-out signaling to LFA-1 and signals for granule release are sensitive to inhibition by CD94/NKG2A.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, N.I.H., Intramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Antigens, CD / metabolism
  • Antigens, CD / physiology
  • Cell Degranulation / immunology
  • Cells, Cultured
  • Cytotoxicity, Immunologic / immunology*
  • Drosophila
  • Humans
  • K562 Cells
  • Killer Cells, Natural / immunology
  • Killer Cells, Natural / metabolism
  • Killer Cells, Natural / physiology*
  • Lymphocyte Activation / immunology*
  • Lymphocyte Function-Associated Antigen-1 / metabolism
  • Lymphocyte Function-Associated Antigen-1 / physiology
  • NK Cell Lectin-Like Receptor Subfamily D / metabolism
  • NK Cell Lectin-Like Receptor Subfamily D / physiology
  • NK Cell Lectin-Like Receptor Subfamily K / metabolism
  • NK Cell Lectin-Like Receptor Subfamily K / physiology
  • Receptors, Immunologic / metabolism
  • Receptors, Immunologic / physiology
  • Receptors, Natural Cytotoxicity Triggering / metabolism
  • Receptors, Natural Cytotoxicity Triggering / physiology*
  • Signal Transduction / immunology
  • Signal Transduction / physiology
  • Signaling Lymphocytic Activation Molecule Family


  • Antigens, CD
  • Cd244a protein, mouse
  • KLRD1 protein, human
  • KLRK1 protein, human
  • Lymphocyte Function-Associated Antigen-1
  • NK Cell Lectin-Like Receptor Subfamily D
  • NK Cell Lectin-Like Receptor Subfamily K
  • Receptors, Immunologic
  • Receptors, Natural Cytotoxicity Triggering
  • Signaling Lymphocytic Activation Molecule Family