Costimulation of Multiple NK Cell Activation Receptors by NKG2D

Abstract

The activation of NK cells is mediated through specific interactions between activation receptors and their respective ligands. Little is known, however, about whether costimulation, which has been well characterized for T cell activation, occurs in NK cells. To study the function of NKG2D, a potential NK costimulatory receptor, we have generated two novel hamster mAbs that recognize mouse NKG2D. FACS analyses demonstrate that mouse NKG2D is expressed on all C57BL/6 IL-2-activated NK (lymphokine-activated killer (LAK)) cells, all splenic and liver NK cells, and ∼50% of splenic NKT cells. Consistent with limited polymorphism of NKG2D, its sequence is highly conserved, and the anti-NKG2D mAbs react with NK cells from a large number of different mouse strains. In chromium release assays, we show that stimulation of NK cells with anti-NKG2D mAb can redirect lysis. Also, enhanced lysis of transfected tumor targets expressing NKG2D ligand could be inhibited by addition of anti-NKG2D mAb. Interestingly, stimulation of LAK cells via NKG2D alone does not lead to cytokine release. However, stimulation of LAK via both an NK activation receptor (e.g., CD16, NK1.1, or Ly-49D) and NKG2D leads to augmentation of cytokine release compared with stimulation through the activation receptor alone. These results demonstrate that NKG2D has the ability to costimulate multiple NK activation receptors.

Continuous CD27 triggering in vivo strongly reduces NK cell numbers

“…Upon activation, they directly eliminate target cells through exocytosis of perforin-and granzyme-containing granules, or by Fas ligand (CD178) or TRAIL pathways [3][4][5][6][7]. NK cells also produce cytokines and chemokines, which enable them to recruit non-specific haematopoetic cells, activate dendritic cells and prime adaptive lymphocytes [8][9][10][11]. As such, NK cells bridge between innate and adaptive immunity.…”

Systemic NKG2D Down-Regulation Impairs NK and CD8 T Cell Responses In Vivo

“…In humans, NKG2D is present on most NK cells, CD8 T cells, and ␥␦ T cells in association with the adaptor protein DAP10 (1,2). In mice, CD8 T cells express NKG2D only upon activation, whereas NK cells, NKT cells, and some ␥␦ T cells constitutively express NKG2D (3,4). Different from humans, activated mouse NK cells generate a second NKG2D isoform with a shortened cytoplasmic domain (NKG2D-S), which is capable of pairing with both DAP10 and DAP12, whereas the constitutively expressed NKG2D-L isoform exclusively associates with DAP10 (5,6).…”

“…Whereas the ectodomain of NKG2D is fairly conserved in mouse and man, the various MHC class I-related binding partners of NKG2D are highly diverged. In humans, the MHC-encoded MIC molecules MHC class I chain-related proteins A and B (MICA and MICB) 3 and five members of the UL16-binding protein (ULBP) family (ULBP1-4; RAET1G) ligate NKG2D and consequently trigger NK cells (13)(14)(15). In vitro, cell stress-inducible MIC molecules are expressed by many tumor cell lines and up-regulated upon infection with human CMV, Mycobacterium tuberculosis, and Escherichia coli (12,16).…”

Two Human ULBP/RAET1 Molecules with Transmembrane Regions Are Ligands for NKG2D

“…NKG2D is not limited to NK cells and is also expressed on activated CD8 ϩ T cells, ␥␦ T cells, and activated macrophages (14). A remarkable property of NKG2D is that it can be either directly stimulatory or costimulatory (15,16) based on its association with either the DAP10 or DAP12 signaling adapter molecules, respectively (17,18).…”