β2 -Microglobulin-deficient NK cells show increased sensitivity to MHC class I-mediated inhibition, but self tolerance does not depend upon target cell expression of H-2Kb and Db heavy chains

Abstract

Mice lacking g 2-microglobulin (g 2 m − mice) express greatly reduced levels of MHC class I molecules, and cells from g 2 m − mice are therefore highly sensitive to NK cells. However, NK cells from g 2 m − mice fail to kill g 2 m − normal cells, showing that they are self tolerant. In a first attempt to understand better the basis of this tolerance, we have analyzed more extensively the target cell specificity of g 2 m − NK cells. In a comparison between several MHC class I-deficient and positive target cell pairs for sensitivity to g 2 m − NK cells, we made the following observations: First, g 2 m − NK cells displayed a close to normal ability to kill a panel of MHC class I-deficient tumor cells, despite their nonresponsiveness to g 2 m − concanavalin A (Con A)-activated T cell blasts. Secondly, g 2 m − NK cells were highly sensitive to MHC class I-mediated inhibition, in fact more so than g 2 m + NK cells. Thirdly g 2 m − NK cells were not only tolerant to g 2 m − Con A blasts but also to Con A blasts from H-2K b− /D b− double deficient mice in vitro. We conclude that NK cell tolerance against MHC class I-deficient targets is restricted to nontransformed cells and independent of target cell expression of MHC class I free heavy chains. The enhanced ability of g 2 m − NK cells to distinguish between MHC class I-negative and-positive target cells may be explained by increased expression of Ly49 receptors, as described previously. However, the mechanisms for enhanced inhibition by MHC class I molecules appear to be unrelated to self tolerance in g 2 m − mice, which may instead operate through mechanisms involving triggering pathways. Abbreviations: I 2 m: g 2-Microglobulin TAP: Transporter associated with antigen processing

The Murine Cytomegalovirus Immune Evasion Protein m4/gp34 Forms Biochemically Distinct Complexes with Class I MHC at the Cell Surface and in a Pre-Golgi Compartment

“…These pellets were dissociated, and the resulting Nonidet P-40 supernatants were subjected to secondary immunoprecipitation, as described above. Nonidet P-40-stable pellets are shown in lanes 1-10; immunoprecipitations from Nonidet P-40 supernatants are shown in lanes [11][12][13][14][15][16][17][18][19][20]. As seen previously in Fig.…”

“…Precipitates were resuspended in Nonidet P-40 lysis buffer to disrupt Nonidet P-40-unstable complexes, after which they were recentrifuged to precipitate the Nonidet P-40-stable complexes shown in lanes 1-10. Supernatant remaining from these immunoprecipitations was divided in half and subjected to sequential precipitation with two different Abs, as shown (lanes [11][12][13][14][15][16][17][18][19][20]. All samples in B and C were digested with Endo H. report, Fig.…”

Analysis of natural killer cells in TAP2-deficient patients: expression of functional triggering receptors and evidence for the existence of inhibitory receptor(s) that prevent lysis of normal autologous cells

“…15 Thus, our current data on TAP2 Ϫ/Ϫ NK cells are clearly reminiscent of previous data obtained in ␤2-microglobulin-deficient or TAP-1 knockout mice. 37,38 These studies showed that ␤2-m Ϫ NK cells, while sparing autologous concanavalin A blasts and bone marrow cells, could lyse allogeneic major histocompatibility complex class I Ϫ tumors. In view of our current finding that TAP2 Ϫ/Ϫ NK cells express functional NCR, it is unlikely that they fail to kill PHA blasts because of the lack of still undefined triggering receptor(s).…”

Retuning of Mouse NK Cells after Interference with MHC Class I Sensing Adjusts Self-Tolerance but Preserves Anticancer Response

“…3D). Importantly, B6 NK cells transferred to a b 2 m À/À environment, rejected MHC class I À leukemia cells equally well, and much better than na€ ve b 2 m À/À mice (35). Similar to NK cells subjected to inhibitory receptor blockade, NK cells could thus still distinguish between MHC class I-sufficient and -deficient malignant cells, despite a reduced rejection of MHC class I À healthy cells.…”