Jerome Werkmeister

The effect of unphosphorylated and phosphorylated sugar moieties on human and mouse natural killer cell activity: IS there selective inhibition at the level of target recognition and lytic acceptor site?

A number of different sugars were investigated for their effect on human and mouse natural killer cell (NK)-mediated cytolysis. From the pool of nonphosphorylated sugars, D-mannose, N-acetyl-D-glucosamine (NAcGlc), D-glucose, and, to a lesser extent, beta-gentiobiose were found to inhibit human NK cytolysis. Mouse NK activity against YAC-1 target cells was reduced consistently in the presence of D-mannose and NAcGlc only. The sugars, NAcGlc, D-glucose, and beta-gentiobiose, were specifically inhibitory against NK-mediated cytolysis with no inhibitory effects being observed against ADCC, monocyte-mediated cytolysis, or CTL activity. Pretreatment and washing at either the target or effector cell level as well as direct target binding assays using Percoll-purified NK cells indicated that at least NAcGlc and beta-gentiobiose function at the recognition stage of NK cytolysis. D-Mannose, which was the most effective nonphosphorylated sugar inhibitor, was capable of inhibiting all cell-mediated cytotoxic mechanisms tested (NK, ADCC, monocyte, and CTL) and its action did not appear to be solely due to an impairment in the recognition event. All the phosphorylated sugars caused significant inhibition of human and mouse NK-mediated cytolysis, although repeated analyses of sugar titration curves consistently showed mannose-6-phosphate (Man-6-P) to be the most effective inhibitor. Inhibition with the phosphorylated sugars was apparent against all cytotoxic mechanisms investigated. It is possible that these sugars may function as general metabolic inhibitors or may activate a common signal which negatively regulates cell-mediated cytotoxic mechanisms. Nevertheless, the relative degree of inhibition with the majority of these sugars (particularly Man-6-P) was greater against NK and ADCC activity than against monocyte and CTL activity. Furthermore, studies with selected well-characterized human and mouse NK-resistant target cells strongly indicated that these sugars, particularly Man-6-P, compete at an acceptor site responsible for the uptake of the NK lytic factor, which is independent of the recognition structure(s).

Tumor cell differentiation modulates susceptibility to natural killer cells

Abstract Induced differentiation in three human cell lines altered their sensitivity specifically to human natural killer (NK) cells by affecting their expression of NK target antigens. Differentiation of HL-60, a promyelocytic leukemia cell line, and the erythroleukemic cell line K562 was accompanied by a concomitant decrease in susceptibility to NK-mediated lysis whereas induction of MeWo melanoma cells resulted in an enhanced sensitivity to lysis. Our findings suggest that target cell susceptibility to NK-mediated lysis may in part be dependent on the stage of differentiation of the tumor cell target.

SPECIFICITY OF NATURAL KILLER (NK) CELLS: NATURE OF TARGET CELL STRUCTURES

Publisher Summary This chapter discusses the specificity of natural killer cells and nature of target cell structures. NK cells have now demonstrated the killing of a wide variety of malignant cells and some normal cells to a lesser extent without any apparent need for prior stimulation. Studies using unlabelled targets in cross competition assays with a panel of Cr labeled target cells have shown that cytotoxicity could be inhibited by some but not all target cells. Those cells most sensitive to NK lysis proved to be the best competitors, and a good correlation was found between susceptibility to direct lysis and competition among a variety of targets. The ability of different cell lines to compete inferred but did not prove the existence of cross reacting target antigens and a complementary receptor on the effector cell. The studies on human target cell lines have demonstrated the presence of neutral 140,000 d glycoproteins which inhibited NK but not antibody-dependent cellular cytotoxicity. Similar structures were not found in supernatants of NK-resistant cell lines. The results from both murine and human systems demonstrate that glycoproteins are effective in inhibiting target cell–effector cell interactions and subsequent cytolysis, suggesting carbohydrate moieties as possible target structures.

THE ROLE OF FREE OXYGEN RADICALS IN THE ACTIVATION OF THE NK CYTOLYTIC PATHWAY1

Publisher Summary This chapter discusses the role of free oxygen radicals in the activation of the natural killer (NK) cytolytic pathway. The cytolytic pathway can be divided into four discrete stages, which include recognition and binding to the target and triggering and activation of the lytic mechanisms. An examination of low-NK responsiveness in humans has shown that individuals with this stable, selective defect have normal frequencies of HNK-1+ NK cells, which bind normally to the tumor targets and are boosted normally by interferon but fail to become activated as judged by a 60% decrease in the burst of oxygen radicals that are normally generated following target–effector interaction. The data suggest that the generation of oxygen radicals is an early event in the triggering and activation of the lytic mechanism, stage 2. The block in NK cytolysis appears to be in stage 3 because binding to the target is normal and is followed by normal triggering and production of oxygen radicals, thereby indicating that the oxygen radicals normally appear prior to the step in the cytolytic pathway, which is blocked in the Chediak–Higashi syndrome.