Regulation Of Natural Killer Cell Activity

自然杀伤细胞（NK）是除B细胞和T细胞外的第三种淋巴细胞亚型。NK细胞在防御病毒和其他细胞内病原体方面具有重要的免疫功能。与B细胞和T细胞不同，NK细胞对抗原没有特异性，它们之所以得名，是因为它们可以在没有抗原事先刺激的情况下杀死细胞。NK细胞上识别主要组织相容性I类分子的抑制性受体阻止了正常健康细胞的杀伤。大量的受体激活NK细胞的细胞毒性反应已经被描述。然而，目前尚不清楚这些受体中的任何一种是否足以和/或必须激活天然细胞毒性。这个项目的主要目标是确定NK细胞活化的分子基础，并表征所涉及的受体。重建系统已开发测试的贡献，个别受体NK细胞毒性的活化。为了确定NK细胞激活的最低要求，在昆虫细胞系中表达了NK细胞受体的几种特异性配体。被激活的自然杀伤细胞（NK）在与敏感靶细胞接触时裂解肿瘤细胞和病毒感染细胞并产生干扰素- γ。这些效应反应在静止NK细胞中的调控尚不清楚。一种受体KIR2DL4被描述为具有诱导干扰素γ产生的独特特性，但不具有细胞毒性，在缺乏细胞因子的情况下静息NK细胞。相反，其他NK细胞活化受体诱导细胞毒性，但不产生干扰素。KIR2DL4对静止NK细胞产生ifn - γ的诱导作用被p38丝裂原活化蛋白激酶（MAPK）信号通路抑制剂阻断，而白细胞介素2诱导的干扰素- γ分泌对Erk MAPK通路的抑制敏感。这些结果揭示了静止NK细胞反应中的功能二分法（细胞因子产生与细胞毒性），这是由个体受体的信号决定的。gp49B受体对NK细胞和肥大细胞均有抑制作用。已经产生了gp49B基因缺失的小鼠。这种缺乏gp49的小鼠已经与一种基因型小鼠杂交了几代，以获得相当纯的遗传背景。NK细胞在gp49b缺陷小鼠体内发育正常，体外细胞毒活性正常。同样，肥大细胞在gp49b缺陷小鼠中正常发育，并在体外显示正常的脱颗粒活性。gp49B缺失小鼠的健康状态使得它们非常适合测试gp49B在感染期间控制免疫反应中的作用，特别是那些已知会引发NK或肥大细胞反应的小鼠。

Natural killer (NK) cells are a third subtype of lymphocytes besides B and T cells. NK cells provide an important immune function in the defense against viruses and other intracellular pathogens. Unlike B and T cells, NK cells do not exhibit specificity for antigen and they acquired their name because they can kill cells without prior stimulation by antigen. The killing of normal healthy cells is prevented by inhibitory receptors on NK cells that recognize major histocompatibility class I molecules. A large number of receptors that activate the cytotoxic response of NK cells have been described. However, it is not clear if any one of these receptors is sufficient and/or necessary to activate natural cytotoxicity. The major goal of this project is to define the molecular basis of NK cell activation and to characterize the receptors involved. A reconstitution system has been developed to test for the contribution of individual receptors to the activation of NK cell cytotoxicity. Several specific ligands of NK cell receptors have been expressed in an insect cell line in order to determine the minimal requirements for the activation of NK cells. Activated natural killer (NK) cells lyse tumor cells and virus-infected cells and produce interferon-gamma upon contact with sensitive target cells. The regulation of these effector responses in resting NK cells is not well understood. A receptor, KIR2DL4, was described that has the unique property of inducing interferon-gamma production, but not cytotoxicity, by resting NK cells in the absence of cytokines. In contrast, other NK cell activation receptors induced cytotoxicity but not interferon-gamma production. The induction by KIR2DL4 of IFN-gamma production by resting NK cells was blocked by an inhibitor of the p38 mitogen activated protein kinase (MAPK) signaling pathway, in contrast to the interleukin-2-induced interferon-gamma secretion that was sensitive to inhibition of the Erk MAPK pathway. These results reveal a functional dichotomy (cytokine production versus cytotoxicity) in the response of resting NK cells, as dictated by the signals of individual receptors. The gp49B receptor has an inhibitory activity in both NK cells and mast cells. Mice deficient in the gp49B gene have been generated. Such gp49-deficient mice have been crossed for several generations with a congenic strain of mice in order to obtain a fairly pure genetic background. NK cells developed normally in gp49B-deficient mice and displayed normal cytotoxic activity in vitro. Likewise, mast cells developed normally in gp49B-deficient mice and displayed normal degranulation activity in vitro. The healthy status of gp49B-null mice makes them very suitable for testing the role of gp49B in controlling immune responses during infections, in particular those known to elicit NK or mast cell responses.