NOVEL CD32 ISOFORMS MODULATE NK CELL FUNCTIONS

人类自然杀伤(NK)细胞能够自发地杀死某些肿瘤和病毒感染的细胞。此外，NK细胞还可以通过抗体依赖的细胞毒作用(ADCC)杀伤被抗体包裹的靶细胞，正是其与NK细胞表面的Fc受体(FcGammaR)结合的Ig G的Fc部分为裂解机制的激活提供信号。几乎所有的NK细胞都表达FcGammaRIII，该受体参与了NK细胞介导的ADCC。直到最近，这还被认为是唯一在NK细胞上表达的FcGammaR。然而，我们最近发现，来自某些个体的NK细胞也表达高水平的FcGammaRII，并发现这些是FcGammaRIIC基因的产物，FcGammaRIIC基因是一种在任何细胞中都没有很好特征的亚型。我们进一步证明，在第一细胞外(EC1)区域的AA 13的等位基因多态导致NK细胞是CD32neg或CD32pos的个体。当该分子在NK细胞上表达时，可触发ADCC并增加细胞内的钙离子流量。此外，利用两种FcGammaRIIc亚型转染Jurkat细胞，我们确定了这两种FcGammaRIIc亚型的配体结合特异性和信号转导途径。这些研究具有潜在的意义，因为以前没有发现NK细胞表达CD32，因此这可能代表了一种激活和/或调节NK细胞裂解的新手段。基于这些数据，我们推测，某些个体NK细胞上存在高水平的FcGammaRII表达，通过激活和/或调节NK细胞的裂解和免疫调节功能来影响其NK细胞的功能。本研究旨在确定人类NK细胞表达的新的CD32亚型的功能意义，并通过评估它们在NK细胞功能中的作用来验证我们的假设。该提案的具体目的是：1)确定新的CD32亚型在正常NK细胞中的功能意义；2.确定MHC I类特异性抑制受体在CD32介导的功能调节中的作用；3)评估NK细胞对CD32pos或CD32neg个体肿瘤靶点的ADCC活性的可能差异。

Human natural killer (NK) cells are capable of spontaneously killing certain tumor and virus-infected cells. In addition, NK cells can kill IgG antibody-coated target cells via antibody- dependent cellular cytotoxicity (ADCC) and it is the Fc portion of the IgG binding to an Fc receptor (FcgammaR) on the surface of the NK cell that provides the signal for the activation of the lytic machinery. Almost all NK cells express FcgammaRIII, and this receptor has been shown to be involved in NK cell-mediated ADCC. Until recently this was thought to be the only FcgammaR expressed on NK cells. However, we have recently shown that NK cells, from certain individuals, also express high levels of FcgammaRII, and found these to be products of the FcgammaRIIC gene, an isoform that has not been well characterized in any cell. We have further shown that an allelic polymorphism of aa 13 in the first extracellular (EC1) domain results in individuals whose NK cells are CD32neg or CD32pos. This molecule, when expressed on NK cells, can trigger ADCC and increases in intracellular CA+2 flux. In addition, using Jurkat cells transfected with two FcgammaRIIc isoforms we have defined the ligand binding specificity and signal transduction pathway of these FcgammaRs. These studies are of potential significance because NK cells have not been previously shown to express CD32 and thus this potentially represents a new means of activating and/or regulating NK cell lysis. Based on these data we hypothesize that the presence of high levels of FcgammaRII expression on NK cells of some individuals influences the function of their NK cells by activating and/or regulating the lytic and immunoregulatory function of NK cells. The present proposal is aimed at determining the functional significance of the novel CD32 isoforms expressed by human NK cells and to test our hypothesis, by assessing their role in NK cell functions. The specific aims of the proposal are: 1) To determine the functional significance of novel CD32 isoforms in normal NK cells; 2. To determine the role of MHC class I-specific inhibitory receptors in the modulation of functions mediated by CD32; 3) To assess the possible differences in ADCC activity of NK cells against tumor targets from CD32pos or CD32neg individuals.