Dendritic Cell and Natural Killer Cell Interactions in H

天然杀伤（NK）细胞和树突状细胞（DC）在先天免疫应答期间的相互作用被认为极大地影响随后的抗原特异性适应性免疫应答的质量和强度。NK细胞-DC（NK-DC）串扰发生的机制包括细胞活化和成熟的相互增强以及NK细胞介导的未成熟DC（iDC）的消除。未成熟的iDC和抗原之间的第一次接触发生在炎症部位的外周组织中，其中iDC由驻留DC和其他细胞类型产生的细胞因子和趋化因子信号驱动从血流中募集。在抗原摄取后，iDC经历成熟过程，其允许所得成熟DC（mDC）迁移至次级淋巴组织，在那里它们引发抗原特异性T细胞应答。已经发现NK细胞在优化mDC的分化以引发有效的抗原特异性适应性免疫应答中极其重要。该过程需要NK-DC相互作用和NK细胞分泌特异性细胞因子。 在生理条件下，DC成熟程序直接由微生物信号以及由活化的NK细胞执行调节作用诱导。我们在这里表明，分泌IFN-γ，一个有效的诱导DC分化，？？当NK细胞暴露于由病毒血症而非病毒血症的HIV-1感染个体产生的自体mDC时，此外，最近证明促进DC成熟的能力基本上限于表达KIRneg/NKG 2Adull/NKp 30 pos表型的NK细胞。我们报道了来自HIV-1病毒血症个体的新鲜纯化的NK细胞表达增加的KIR水平，而NKG 2A和NKp 30的表达极低或不存在，特别是在CD 56阴性NK细胞中，这是一个在HIV-1病毒血症患者和健康供体中以非常低的频率存在的亚群。考虑到这些缺陷与病毒血症状态的相关性，我们的数据表明HIV-1直接或间接地干扰了DC的成熟过程。事实上，尽管与成熟表型相关的细胞表面标志物的表达，我们发现，来自病毒血症患者的mDC表现出几个功能缺陷，可能会损害mDC介导的NK细胞活化。在这些功能障碍的活动中，我们发现从病毒血症HIV-1感染受试者产生的自体mDC明显表现出诱导NK细胞增殖和NK细胞分泌IFN-g？的能力明显受损。IL-12是NK细胞活化和增殖的重要细胞因子。因此，如本研究所示，由病毒血症的HIV-1感染个体产生的mDC产生的IL-12的减少可能部分地解释了它们对NK细胞的缺陷性引发。 DC-NK细胞串扰的早期步骤中的损伤导致在组织感染部位或次级淋巴器官中限制HIV-1传播的能力的缺陷。mDC分泌的IL-10（在大多数系统中的HIV-1抑制性细胞因子）较低以及来自HIV-1感染的病毒血症患者的NK细胞的细胞溶解活性降低可能损害外周组织中HIV-1复制的抑制。此外，已经显示IL-10抑制DC共刺激分子的表达，并且因此，由病毒血症HIV-1感染个体产生的mDC的IL-10的弱产生可能部分地促成显著功能失调的mDC的成熟表型。 NK细胞被认为通过其影响响应于抗原摄取而经历成熟的DC的质量的独特且可能更重要的机制是通过杀死未能完成其成熟程序的iDC。最近的一项研究表明，从病毒血症的HIV-1感染患者产生的DC可以逃避自体NK细胞的裂解，但这种逃避的根本原因尚未确定。在本研究中，我们描述了导致NK细胞介导的自体iDC裂解受损的细胞机制，并表明这种现象仅限于那些持续高病毒血症的HIV-1感染个体。我们的数据表明，NKp 30和TRAIL的表达/分泌和功能显著受损，这在很大程度上解释了由病毒血症HIV-1感染受试者产生的自体iDC的高度缺陷的NK细胞介导的裂解。此外，我们表明，在该研究组中，表达不寻常的KIRpos/NKG 2Aneg/NKp 30 neg/TRAIL neg表型的CD 56 neg NK细胞的高度扩增，在病毒血症的HIV-1感染患者或健康供体中以非常低的频率存在的子集，可能解释了NK细胞对自体iDC的这种缺陷消除仅限于HIV-1阳性病毒血症患者的原因。 这种NK-DC串扰代表了所提出的先天免疫能够在次级淋巴器官中引发有效的适应性免疫应答的机制。与HIV-1病毒血症患者和未感染的对照受试者相比，慢性HIV-1感染病毒血症个体中高度缺陷的双向NK-DC串扰可能在HIV-1发病机制的背景下导致病毒从协调的先天性和适应性免疫应答中逃逸。

The interaction between natural killer (NK) cells and dendritic cells (DCs) during the innate immune response is thought to greatly impact the quality and strength of the subsequent antigen-specific adaptive immune response. Mechanisms whereby NK cell-DC (NK-DC) crosstalk occurs include reciprocal enhancement of cellular activation and maturation as well as NK cell-mediated elimination of immature DCs (iDCs). The first contact between immature iDCs and antigens occurs in peripheral tissue at sites of inflammation where iDCs are recruited from the bloodstream, driven by cytokine and chemokine signals produced by resident DCs and other cell types. After antigen uptake, iDCs undergo a maturation process that allows the resulting mature DCs (mDCs) to migrate to secondary lymphoid tissues where they prime an antigen-specific T cell response. NK cells have been found to be extremely important in optimizing the differentiation of mDCs in order to prime an effective antigen-specific adaptive immune response. This process requires both NK-DC interactions and NK cell secretion of specific cytokines. Under physiological conditions, the DC maturation program is induced directly by microbial signals as well as by activated NK cells performing a regulatory role. We show here that secretion of IFN-g, a potent inducer of DC differentiation, ??is significantly impaired when NK cells are exposed to autologous mDCs generated from viremic, but not aviremic, HIV-1 infected individuals. Moreover, it was recently demonstrated that the ability to promote DC maturation was essentially confined to NK cells expressing a KIRneg/NKG2Adull/NKp30pos phenotype. We reported that freshly purified NK cells from HIV-1 viremic individuals expressed increased levels of KIRs, while expression of NKG2A and NKp30 was extremely low or absent, particularly among the CD56neg NK cells, a subset present at very low frequencies in both aviremic HIV-1 infected patients and healthy donors. Given the association of these defects with the viremic state, our data suggest that HIV-1, directly or indirectly, interferes with the maturation process of DCs. In fact, despite the expression of cell surface markers associated with a mature phenotype, we found that mDCs derived from viremic patients exhibited several functional defects that could potentially impair the mDC-mediated activation of NK cells. Among these dysfunctional activities, we found that autologous mDCs generated from viremic HIV-1 infected subjects clearly exhibited a markedly impaired capacity to induce both NK cell proliferation and NK cell secretion of IFN-g?. IL-12 is an important cytokine for the activation and proliferation of NK cells. Thus, the reduced IL-12 production by mDCs generated from viremic HIV-1 infected individuals, as demonstrated in this study, may partially account for their defective priming of NK cells. Impairments in the early steps of DC-NK cell crosstalk result in a defect in the ability to limit HIV-1 spread at sites of tissue infection or in secondary lymphoid organs. The lower secretion of IL-10, an HIV-1 inhibitory cytokine in most systems, by mDCs as well as the reduced cytolytic activity of NK cells from HIV-1 infected viremic patients may impair inhibition of HIV-1 replication in the peripheral tissues. Furthermore, it has been shown that IL-10 inhibits the expression of DC co-stimulatory molecules, and, therefore, the weak production of IL-10 by mDCs generated from viremic HIV-1 infected individuals might in part contribute to the mature phenotype of the markedly dysfunctional mDCs. A unique and perhaps more important mechanism through which NK cells are thought to impact the quality of the DCs undergoing maturation in response to antigen uptake is by killing iDCs that failed their maturation program. A recent study showed that DCs generated from viremic HIV-1 infected patients can escape lysis by autologous NK cells, but the underlying cause(s) of this escape have not been identified. In the present study, we delineate the cellular mechanisms that account for impaired NK cell-mediated lysis of autologous iDCs and show that this phenomenon is restricted to those HIV-1-infected individuals with persistent high viremia. Our data demonstrate that the markedly impaired expression/secretion and function of NKp30 and TRAIL largely account for the highly defective NK cell mediated lysis of autologous iDCs generated from viremic HIV-1 infected subjects. Moreover, we show that, within this study group, the high expansion of CD56neg NK cells expressing the unusual KIRpos/NKG2Aneg/NKp30neg/TRAILneg phenotype, a subset present at very low frequencies in either aviremic HIV-1 infected patients or healthy donors, likely explains why this defective elimination of autologous iDCs by NK cells is confined to HIV-1 positive viremic patients. This NK-DC crosstalk represents the proposed mechanism by which the innate immunity is able to prime an effective adaptive immune response in secondary lymphoid organs. The highly defective bidirectional NK-DC crosstalk in chronically HIV-1-infected viremic individuals compared with HIV-1 aviremic patients and uninfected control subjects likely contributes, in the context of HIV-1 pathogenesis, to the escape of virus from a coordinated innate and adaptive immune response.