Inhibition of Natural Killer Cell Function

人类自然杀伤（NK）细胞的活性受HLA i类杀伤细胞igg样受体（KIR）家族的调控。KIR和HLA基因型的组合与疾病易感性相关，包括对病毒感染的敏感性和妊娠障碍。我们研究的目的是确定与HLA-C结合的肽在多大程度上影响抑制性KIR与C1组或C2组HLA-C同种异体的特异性结合。内源性HLA-C*05:01相关肽被鉴定并检测了KIR与装载肽的HLA-C*05:01 （C2）和HLA-C*08:02 （C1）的结合，这两种肽分别是KIR2DL1和KIR2DL3的典型配体，尽管只有两个氨基酸差异。KIR2DL1与C2异型的特异性结合在大多数测试的肽中发生。相比之下，KIR2DL3与C1等位型的结合仅限于肽的一个子集，这就解释了为什么KIR2DL3C1的相互作用似乎比KIR2DL1C2弱。此外，KIR2DL3与C2异型的交叉反应性和功能性结合受到更大的限制，仅发生在少数肽上。此外，我们发现了两种肽，出乎意料地促进了C2同种异体特异性KIR2DL1与C1同种异体的结合。我们的数据显示，KIR在多种多肽的情况下与HLA-C结合是HLA-C异体型C2的强特异性特征，而多肽的更大选择性与HLA-C异体型更允许的反应性相关。肽序列驱动的KIR结合可能导致KIR基因型与特定HLA等位基因的疾病关联，并被病原体利用来调节NK细胞反应。

Human natural killer (NK) cell activity is regulated by a family of killer-cell Ig-like receptors (KIR) for HLA class I. Combinations of KIR and HLA genotypes are associated with disease susceptibility, including sensitivity to virus infection and disorders of pregnancy. The goal of our study was to determine the extent to which peptides bound to HLA-C influence the specific binding of inhibitory KIR to group C1 or C2 HLA-C allotypes. Endogenous HLA-C*05:01-associated peptides were identified and tested for KIR binding to peptide-loaded HLA-C*05:01 (C2) and HLA-C*08:02 (C1), which are canonical ligands for KIR2DL1 and KIR2DL3, respectively, despite having only two amino acid differences. Specific binding of KIR2DL1 to the C2 allotype occurred with most peptides tested. In contrast, KIR2DL3 binding to the C1 allotype was restricted to a subset of peptides, providing an explanation for why KIR2DL3C1 interactions appear to be weaker than KIR2DL1C2. Furthermore, cross-reactive and functional binding of KIR2DL3 with the C2 allotype was even more restricted, occurring with only a few peptides. Moreover, we identified two peptides that, unexpectedly, promoted binding of the C2 allotype-specific KIR2DL1 to the C1 allotype. Our data show that KIR binding to HLA-C in the context of multiple peptides is a feature of strong specificity for HLA-C allotype C2, whereas greater selectivity for peptides is associated with more permissive reactivity with HLA-C allotypes. Peptide sequence-driven binding of KIR could lead to disease associations of KIR genotypes with specific HLA alleles, and be exploited by pathogens to modulate NK cell responses. The inhibitory function of killer cell immunoglobulin-like receptors (KIR) that bind HLA-C and block activation of human natural killer (NK) cells is dependent on zinc. We have reported that zinc induced the assembly of soluble KIR into filamentous polymers, as detected by electron microscopy, which depolymerized after zinc chelation. Similar KIR filaments were isolated from lysates of cells treated with zinc, and membrane protrusions enriched in zinc were detected on whole cells by scanning electron microscopy and imaging mass spectrometry. Two independent mutations in the extracellular domain of KIR, away from the HLA-C binding site, impaired zinc-driven polymerization and inhibitory function. KIR filaments formed spontaneously, without addition of zinc, at functional inhibitory immunological synapses of NK cells with HLA-C+ cells. Adding to the recent paradigm of signal transduction through higher-order molecular assemblies, zinc-induced polymerization of inhibitory KIR represents an unusual mode of signaling by a receptor at the cell surface. IL-15 is essential for NK cell survival, proliferation, and activation. Stimulation by IL-15 occurs through trans-presentation of IL-15, which is bound to the IL-15 receptor chain (IL-15R) expressed on other cells, to the IL-2 receptor and c chains expressed by NK cells. As IL-15 transpresentation occurs in the context of cell-to-cell contacts, we tested if IL-15 transpresentation to human NK cells was sensitive to co-engagement of inhibitory receptors. We found that NK cell proliferation induced by IL-15 transpresentation was negatively regulated by co-engagement of either NKG2A or KIR inhibitory receptors. This negative regulation occurred selectively in the PI3KAktmTORC1S6 kinase pathway, as phosphorylation of Akt and ribosomal protein S6 were reduced upon co-engagement of inhibitory receptor, while phosphorylation of Stat5 and NK cell survival were not inhibited. These results reveal a novel mechanism to attenuate IL-15 dependent NK cell proliferation and suggest that inhibitory NK cell receptors contribute to NK cell homeostasis.