Micropolymorphisms within human leukocyte antigen (HLA) class I molecules can change the architecture of the peptide-binding cleft, leading to differences in peptide presentation and T cell recognition. The impact of such HLA variation on natural killer (NK) cell recognition remains unclear. Given the differential association of HLA-B*57:01 and HLA-B*57:03 with the control of HIV, recognition of these HLA-B57 allomorphs by the killer cell immunoglobulin-like receptor (KIR) 3DL1 was compared. Despite differing by only two polymorphic residues, both buried within the peptide-binding cleft, HLA-B*57:01 more potently inhibited NK cell activation. Direct-binding studies showed KIR3DL1 to preferentially recognize HLA-B*57:01, particularly when presenting peptides with positively charged position (P)Ω-2 residues. In HLA-B*57:01, charged PΩ-2 residues were oriented toward the peptide-binding cleft and away from KIR3DL1. In HLA-B*57:03, the charged PΩ-2 residues protruded out from the cleft and directly impacted KIR3DL1 engagement. Accordingly, KIR3DL1 recognition of HLA class I ligands is modulated by both the peptide sequence and conformation, as determined by the HLA polymorphic framework, providing a rationale for understanding differences in clinical associations.

Natural killer (NK) cells play important roles in immune surveillance. However, the tumor microenvironment suppresses NK cell function and allows cancer cells to evade immune detection. In this study, we investigated whether the thyroid cancer cell microenvironment has this effect on NK cells. We found that prostaglandin (PG) E2 produced by thyroid cancer cells suppressed the cytolytic activity of NK cells by inhibiting the expression of the natural cytotoxicity receptors NKp44 and NKp30 and the death receptor tumor necrosis factor-related apoptosis-inducing ligand. PGE2 and cyclooxygenase-2 were highly expressed in thyroid cancer cells; moreover, anaplastic thyroid cancer cells released higher amounts of PGE2 than the papillary subtype, which was associated with suppression of NK cell-inducing nuclear factor-κB and mitogen-activated protein kinase/extracellular signal-regulated kinase pathways via PGE2 receptor (EP) 2 and EP4 expressed on the NK cell surface. In addition, PGE2 inhibited the functional maturation of NK cells and reduced their cytotoxicity against target cells. These results indicate that PGE2 promotes thyroid cancer progression by inhibiting NK cell maturation and cytotoxicity. Thus, therapeutic strategies that target PGE2 in thyroid cancer could potentiate the immune response and improve patient prognosis.

Based on previous findings supporting HLA-F as a ligand for KIR3DL2 and KIR2DS4, we investigated the potential for MHC-I open conformers (OCs) as ligands for KIR3DS1 and KIR3DL1 through interactions measured by surface plasmon resonance. These measurements showed physical binding of KIR3DS1 but not KIR3DL1 with HLA-F and other MHC-I OC while also confirming the allotype specific binding of KIR3DL1 with MHC-I peptide complex. Concordant results were obtained with biochemical pull-down from cell lines and biochemical heterodimerization experiments with recombinant proteins. In addition, surface binding of HLA-F and KIR3DS1 to native and activated NK and T cells was coincident with specific expression of the putative ligand or receptor. A functional response of KIR3DS1 was indicated by increased granule exocytosis in activated cells incubated with HLA-F bound to surfaces. The data extend a model for interaction between MHC-I open conformers and activating KIR receptors expressed during an inflammatory response, potentially contributing to communication between the innate and adaptive immune response.

Natural killer (NK) cells have been demonstrated to inhibit tumor growth. However, the role of NK cells in the inhibition of hepatocellular carcinoma metastasis is not well understood. The present study aimed to investigate the roles that NK cells may serve in inhibiting hepatocellular carcinoma metastasis. The role of isolated NK cells in the inhibition, proliferation, migration and invasion of the hepatoma cell line, MHCC97-H, was examined in vitro. Additionally, the survival rate of NK cells labeled with carboxyfluorescein diacetate-succinimidyl ester was assessed in vivo. An orthotopic implantation model was used to evaluate the role of NK cells in suppressing MHCC97-H cells in vivo. The effect of interleukin (IL)-2 stimulation on the tumor-inhibitory role of the NK cells was measured indirectly by analyzing the expression of various NK cell receptors and activated NK cell markers. It was observed that the NK cells inhibited the proliferation, migration and invasion of the MHCC97-H cells in vitro. Furthermore, the NK cells demonstrated long-term survival in the livers of the nude mice, and inhibited lung metastasis of hepatocellular carcinoma in vivo. However, liver tumor growth was not inhibited by the NK cells. IL-2 was identified to enhance the tumor-inhibitory effect of NK cells. The present study concludes that IL-2 may enhance the antitumor activity of the NK cells, and thereby inhibit the metastases of hepatocellular carcinoma in mice.

Rheumatoid arthritis (RA) is an autoimmune disease characterized by chronic inflammation and synovial hyperplasia leading to progressive joint destruction. Fibroblast-like synoviocytes (FLS) are central components of the aggressive, tumour-like synovial structure termed pannus, which invades the joint space and cartilage. A distinct natural killer (NK) cell subset expressing the inhibitory CD94/NKG2A receptor is present in RA synovial fluid. Little is known about possible cellular interactions between RA-FLS and NK cells. We used cultured RA-FLS and the human NK cell line Nishi, of which the latter expresses an NK receptor repertoire similar to that of NK cells in RA synovial fluid, as an in vitro model system of RA-FLS/NK cell cross-talk. We show that RA-FLS express numerous ligands for both activating and inhibitory NK cell receptors, and stimulate degranulation of Nishi cells. We found that NKG2D, DNAM-1, NKp46 and NKp44 are the key activating receptors involved in Nishi cell degranulation towards RA-FLS. Moreover, blockade of the interaction between CD94/NKG2A and its ligand HLA-E expressed on RA-FLS further enhanced Nishi cell degranulation in co-culture with RA-FLS. Using cultured RA-FLS and the human NK cell line Nishi as an in vitro model system of RA-FLS/NK cell cross-talk, our results suggest that cell-mediated cytotoxicity of RA-FLS may be one mechanism by which NK cells influence local joint inflammation in RA.
© 2014 John Wiley & Sons Ltd.