Tsukasa Nabekura

Natural killer cells: walking three paths down memory lane

Immunological memory has traditionally been regarded as a unique feature of the adaptive immune response, mediated in an antigen-specific manner by T and B lymphocytes. All other hematopoietic cells, including natural killer (NK) cells, are classified as innate immune cells, which have been considered short-lived but can respond rapidly against pathogens in a manner not thought to be driven by antigen. Interestingly, NK cells have recently been shown to survive long term after antigen exposure and subsequently mediate antigen-specific recall responses. In this review, we address the similarities between, and the controversies surrounding, three major viewpoints of NK memory that have arisen from these recent studies: (i) mouse cytomegalovirus (MCMV)-induced memory; (ii) cytokine-induced memory; and (iii) liver-restricted memory cells.

Costimulatory molecule DNAM-1 is essential for optimal differentiation of memory natural killer cells during mouse cytomegalovirus infection.

Recent studies demonstrate that natural killer (NK) cells have adaptive immune features. Here, we investigated the role of the costimulatory molecule DNAM-1 in the differentiation of NK cells in a mouse model of cytomegalovirus (MCMV) infection. Antibody blockade of DNAM-1 suppressed the expansion of MCMV-specific Ly49H(+) cells during viral infection and inhibited the generation of memory NK cells. Similarly, DNAM-1-deficient (Cd226(-/-)) Ly49H(+) NK cells exhibited intrinsic defects in expansion and differentiation into memory cells. Src-family tyrosine kinase Fyn and serine-threonine protein kinase C isoform eta (PKCη) signaling through DNAM-1 played distinct roles in the generation of MCMV-specific effector and memory NK cells. Thus, cooperative signaling through DNAM-1 and Ly49H are required for NK cell-mediated host defense against MCMV infection.

IL-33 Receptor ST2 Amplifies the Expansion of NK Cells and Enhances Host Defense during Mouse Cytomegalovirus Infection

NK cells provide important host defense against viruses and can differentiate into self-renewing memory NK cells after infection, alloantigen stimulation, and cytokine stimulation. In this study, we investigated the role of the IL-33 receptor ST2 in the differentiation of NK cells during mouse CMV (MCMV) infection. Although ST2-deficient (Il1rl1−/−) Ly49H+ NK cells develop normally and differentiate into memory cells after MCMV infection, naive and memory Il1rl1−/− Ly49H+ NK cells exhibited profound defects in MCMV-specific expansion, resulting in impaired protection against MCMV challenge. Additionally, IL-33 enhanced m157 Ag-specific proliferation of Ly49H+ NK cells in vitro. Thus, an IL-33/ST2 signaling axis in NK cells contributes to host defense against MCMV.

Critical role of DNAX accessory molecule-1 (DNAM-1) in the development of acute graft-versus-host disease in mice

Acute graft-versus-host disease (GVHD) is a life-threatening complication following bone marrow transplantation; however, no effective molecular-targeting therapy has been determined. Here, we show that mice that received allogeneic splenocytes deficient in DNAX accessory molecule-1 (DNAM-1) had significantly milder GVHD and lower mortality than those that received allogeneic WT splenocytes. Donor CD8+ T cells deficient in DNAM-1 showed significantly less proliferation and infiltration of the liver and intestines of recipient mice and produced less IFN-γ after coculture with allogeneic splenocytes than WT CD8+ T cells. Mice prophylactically treated with an anti–DNAM-1 antibody showed milder GVHD and lower mortality than those treated with a control antibody. Moreover, treatment with a single administration of the antibody after the overt onset of GVHD ameliorated GVHD and prolonged survival. Finally, we show that the anti–DNAM-1 antibody therapy also ameliorated the overt GVHD in lethally irradiated mice after MHC-matched, minor antigen-mismatched bone marrow transplantation. These results indicate that DNAM-1 plays an important role in the development of GVHD and is an ideal molecular target for therapeutic approaches to GVHD.

Antigen-specific expansion and differentiation of natural killer cells by alloantigen stimulation

Nabekura and Lanier provide evidence that alloantigen stimulation of mouse NK cells promotes the in vivo expansion and generation of memory-like NK cells. NK cells expressing the activating Ly49D receptor preferentially expand and differentiate when challenged with allogeneic cells in an inflammatory environment, but this can be suppressed if NK cells also express the inhibitory Ly49A receptor which recognizes the same ligand. Recall responses were driven by expression of activating Ly49 receptors and regulated by inhibitory MHC I receptors.

Tracking the fate of antigen-specific versus cytokine-activated natural killer cells after cytomegalovirus infection

Nabekura and Lanier demonstrate that two distinct long-lived NK cell subsets with different functional properties differentiate during mouse model of cytomegalovirus (MCMV) infection. NK cells expressing the MCMV-specific Ly49H receptor differentiated into memory NK cells and Ly49H− NK cells differentiated into cytokine-activated NK cells. Memory NK cells show enhanced effector function, whereas cytokine-activated NK cells persisted better in an MCMV-free environment.

The immunoreceptor adapter protein DAP12 suppresses B lymphocyte–driven adaptive immune responses

Human and mouse B cells lacking functional DAP12 are hyperresponsive, and DAP12 works with MAIR-II (CD300d) to negatively regulate B cell activity.

The induction of tumor‐specific CD4+ T cells via major histocompatibility complex class II is required to gain optimal anti‐tumor immunity against B16 melanoma cell line in tumor immunotherapy using dendritic cells

Abstract:  We have demonstrated that dendritic cells (DCs) genetically modified to express tumor‐associated antigens (TAAs) with retroviral vectors elicit more potential anti‐tumor effect than those loaded with peptides because they can prime antigen‐specific CD4+ T cells resulting in production of tumor‐specific antibody. In this study, we showed the importance of antigen presentation via a major histocompatibility complex (MHC) class II molecule in cancer immunity against non‐membrane bound TAAs such as the melanoma antigen gp100 by using DCs derived from MHC class II‐deficient mice (C2KO). DCs were prepared by transduction of gp100 cDNA into haematopoietic progenitor cells obtained from C2KO followed by differentiation with cytokines (C2KO‐gp/DCs). When C2KO‐gp/DCs were inoculated into immunocompetent mice, the mice scarcely primed the antigen‐specific Th1 cells and developed fewer CD8 T cells than did those inoculated with transduced DCs prepared from normal mice. The attenuated anti‐tumor effect was also confirmed in a postimmunization setting where, while two of eight control mice eradicated the pre‐existing melanoma cell line B16 (25%), no mice inoculated with C2KO‐gp/DCs did. These results suggested not only the limitation of current protocols using MHC class I‐restricted tumor peptides but also the usefulness of DCs expressing gp100 in vaccine therapy against melanoma.

Activating Receptors for Self-MHC Class I Enhance Effector Functions and Memory Differentiation of NK Cells during Mouse Cytomegalovirus Infection

Natural killer (NK) cells are important in host defense against pathogens, and they can subsequently differentiate into memory NK cells. The Ly49 and KIR gene families in rodents and humans encode both inhibitory and activating receptors for MHC class I. The physiological role of activating KIR or Ly49 receptors that recognize self-MHC class I during immune response to viral infections is unknown. Here, we address how the activating Ly49D receptor impacts the NK cell response to mouse cytomegalovirus (MCMV) infection by comparing the activation and differentiation of Ly49D-bearing NK cells in mice lacking or expressing H-2D(d), the cognate MHC class I ligand of Ly49D. After MCMV infection, Ly49D augmented IFN-γ production by MCMV-specific Ly49H(+) NK cells and preferentially promoted the generation of memory Ly49H(+) NK cells. Thus, activating receptors for self-MHC class I modulate the differentiation of MCMV-specific NK cells and are beneficial for host defense against MCMV infection.

PPARβ/δ activation of CD300a controls intestinal immunity

Macrophages are important for maintaining intestinal immune homeostasis. Here, we show that PPARβ/δ (peroxisome proliferator-activated receptor β/δ) directly regulates CD300a in macrophages that express the immunoreceptor tyrosine based-inhibitory motif (ITIM)-containing receptor. In mice lacking CD300a, high-fat diet (HFD) causes chronic intestinal inflammation with low numbers of intestinal lymph capillaries and dramatically expanded mesenteric lymph nodes. As a result, these mice exhibit triglyceride malabsorption and reduced body weight gain on HFD. Peritoneal macrophages from Cd300a−/− mice on HFD are classically M1 activated. Activation of toll-like receptor 4 (TLR4)/MyD88 signaling by lipopolysaccharide (LPS) results in prolonged IL-6 secretion in Cd300a−/− macrophages. Bone marrow transplantation confirmed that the phenotype originates from CD300a deficiency in leucocytes. These results identify CD300a-mediated inhibitory signaling in macrophages as a critical regulator of intestinal immune homeostasis.