A major contribution to the genome variability among individuals comes from deletions and duplications - collectively termed copy number variations (CNVs) - which alter the diploid status of DNA. These alterations may have no phenotypic effect, account for adaptive traits or can underlie disease. We have compiled published high-quality data on healthy individuals of various ethnicities to construct an updated CNV map of the human genome. Depending on the level of stringency of the map, we estimated that 4.8-9.5% of the genome contributes to CNV and found approximately 100 genes that can be completely deleted without producing apparent phenotypic consequences. This map will aid the interpretation of new CNV findings for both clinical and research applications.

A copy number variation map of the human genome

The activating natural killer (NK)-cell receptor KIR3DS1 has been linked to the outcome of various human diseases, including delayed progression of disease caused by human immunodeficiency virus type 1 (HIV-1), yet a ligand that would account for its biological effects has remained unknown. We screened 100 HLA class I proteins and found that KIR3DS1 bound to HLA-F, a result we confirmed biochemically and functionally. Primary human KIR3DS1(+) NK cells degranulated and produced antiviral cytokines after encountering HLA-F and inhibited HIV-1 replication in vitro. Activation of CD4(+) T cells triggered the transcription and surface expression of HLA-F mRNA and HLA-F protein, respectively, and induced binding of KIR3DS1. HIV-1 infection further increased the transcription of HLA-F mRNA but decreased the binding of KIR3DS1, indicative of a mechanism for evading recognition by KIR3DS1(+) NK cells. Thus, we have established HLA-F as a ligand of KIR3DS1 and have demonstrated cell-context-dependent expression of HLA-F that might explain the widespread influence of KIR3DS1 in human disease.

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Open conformers of HLA-F are high-affinity ligands of the activating NK-cell receptor KIR3DS1

The genetic factors associated with susceptibility or resistance to viral infections are likely to involve a sophisticated array of immune-response. These genetic elements may modulate other biological factors that account for significant influence on the gene expression and/or protein function in the host. Among them, the role of the Major Histocompatibility Complex (MHC) in viral pathogenesis in particular HIV and HCV, is very well documented. We recently added a novel insight into the field by identifying the molecular mechanism associated with the protective role of HLA-B27/B57 CD8+ T cells in the context of HIV-1 infection and why these alleles act as a double-edged sword protecting against viral infections but predisposing the host to autoimmune diseases. The focus of this review will be reexamining the role of classical and non-classical HLA-alleles including class Ia (HLA-A, -B, -C), class Ib (HLA-E, -F, -G, -H) and class II (HLA-DR, -DQ, -DM, and -DP) in immune regulation and viral pathogenesis (e.g. HIV and HCV). To our knowledge this is the very first review of its kind to comprehensively analyze the role of these molecules in immune regulation associated with chronic viral infections.

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Human Leukocyte Antigen (HLA) and Immune Regulation: How Do Classical and Non-Classical HLA Alleles Modulate Immune Response to Human Immunodeficiency Virus and Hepatitis C Virus Infections?

NK cells recognize self-HLA via killer Ig-like receptors (KIR). Homeostatic HLA expression signals for inhibition via KIR, and downregulation of HLA, a common consequence of viral infection, allows NK activation. Like HLA, KIR are highly polymorphic, and allele combinations of the most diverse receptor-ligand pair, KIR3DL1 and HLA-B, correspond to hierarchical HIV control. We used primary cells from healthy human donors to demonstrate how subtype combinations of KIR3DL1 and HLA-B calibrate NK education and their consequent capacity to eliminate HIV-infected cells. High-density KIR3DL1 and Bw4-80I partnerships endow NK cells with the greatest reactivity against HLA-negative targets; NK cells exhibiting the remaining KIR3DL1/HLA-Bw4 combinations demonstrate intermediate responsiveness; and Bw4-negative KIR3DL1(+) NK cells are poorly responsive. Cytotoxicity against HIV-infected autologous CD4(+) T cells strikingly correlated with reactivity to HLA-negative targets. These findings suggest that the programming of NK effector function results from defined features of receptor and ligand subtypes. KIR3DL1 and HLA-B subtypes exhibit an array of binding strengths. Like KIR3DL1, subtypes of HLA-Bw4 are expressed at distinct, predictable membrane densities. Combinatorial permutations of common receptor and ligand subtypes reveal binding strength, receptor density, and ligand density to be functionally important. These findings have immediate implications for prognosis in patients with HIV infection. Furthermore, they demonstrate how features of KIR and HLA modified by allelic variation calibrate NK cell reactive potential.

KIR3DL1 and HLA-B Density and Binding Calibrate NK Education and Response to HIV

Understanding how human genetics influence infectious disease susceptibility offers the opportunity for new insights into pathogenesis, potential drug targets, risk stratification, response to therapy and vaccination. As new infectious diseases continue to emerge, together with growing levels of antimicrobial resistance and an increasing awareness of substantial differences between populations in genetic associations, the need for such work is expanding. In this Review, we illustrate how our understanding of the host-pathogen relationship is advancing through holistic approaches, describing current strategies to investigate the role of host genetic variation in established and emerging infections, including COVID-19, the need for wider application to diverse global populations mirroring the burden of disease, the impact of pathogen and vector genetic diversity and a broad array of immune and inflammation phenotypes that can be mapped as traits in health and disease. Insights from study of inborn errors of immunity and multi-omics profiling together with developments in analytical methods are further advancing our knowledge of this important area.

Host genetics and infectious disease: new tools, insights and translational opportunities.

Natural killer (NK) cells have emerged as pivotal players in innate immunity, especially in the defense against viral infections and tumors. Killer immunoglobulin-like receptors (KIRs) – an important recognition receptor expressed on the surface of NK cells – regulate the inhibition and/or activation of NK cells after interacting with human leukocyte antigen (HLA) class I ligands. Various KIR genes might impact the prognosis of many different diseases. The implications of KIR-HLA interaction in HIV disease progression remains poorly understood. Here, we studied KIR genotypes, mRNA levels, HLA genotypes, CD4+ T cell counts and viral loads in our cohort of Human Immunodeficiency Virus (HIV)-infected individuals, a group that includes HIV long-term nonprogressors (LTNPs) and typical progressors (TPs). We found that the frequency of KIR3DS1/L1 heterozygotes with HLA-Bw4-80I gene was much higher in LTNPs than in TPs (P = 0.001) and that the KIR3DL1 homozygotes without HLA-Bw4-80I gene had higher viral loads and lower CD4+ T cell counts (P = 0.014 and P = 0.021, respectively). Our study also confirmed that homozygosity for the HLA-Bw6 allele was associated with rapid disease progression. In addition to the aforementioned results on the DNA level, we observed that higher level expression of KIR3DS1 mRNA was in LTNP group, and that higher level expression of KIR3DL1 mRNA was in TP group. Our data suggest that different KIR-HLA genotypes and different levels of transcripts associate with HIV disease progression.

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Chen Cui

Papers

KIR3DS1/L1 and HLA-Bw4-80I are associated with HIV disease progression among HIV typical progressors and long-term nonprogressors