Enhancement of cytokine‐driven NK cell IFN‐γ production after vaccination of HCMV infected Africans

Human cytomegalovirus (HCMV) infection drives the phenotypic and functional differentiation of NK cells, thereby influencing the responses of these cells after vaccination. NK cell functional differentiation is particularly advanced in African populations with universal exposure to HCMV. To investigate the impact of advanced differentiation on vaccine‐induced responses, we studied NK‐cell function before and after vaccination with Trivalent Influenza Vaccine (TIV) or diphtheria, tetanus, pertussis, inactivated poliovirus vaccine (DTPiP) in Africans with universal, lifelong HCMV exposure. In contrast to populations with lower prevalence of HCMV infection, no significant enhancement of NK‐cell responses (IFN‐γ, CD107a, CD25) occurred after in vitro re‐stimulation of post‐vaccination NK cells with TIV or DTPiP antigens compared to pre‐vaccination baseline cells. However, both vaccinations resulted in higher frequencies of NK cells producing IFN‐γ in response to exogenous IL‐12 with IL‐18, which persisted for up to 6 months. Enhanced cytokine responsiveness was restricted to less differentiated NK cells, with increased frequencies of IFN‐γ⁺ cells observed within CD56^brightCD57^?, CD56^dimCD57^?NKG2C^? and CD56^dimCD57^?NKG2C⁺ NK‐cell subsets. These data suggest a common mechanism whereby different vaccines enhance NK cell IFN‐γ function in HCMV infected donors and raise the potential for further exploitation of NK cell “pre‐activation” to improve vaccine effectiveness.     

Selective depletion of CD56(dim) NK cell subsets and maintenance of CD56(bright) NK cells in treatment-naive HIV-1-seropositive individuals

Human immunodeficiency virus-1 (HIV-1) infected patients show a gradual loss of natural killer (NK) cells that correlates with disease progression. However, the effect of HIV-1 infection on different NK cell subsets has not been fully characterized. In healthy individuals most NK cells are CD3^–CD56⁺ and two different subpopulations, CD56^dim and CD56^bright, can be distinguished by the mean fluorescence intensity. Although it was originally suggested that CD56^bright NK cells represent the precursors of the CD56^dim subpopulation, recent cumulative data indicate that CD56^bright and CD56^dim NK cells are phenotypically, functionally, and developmentally different NK cell subsets. In this study, the analysis of CD56^bright and CD56^dim NK subsets showed that neither the number nor the phenotype of CD56^bright NK cells were significantly altered in treatment-naive HIV-1-infected individuals, whereas the number of CD56^dim NK cells was decreased. We also have studied NK cell subsets defined by the expression of CD56 in combination with CD16, CD161, or CD94 molecules. Our results demonstrated a preferential decrease of CD3^–CD56⁺ NK cells coexpressing CD16 and CD161 but lacking CD94 molecules. On the contrary an increased percentage of NK cells that do not express CD56 molecules but express CD16, CD161, or CD94 was also found in HIV-1-infected individuals. As it has been proposed that these CD56-negative NK cells expressing other NK cell receptors represent immature NK cells with low cytolytic capacity, our results support that a defective differentiation from immature CD56 negative NK cells to mature CD56^dim NK cells occurs in HIV-1 infection.     

Poor memory B cell generation contributes to non-protective responses to DTaP vaccine antigens in otitis-prone children

We recently identified a cohort of children with recurrent episodes of acute otitis media (AOM) who fail to generate protective antibody titres to otopathogens and several vaccine antigens. In this study we determined the antibody levels against DTaP vaccine antigens, diphtheria toxoid (DT), tetanus toxoid (TT) and acellular pertussis toxoid (PT) in sera from 15 stringently defined otitis-prone (sOP) children and 20 non-otitis-prone (NOP) children. We found significantly lower concentrations of immunoglobulin (Ig)G antibodies against vaccine antigens in the serum of sOP children compared to age-matched NOP children. To elucidate immunological cellular responses to the vaccines in these children, we investigated memory B cell responses to DTaP vaccination. We used fluorescently conjugated vaccine antigens to label antigen receptors on the surface of memory B cells and examined the frequency of antigen-specific CD19⁺ CD27⁺ memory B cells in the peripheral blood. sOP children showed a significantly lower percentage of antigen-specific CD19⁺ CD27⁺ memory B cells than NOP children. We also found a linear correlation between the frequencies of memory B cells and circulating IgG titres for DT, TT and PT proteins. To our knowledge, this is the first study to show significant differences in memory B cell responses to DTaP vaccine antigens and their correlation with the circulating antibodies in young children with recurrent AOM.     

Substance P primes lipoteichoic acid- and Pam3CysSerLys4-mediated activation of human mast cells by up-regulating Toll-like receptor 2

We investigated the distribution of natural killer (NK) cell subsets, their activating and inhibitory receptors, and their cytolytic potential, in primary human immunodeficiency virus (HIV)-infected (PHI) individuals at baseline and during 1 year of follow-up with or without antiretroviral therapy, and compared the results with those obtained in treatment-naïve, chronically HIV-infected (CHI) individuals, and HIV-seronegative (HN) healthy individuals. The proportion of the CD56^dim and CD56^bright subsets decreased with disease progression, whereas that of the CD56⁻ CD16⁺ subset increased. In the CD56^dim subset, the proportion of cells with natural cytotoxicity receptors (NCRs) decreased with disease progression, and their cytolytic potential was reduced. Conversely, the CD56^bright subset was characterized by a high proportion of NCR-positive, killer cell immunoglobulin-like receptor (KIR)-positive NKG2A⁺ cells in both CHI and PHI individuals, which was associated with an increase in their cytolytic potential. During the 1 year of follow-up, the PHI individuals with high viraemia levels and low CD4⁺ T-cell counts who received highly active antiretroviral therapy (HAART) had a similar proportion of NK subsets to CHI individuals, while patients with low viraemia levels and high CD4⁺ T-cell counts who remained untreated had values similar to those of the HN individuals. Our results indicate a marked perturbation of the NK cell compartment during HIV-1 infection that is multifaceted, starts early and is progressive, primarily involves the CD56^bright subset, and is partially corrected by effective HAART.     

Coordinated expansion of both memory T cells and NK cells in response to CMV infection in humans

NK cells are key players in the fight against persistent viruses. Human cytomegalovirus (HCMV) infection is associated with the presence of a population of CD16⁺ CD56^dim NKG2C⁺ NK cells in both acutely and latently infected individuals. Here, we studied the nature of these terminally differentiated NK cells in different human populations infected with HCMV: healthy donors stratified by age, thymectomized individuals, pregnant women suffering from primary CMV infection, and lung transplant patients. Both CD16⁺ CD56^dim NK‐ and CD8 T‐cell phenotypes as well as functional capacities were determined and stratified according to age and/or CMV event. Similarly to T‐cell responsiveness, we observe an accumulation over time of NKG2C⁺ NK cells, which preferentially expressed CD57. This accumulation is particularly prominent in elderly and amplified further by CMV infection. Latent HCMV infection (without replication) is sufficient for NKG2C⁺ CD57⁺ NK cells to persist in healthy individuals but is not necessarily required in old age. Collectively, the present work supports the emerging concept that CMV shapes both innate and adaptive immunity in humans.     

Impaired natural killer cell‐induced antibody‐dependent cell‐mediated cytotoxicity is associated with human immunodeficiency virus‐1 disease progression

This study evaluates the correlation between natural killer (NK) cell function and human immunodeficiency virus (HIV)-1 disease progression in 133 untreated HIV-1 positive Chinese subjects, including 41 former plasma donors (FPDs) and 92 men who have sex with men, and 35 HIV-negative controls. Flow cytometry was used to determine the abundance of NK cell subsets, the expression levels of receptor species, human leucocyte antigen (HLA) genotyping and the antibody-dependent cell-mediated cytotoxicity (ADCC) responses of NK cells. We observed a decreased expression of CD56^dimCD16⁺ NK cell subsets and an increased expression of CD56⁻CD16⁺ with HIV-1 infection. As well, the expression of activating and inhibitory receptors increased significantly in NK cells, but CD16 receptor levels and the NKG2A/NKG2C ratio were down-regulated with HIV-1 infection. ADCC responses were higher in elite controllers than in all other groups, and were correlated inversely with HIV-1 viral load but correlated positively with CD4 count only in FPDs. Furthermore, individuals infected for < 1 year have lower ADCC responses than those infected for > 1 year. We also observed a negative association between ADCC responses and viral load in those who carry the HLA-A*30/B*13/Cw*06 haplotype. The positive correlation between CD16 expression and ADCC responses and a negative correlation trend between CD158a and ADCC responses were also observed (P = 0·058). Our results showed that the ADCC response is associated with patients'' disease status, receptor expression levels, infection time and specific HLA alleles, which indicates that ADCC may offer protective effects against HIV-1 infection.     

CD56bright natural killer cell subsets: Characterization of distinct functional responses to interleukin-2 and the c-kit ligand

Natural killer (NK) cells are bone marrow-derived large granular lymphocytes that express the CD56 surface antigen. The CD56^bright NK subset represents approximately 10 % of all NK cells and is thought to be the least differentiated NK cell component in blood. The most mature NK cell expresses CD56 at low density and CD16 (FcRγIII) at high density, whereas CD56^bright NK cells either lack CD 16 (CD56^brightCD16^?) or express it at low density (CD56^brightCD16^dim). c-kit is a tyrosine kinase receptor which is expressed on both CD34⁺ hemato-poietic precursor cells and CD56^bright NK cells. In the current study, we characterize interleukin (IL)-2 receptor (IL-2R) and c-kit expression in each of the CD56^bright subsets. Both the CD56^brightCD16^? and CD56^brightCD16^dim NK subsets express the high-affinity IL-2R and the c-kit receptor when isolated from fresh blood. However, each CD56^bright NK cell subset has distinct functional responses to IL-2, the c-kit ligand (KL), or both. Activation of the high-affinity IL-2R on CD56^brightCD16^? NK cells induces a proliferative response that is significantly weaker than that observed in the CD56^brightCD16^dim NK cell subset. Incubation of the CD56^brightCD16^? NK cell subset with KL significantly enhances IL-2-induced proliferation, while KL has no such effect on the CD56^brightCD16^dim NK subset. Activation of the high-affinity IL-2R in both CD56^bright subsets induces lymphokine-activated killer (LAK) activity, but the addition of KL has no effect on LAK activity. Co-stimulation of either CD56^bright subset with IL-12 and concentrations of IL-2 that only saturate the high-affinity IL-2R induces substantial interferon (IFN)-γ production. The addition of KL to this co-stimulatory signal enhances IFN-γ production in both CD56^bright NK subsets. The distinct functional responses to IL-2 and KL seen in the CD56^brightCD16^? and CD56^brightCD16^dim NK subsets provide insight into IL-2R signaling and suggest that each phenotype identifies a discrete stage of NK cell differentiation.     

Tissue Distribution Dynamics of Human NK Cells Inferred from Peripheral Blood Depletion Kinetics after Sphingosine‐1‐Phosphate Receptor Blockade

Human natural killer (NK) cell subsets differentially distribute throughout the organism. While CD56^dim and CD56^bright NK cell subsets similarly reside in the bone marrow (BM), the CD56^dim population predominantly accumulates in non‐lymphoid tissues and the CD56^bright counterpart in lymphoid tissue (LT). The dynamics with which these NK cell subsets redistribute to tissues remains unexplored. Here, we studied individuals newly exposed to fingolimod, a drug that efficiently blocks sphingosine‐1‐phosphate (S1P)‐directed lymphocyte – including NK cell – egress from tissue to blood. During an observation period of 6h peripheral blood depletion of CD56^bright NK cells was observed 3 h after first dose of fingolimod, with 40–50% depletion after 6 h, while a decrease of the numbers of CD56^dim NK cells did not reach the level of statistical significance. In vitro, CD56^bright and CD56^dim NK cells responded comparably to the BM‐homing chemokine CXCL12, while CD56^bright NK cells migrated more efficiently in gradients of the LT‐homing chemokines CCL19 and CCL21. In conjuncture with these in vitro studies, the indirectly observed subset‐specific depletion kinetics from blood are compatible with preferential and more rapid redistribution of CD56^bright NK cells from blood to peripheral tissue such as LT and possibly also the inflamed central nervous system. These data shed light on an unexplored level at which access of NK cells to LT, and thus, for example antigen‐presenting cells, is regulated.     

Impaired circulating CD56dim NK cells are associated with decompensation of HBV-related cirrhosis

NK cells play an important role in immune regulation and defense of infection, but their characteristics in patients with decompensated cirrhosis and their relationship with liver function remain unclear. We studied the functional properties of NK cells (including CD56^dim NK and CD56^bright NK cells) in patients with HBV-related decompensated liver cirrhosis (HBV-DLC) and analyzed their relationship with decompensation of liver function. Thirty patients with HBV-DLC and 25 patients with HBV-related compensated liver cirrhosis (HBV-CLC) were recruited in this study. Twenty five age- and sex-matched healthy individuals were recruited as healthy controls (HCs). The phenotypical and functional characteristics of NK cell subsets were detected by flow cytometry, and the correlation between NK cells and decompensation of liver function was analyzed. The frequency of circulating CD56^bright NK cells was significantly increased while circulating CD56^dim NK cells was significantly decreased in HBV-DLC patients as compared with HCs and HBV-CLC patients. Peripheral activated-CD56^bright NK cells from HBV-DLC patients might express lower levels of inhibitory receptor CD158b1/2 and higher levels of activating receptor NKG2D and their expression of perforin and granzyme A/B also increased significantly compared with HCs, suggesting a high immune activation status of peripheral CD56^bright NK cells in HBV-DLC patients. In HBV-DLC patients, the expression of CD107a and perforin in circulating CD56^dim NK cells was positively correlated with cytolytic capacity while CD107a and perforin expression in circulating CD56^dim NK cells were significantly decreased, suggesting an impaired cytolytic capacity of circulating CD56^dim NK cells. Besides, we found that the perforin expression of circulating CD56^dim NK cells correlated negatively with child-pugh classification in HBV-DLC patients. The functional properties of circulating NK cell subsets in HBV-DLC patients have changed significantly, especially of CD56^dim NK cells which closely related to decompensation of liver function. These findings may help provide new perspectives and theoretical basis for the treatment of patients with HBV-DLC.     

Effects of the NK Cell Recovery on Outcomes of Unmanipulated Haploidentical Blood and Marrow Transplantation for Patients with Hematologic Malignancies

The goal of this study was to investigate the association of natural killer (NK) cell recovery with clinical outcomes after unmanipulated haploidentical blood and marrow transplantation. We sequentially monitored the reconstitution kinetics of circulating NK cells, CD56^bright and CD56^dim, in 43 patients by flow cytometry, and the functionality recovery of cytokine or cytotoxicity of NK cells by flow cytometry or lactate dehydrogenase release assay after transplantation. Reconstitution of NK cells was rapid but accompanied by skewing of cell subsets mainly in CD56^bright, which recovered earlier. Linear regression analysis demonstrated that dose of CD34⁺ cells in the allografts was inversely correlated with the ratio of T/NK cells (β = −0.506, P = .003) and CD56^dim/CD56^bright cell (β = −.403, P = .018) by day 14 after hematopoietic stem cell transplantation (HSCT), and the dose of CD3⁺ T cells in the allografts was also inversely correlated with the ratio CD56^dim/CD56^bright cells by day 14 after HSCT (β = −0.474, P = .005). Moreover, the dose of CD56^dim NK cells in the allograft was positively associated with the day 14 CD56^brigh NK cells (β = 0.494, P = .032) and inversely correlated with the day 14 ratio of CD56^dim/CD56^bright cells (β = −0.617, P = .005). Compared with nonacute graft-versus-host disease (GVHD) patients, patients with acute GVHD (aGVHD) had a higher level of NK subsets during week 2 posttransplantation. Cox regression analysis revealed that the patients with more CD56^bright NK cells in the recovery stage had a higher survival rate (hazard risk [HR], 0.406; P = .017) and the patients with a higher ratio of T/NK (>1.0) had a higher chance of getting aGVHD (HR, 3.436; P = .059) and chronic GVHD (HR, 3.925; P = .028). Our results suggest that the recovery of NK cells is and can be used as an indicator to predicate the clinical outcomes after unmanipulated haploidentical transplantation.     

Evidence of sex-based differences in natural killer cell responses to exercise and carbohydrate intake in children

Distinct natural killer (NK) cell subsets (CD56^bright and CD56^dim) are mobilized with exercise and these cells may serve adaptive functions. We determined the distribution of NK cell subsets in response to exercise and carbohydrate (CHO) intake in young girls and compared these responses with previous findings in young boys of the same age. Twelve girls (12 years old) cycled for 60 min at 70% while drinking 6% CHO or flavoured water. Blood was collected at rest, during (30 and 60 min) and following (30 and 60 min) exercise to identify NK cells as CD3⁻CD56^bright or CD3⁻CD56^dim. CD69 expression on total CD3⁻CD56⁺ cells was also determined. A trend (P = 0.07) was found for a trial × time interaction in CD56^dim cell counts, with values lower with CHO than with water. CHO intake did not influence CD56^bright responses (P ≥ 0.39). The CD56^bright:CD56^dim ratio increased during recovery from exercise (P < 0.001), compared to rest, with no effect of CHO intake (P = 0.48). CD69 expression was not different between exercise or recovery and rest. Like young boys, girls experience an elevated CD56^bright:CD56^dim ratio during recovery from exercise and CHO intake attenuates the exercise-induced CD56^dim but not CD56^bright cell response. Unlike young boys, girls do not experience a CHO-induced increase in the CD56^bright:CD56^dim ratio during recovery and CD69 expression does not increase on CD3⁻CD56⁺ cells during recovery. We conclude that even in young children sex-based differences exist in the NK cell response to exercise and CHO intake.     

Functional impairment in circulating and intrahepatic NK cells and relative mechanism in hepatocellular carcinoma patients

Functional defects in natural killer (NK) cells have been proposed to be responsible for the failure of anti-tumor immune responses. Whether and how NK cells are impaired in hepatocellular carcinoma (HCC) patients remain unknown. In this study, we found that HCC patients displayed a dramatic reduction in peripheral CD56^dimCD16^pos NK subsets compared with healthy subjects. A significant reduction of CD56^dimCD16^pos NK subsets was also found in tumor regions compared with non-tumor regions in the livers of these HCC patients. Both these peripheral and tumor-infiltrating NK cells exhibited poorer capacity to produce IFN-γ and kill K562 targets, which was further found to be associated with increased CD4⁺CD25⁺ T regulatory cells as we previously-described in HCC patients. Addition of Tregs from HCC patients efficiently inhibited the anti-tumor ability of autologous NK cells in vitro. These findings are helpful for understanding the mechanism of NK cell-mediated anti-tumor immune responses in HCC patients.     

Impaired natural killer cell subset phenotypes in human obesity

Obesity is associated with alterations in functionality of immune cells, like macrophages and natural killer (NK) cells, leading to an increased risk for severe infections and several cancer types. This study aimed to examine immune cell populations and functional NK cell parameters focusing on NK cell subset phenotypes in normal-weight and obese humans. Therefore, peripheral blood mononuclear cells (PBMCs) were isolated from normal-weight and obese individuals and analyzed by flow cytometry. Results show no significant changes in the frequency of monocytes, B lymphocytes, or NKT cells but a significantly increased frequency of T lymphocytes in obesity. The frequency of total NK cells was unaltered, whereas the number of low cytotoxic CD56^bright NK cell subset was increased, and the number of high cytotoxic CD56^dim NK cell subset was decreased in obese subjects. In addition, the frequency of CD56^bright NK cells expressing the activating NK cell receptor NKG2D as well as intracellular interferon (IFN)-γ was elevated in the obese study group. In contrast, the frequency of NKG2D- and IFN-γ-positive CD56^dim NK cells was lower in obesity compared to normal-weight individuals. Moreover, the expression of the activation marker CD69 was decreased in NK cells, which can be attributed to a reduction of CD69-positive CD56^dim NK cells in obese subjects. In conclusion, data reveal an impaired NK cell phenotype and NK cell subset alterations in obese individuals. This NK cell dysfunction might be one link to the higher cancer risk and the elevated susceptibility for viral infections in obesity.     

Increased proportion of the CD56bright NK cell subset in patients chronically infected with hepatitis C virus (HCV) receiving interferon‐αand ribavirin therapy

Natural killer (NK) cells are implicated in the regulation of a protective immune response in patients chronically infected with hepatitis C virus (HCV), but effects of interferon‐α/ribavirin therapy on NK cell subsets and the consequences of viral clearance during therapy remain unclear. Samples were collected from chronically infected patients (n = 34) at baseline and from a subset after 3–10 months on pegylated interferon‐α and ribavirin therapy (n = 19). NK cells present in cryopreserved PBMC were characterized by flow cytometry. Before therapy, the frequency of CD3?CD56+ NK cells was lower in patients than uninfected controls. Therapy increased proportions of CD56^bright NK cells. Frequencies of CD56^dim NK cells declined slightly while perforin and CD16 expression on CD56^dim NK cells decreased compared to baseline samples. Evaluation of NK cell subsets at baseline did not identify patients able to achieve sustained virological response following therapy. However, therapy may promote the expansion of NK cells able to produce interferon‐γ, while minimizing cytotoxicity to limit liver damage. J. Med. Virol. 82:568–574, 2010. © 2010 Wiley‐Liss, Inc.     

CD56bright natural killer (NK) cells: an important NK cell subset

Human natural killer (NK) cells can be subdivided into different populations based on the relative expression of the surface markers CD16 and CD56. The two major subsets are CD56^bright CD16^dim/− and CD56^dim CD16⁺, respectively. In this review, we will focus on the CD56^bright NK cell subset. These cells are numerically in the minority in peripheral blood but constitute the majority of NK cells in secondary lymphoid tissues. They are abundant cytokine producers but are only weakly cytotoxic before activation. Recent data suggest that under certain conditions, they have immunoregulatory properties, and that they are probably immediate precursors of CD56^dim NK cells. CD56^bright NK cell percentages are expanded or reduced in a certain number of diseases, but the significance of these variations is not yet clear.     

Early changes of the kinetics of monocyte trem-1 reflect final outcome in human sepsis

Background

Up to 40% of HIV-infected individuals receiving Highly Active Antiretroviral Therapy (HAART) have poor CD4+ T-cell recovery. The role of natural killer (NK) cells in immune recovery during HAART is not well understood. We described the profiles of NK cell subsets and their expression of activating receptor, NKG2D and cytotoxicity receptor NKp46 among suboptimal immune responders to despite four years of suppressive HAART.

Methods

A case control study utilized frozen peripheral blood mononuclear cells (PBMC) from a cohort of HIV-infected adults that initiated HAART in 2004/5, at CD4 < 200 cells/μl. Cases were ‘suboptimal’ responders; patients within the lowest quartile of CD4+ T-cell reconstitution, with a median CD4 count increase of 129 (-43-199) cells/μl (difference between CD4 count at baseline and after 4 years of HAART) and controls were ‘super-optimal’ responders; patients within the highest quartile of CD4 T-cell reconstitution with a median CD4 count increase of 528 (416-878) cells/μl). Expression of NK cell lineage markers (CD56^+/-CD16^+/-) and receptors NKG2D and NKp46, was measured among PBMC from 29 cases of ‘suboptimal’ responders’ and 23 controls of ‘super-optimal responders’, and compared among ‘suboptimal’ and ‘super-optimal’ responders. NK cell populations were compared using the Holm Sidak multiple comparison test and p values < 0.05 were considered statistically significant. Data was analyzed using FLOWJO and GraphPad Prism 6.

Results

‘Suboptimal responders’ had a higher proportion of cytokine producing CD56⁺⁺CD16^+/- (CD56^bri) NK cells than the ‘super-optimal responders’ p = 0.017, and CD56^neg NK cells were lower among suboptimal than super-optimal responders (p = 0.007). The largest NK cell subset, CD56^dim, was comparable among suboptimal responders and ‘super-optimal immune responders’. Expression of NKG2D and NKp46 receptors on NK cell subsets (CD56^bri, CD56^neg and CD56^dim), was comparable among ‘suboptimal’ and ‘super-optimal’ immune responders.

Conclusions

The pro-inflammatory CD56⁺⁺CD16^-- NK cells were higher among ‘suboptimal’ responders relative to ‘super-optimal’ responders, despite four years of suppressive HAART. Alteration of NK cell populations could inhibit host immune responses to infections among suboptimal responders. We recommend further analysis of NK cell function among suboptimal immune responders in order to inform targeted interventions to optimize immune recovery among HAART-treated adults.     

Dynamic change in natural killer cell type in the human ocular mucosa in situ as means of immune evasion by adenovirus infection

The most severe form of virus-induced inflammation at the ocular surface is epidemic keratoconjunctivitis (EKC), often caused by group D human adenoviruses (HAdVs). We investigated the dynamics and mechanisms of changes in natural killer (NK) cell types in the human ocular mucosal surface in situ over the course of infection. In the acute phase of infection, the mature CD56^dimNK cells that comprise a major subpopulation in the normal human conjunctiva are replaced by CD56^brightNK cells recruited to the ocular surface by chemokines produced by the infected epithelium, and NKG2A-expressing CD56^dim and CD56^bright NK cells become the major subpopulations in severe inflammation. These NK cells attracted to the mucosal surface are however incapable of mounting a strong antiviral response because of upregulation of the inhibitory ligand human leukocyte antigen-E (HLA-E) on infected epithelium. Furthermore, group D HAdVs downregulate ligands for activating NK cell receptors, thus rendering even the mature NKG2A⁻NK cells unresponsive, an immune-escape mechanism distinct from other adenoviruses. Our findings imply that the EKC-causing group D HAdVs utilize these multiple pathways to inhibit antiviral NK cell responses in the initial stages of the infection.     

Murine CXCR3+CD27bright NK cells resemble the human CD56bright NK‐cell population

Human NK cells can be subdivided into CD56^dim and CD56^bright NK cells, which exhibit different phenotypical and functional characteristics. As murine NK cells lack CD56 or a distinct correlate, direct comparative studies of NK cells in mice and humans are limited. Although CD27 is currently proposed as a feasible subset marker in mice, we assume that the usage of this marker alone is insufficient. We rather investigated the expression of the chemokine receptor CXCR3 for its suitability for distinguishing murine NK‐cell subsets with simultaneous consideration of CD27. Compared with CXCR3^? NK cells, exerting stronger cytotoxic capability, CXCR3⁺ NK cells displayed an activated phenotype with a lower expression of Ly49 receptors, corresponding to human CD56^bright NK cells. Also in common with human CD56^bright NK cells, murine CXCR3⁺ NK cells exhibit prolific expansion as well as robust IFN‐γ, TNF‐α and MIP‐1α production. We additionally demonstrated changes in both CXCR3 and CD27 expression upon NK‐cell activation. In summary, CXCR3 serves as an additional applicable marker for improved discrimination of functionally distinct murine NK‐cell subsets that comply with those in humans.