Increased natural killer T-like cells are a major source of pro-inflammatory cytokines and granzymes in lung transplant recipients

Background and objective: Natural killer T (NKT)‐like cells are a small but significant population of T lymphocytes; however, their role in lung transplant and the effect of current immunosuppressive agents on their function is largely unknown. We have previously shown lung transplant rejection was associated with an increase in peripheral blood T cell γ‐interferon (IFN‐γ), tumour necrosis factor‐α (TNF‐α) and granzyme B. NKT‐like cells are a source of these pro‐inflammatory mediators and as such may be involved in lung transplant pathology. Methods: We analysed NKT‐like cell numbers and cytokine and granzyme profiles in peripheral blood from a group of stable lung transplant patients and control subjects using multiparameter flow cytometry. Results: There was a significant increase in NKT‐like cells in transplant patients compared with control subjects (6.8 ± 4.9 vs 0.8 ± 0.2% lymphocytes respectively). There was an increase in the numbers of NKT‐like cells producing IFN‐γ, TNF‐α, IL‐2 IL‐17, granzyme and perforin in transplant patients compared with controls. Immunosuppressant drugs were less effective at inhibiting IFN‐γ and TNF‐α production by T and NKT‐like cells than NK cells in vitro. Conclusions: Current therapeutics is inadequate at suppressing NKT‐like cell numbers and their production of pro‐inflammatory mediators known to be associated with graft rejection. Alternative therapies that specifically target NKT‐like cells may improve patient morbidity.     

Alterations in natural killer cells and natural killer T cells during acute viral hepatitis E

The mechanism of liver damage in acute hepatitis E is poorly understood. In this study, we assessed the frequency and activation status of natural killer (NK) and natural killer T (NKT) cells and cytotoxic activity of NK cells in the peripheral blood mononuclear cells (PBMCs) obtained from patients with hepatitis E (n = 41) and healthy controls (n = 61). Flow cytometry was used to assess NK (CD3(-)/CD56(+)) and NKT cell (CD3(+)/CD56(+)) fractions (% of PBMCs) and activation status (CD69(+); % of NK, NKT cells). NK cell cytotoxicity was assessed using major histocompatibilities complex-deficient K562 cells as target cells. In 14 patients, the studies were repeated during the convalescence period. Patients had fewer median (range) NK cells [8.9% (2.4-47.0) vs 11.2% (2.6-35.4)] and NKT cells [8.7% (2.8-34.1) vs 13.6% (2.3-36.9)] than controls (P < 0.05 each). Activation markers were present on large proportion of NK cells [43.5% (11.2-58.6) vs 15.5% (3.0-55.8)] and NKT cells [41.5% (17.4-71.1) vs 12.8% (3.3-63.2); P < 0.05 each] from patients. NK cell cytotoxicity was similar in patients and controls. During convalescence, all the parameters normalized. In conclusion, reversible alterations in NK and NKT cell number and activation status during acute hepatitis E suggest a role of these cells in the pathogenesis of this disease.     

Sustained response to interferon-α plus ribavirin therapy for chronic hepatitis C is closely associated with increased dynamism of intrahepatic natural killer and natural killer T cells

Aim:  Previous studies have revealed that functional impairment of innate immune cells, including natural killer (NK) and natural killer T (NKT) cells, might be associated with the persistence of hepatitis C virus (HCV) infection. However, the involvement of innate immune cells, which predominate in the liver, in therapeutic HCV clearance is still unclear.
Methods:  To clarify the role of intrahepatic innate immune cells in the clinical outcome of patients with chronic hepatitis C (CHC) treated with interferon-α plus ribavirin (IFN/RBV), we prospectively investigated the status of NK and NKT cells in paired liver biopsy and peripheral blood (PB) samples obtained from 21 CHC patients before and immediately after IFN/RBV treatment by flow cytometry. Normal liver and PB samples were obtained from 10 healthy donors for living donor liver transplantation.
Results:  Before treatment, intrahepatic NK and NKT cells constituted a significantly lower proportion in CHC patients than in healthy individuals ( P  < 0.05). After IFN/RBV treatment, the proportions and absolute numbers of CD3^-CD161⁺ NK and CD3⁺CD56⁺ NKT cells in the liver, but not in PB, were significantly increased in sustained responders (SR) as compared with poor responders ( P  < 0.05). The proportion of CD3⁺CD161⁺ NKT cells was also increased in the liver of SR after the treatment. Moreover, there was a striking increase of activated CD152⁺ cells among CD3⁺CD56⁺ NKT cells in the liver of SR ( P  = 0.041).
Conclusion:  These findings demonstrate that sustained response to IFN/RBV treatment for patients with CHC is closely associated with increased dynamism of NK and NKT cells in the liver.     

Peripheral killer cells do not differentiate between asthma patients with or without fixed airway obstruction

Objective: The three main types of killer cells – CD8⁺ T cells, NK cells and NKT cells – have been linked to asthma and chronic obstructive pulmonary disease (COPD). However, their role in a small subset of asthma patients displaying fixed airway obstruction (FAO), similar to that seen in COPD, has not been explored. The objective of the present study was to investigate killer cell numbers, phenotype and function in peripheral blood from asthma patients with FAO, asthma patients without FAO, and healthy individuals. Methods: Peripheral CD8⁺ T cells (CD8⁺CD3⁺CD56^?), NK cells (CD56⁺CD3^?) and NKT-like cells (CD56⁺CD3⁺) of 14 asthma patients with FAO (post-bronchodilator FEV/FVC <0.7, despite clinician-optimised treatment), 7 asthma patients without FAO (post-bronchodilator FEV/FVC ≥ 0.7), and 9 healthy individuals were studied. Results: No significant differences were seen between the number, receptor expression, MAPK signalling molecule expression, cytotoxic mediator expression, and functional cytotoxicity of peripheral killer cells from asthma patients with FAO, asthma patients without FAO and healthy individuals. Conclusions: Peripheral killer cell numbers or functions do not differentiate between asthma patients with or without fixed airway obstruction.     

Circulating CD56dim natural killer cells and CD56+ T cells that produce interferon‐γ or interleukin‐10 are expanded in asymptomatic,E antigen‐negative patients with persistent hepatitis B virus infection

Infection with hepatitis B virus (HBV) can result in spontaneous resolution or chronic infection, which can remain asymptomatic or can progress to cirrhosis and/or hepatocellular carcinoma. The host immune response is thought to be a major determinant of the outcome of HBV infection and virus‐specific cytotoxic T lymphocytes (CTL) can mediate immunity against the virus and cause liver pathology. Antigen‐nonspecific innate lymphocytes may also contribute to HBV infection and liver disease, therefore, we examined the frequencies, phenotypes, cytolytic activities and cytokine profiles of circulating natural killer (NK) cells, CD1d‐restricted invariant natural killer T (iNKT) cells and CD56⁺ T cells in 102 asymptomatic HBV‐infected patients and compared them with those in 66 uninfected control subjects. NK cells expressing low levels of CD56 (CD56^dim) and CD56⁺ T cells were significantly expanded in the circulation of HBV‐infected patients compared with control subjects. CD1d expression and iNKT cell frequencies were similar in both groups. Despite these expansions, we did not detect augmented natural or cytokine‐induced cytotoxicity in the HBV‐infected subjects. All lymphocyte populations studied produced interferon‐γ (IFN‐γ) significantly more frequently when taken from HBV‐infected patients compared with when taken from healthy controls. Additionally, NK cells from the patients more frequently produced interleukin‐10. As our HBV‐infected cohort consisted of asymptomatic patients with low viral loads, we propose that CD56^dim NK cells and CD56⁺ T cells control HBV infection by noncytolytic mechanisms.     

Pathogenic role of natural killer T and natural killer cells in acetaminophen-induced liver injury in mice is dependent on the presence of dimethyl sulfoxide

Dimethyl sulfoxide (DMSO) is commonly used in biological studies to dissolve drugs and enzyme inhibitors with low solubility. Although DMSO is generally thought of as being relatively inert, it can induce biological effects that are often overlooked. An example that highlights this potential problem is found in a recent report demonstrating a pathogenic role for natural killer T (NKT) and natural killer (NK) cells in acetaminophen-induced liver injury (AILI) in C57Bl/6 mice in which DMSO was used to facilitate acetaminophen (APAP) dissolution. We report that NKT and NK cells do not play a pathologic role in AILI in C57Bl/6 mice in the absence of DMSO. Although AILI was significantly attenuated in mice depleted of NKT and NK cells prior to APAP treatment in the presence of DMSO, no such effect was observed when APAP was dissolved in saline. Because of this unexpected finding, the effects of DMSO on hepatic NKT and NK cells were subsequently investigated. When given alone, DMSO activated hepatic NKT and NK cells in vivo as evidenced by increased NKT cell numbers and higher intracellular levels of the cytotoxic effector molecules interferon-gamma (IFN-gamma) and granzyme B in both cell types. Similarly, when used as a solvent for APAP, DMSO again increased NKT cell numbers and induced IFN-gamma and granzyme B expression in both cell types. CONCLUSION: These data demonstrate a previously unappreciated effect of DMSO on hepatic NKT and NK cells, suggesting that DMSO should be used cautiously in experiments involving these cells.     

Role of cytolytic impairment of natural killer and natural killer T-cell populations in rheumatoid arthritis

Innate immunity has been widely accepted as one of the major cause for the alteration of immune system and progression of autoimmune diseases. Natural killer (NK) cells and natural killer T (NKT) cells have not been explored in clinical studies for their cytolytic components in association with rheumatoid arthritis (RA). The literature available for these potential candidates is controversial in terms of their protective or pathogenic role in disease severity of RA. Present study explained the role of NK and NKT cell populations and intracellular expression of caspases, perforin, granzymes A and B in the pathogenesis of RA in patients. DAS28 score was measured as the disease severity. Immunochemical parameters were studied by using monoclonal antibodies (mAbs) against different cell types in flow cytometry. Results indicated that that whatsoever is the change in percentage cell populations, ratio of NK and NKT cell populations always remained poised even in the disease state. Reactive oxygen species (ROS) levels were elevated with increased intracellular active caspase-3, perforin and granzyme expression in RA patients. Their elevated expressions were positively correlated with DAS28 suggesting the pathogenic role in RA. The expressions of pro-inflammatory cytokines were enhanced while the anti-inflammatory cytokine expressions were diminished in the patients. Present study may point towards futuristic therapeutic targets which can fascinate the pharmaceutical industries to selectively target these molecules in designing the therapeutic strategy of RA patients.     

Hepatic natural killer and natural killer T cells markedly decreased in two cases of drug-induced fulminant hepatic failure rescued by living donor liver transplantation

The human liver contains significant numbers of innate immune cells, such as natural killer (NK) cells and natural killer T (NKT) cells, which express both T-cell receptors and NK-cell receptors simultaneously. It has been suggested that the innate immune system plays a crucial role in the liver. In this report, the distribution of NK and NKT cells in the liver and peripheral blood of two patients with drug-induced fulminant hepatic failure (FHF) who had undergone living donor liver transplantation was examined. In both the liver and peripheral blood, the proportions of NK and NKT cells markedly decreased compared with those in healthy donors. It was also revealed that, unlike murine NKT cells, human CD56(+) T cells and CD57(+) T cells did not constitutively express CD28, which is one of the important costimulatory molecules on T cells. Additionally, the residual CD56(+) T cells and CD57(+) T cells in the patients expressed more CD28 than in controls. This result suggests that NKT cells might be more activated in FHF. Although the accumulation of further cases is required, it is suggested that both NK and NKT cells might be involved in hepatic injury in FHF.     

Altered expression and function of hepatic natural killer T cells in obese and diabetic KK‐Ay mice

Aim: To evaluate the role of natural killer (NK)T cells in the pathogenesis of non‐alcoholic steatohepatitis (NASH), here we investigated the expression and function of hepatic NKT cells in KK‐A^y mice, an animal model of metabolic syndrome. Methods: Male, 8‐week‐old KK‐A^y and C57Bl/6 mice were fed a high‐fat (HF) diet for 4 weeks. Some mice were given daily intragastric injections of pioglitazone for 5 days prior to or after dietary treatment. Results: In untreated KK‐A^y mice, the percentages of NKT cells in liver mononucleolar cells were nearly one‐third of those in C57Bl/6 controls. Elevations in interleukin (IL)‐4 and interferon (IFN)‐γ mRNA in the liver after a single injection of α‐galactosylceramide (GalCer) were blunted in KK‐A^y mice largely. Percentages of NKT cells, as well as GalCer‐induced increases in IL‐4 mRNA, were blunted significantly in both strains after HF diet feeding for 4 weeks. Interestingly, KK‐A^y mice pretreated with pioglitazone showed significant increases in NKT cell proportion, and GalCer‐induced increases in IL‐4 and IFN‐γ mRNA were also enhanced by pioglitazone. In KK‐A^y mice, the percentages of annexin V positive NKT cells were nearly 2.5‐fold higher than those in C57Bl/6 controls; however, pioglitazone decreased annexin V positive cells significantly. Moreover, pioglitazone increased NKT cell fraction in KK‐A^y mice even after HF diet feeding. Conclusion: KK‐A^y mice exhibit proportional and functional alterations in hepatic NKT cells in close relation with the development of steatohepatitis, and it is postulated that pioglitazone improves steatohepatitis in part through restoration of hepatic NKT cells.     

CD38 triggers cytotoxic responses in activated human natural killer cells

Receptors used by natural killer (NK) cells to mediate natural cytotoxicity are poorly defined, although it is now clear that a number of adhesion molecules can serve this function. CD38 transduces signals on T- and B-cell lines, and we asked whether it could trigger lytic and secretory responses in human NK cells. By using an anti-CD38 monoclonal antibody in reverse antibody-dependent cellular cytotoxicity experiments, it is shown that CD38 engagement triggers cytotoxic responses by activated NK cells, but not by cytotoxic T lymphocytes or fresh NK cells. Cross-linking with anti-CD38 F(ab')(2) caused activated NK cells to release granzymes and cytokines, but did not trigger an increase in intracellular Ca(2+). Fresh NK cells acquired CD38-dependent lytic function during activation with interleukin-2 (IL-2), and inhibitor studies suggested that IL-2 stimulated the de novo expression of proteins that act between CD38 and the lytic machinery in NK cells. The induction of proteins that link commonly expressed adhesion molecules to effector mechanisms could provide a paradigm for pathogen recognition by the innate immune system.     

Natural killer T cell deficiency in active adult‐onset Still's disease: Correlation of deficiency of natural killer T cells with dysfunction of natural killer cells

Objective

To examine the levels and functions of natural killer (NK) and natural killer T (NKT) cells, investigate relationships between NK and NKT cells, and determine the clinical relevance of NKT cell levels in patients with adult‐onset Still's disease (AOSD).

Methods

Patients with active untreated AOSD (n = 20) and age‐ and sex‐matched healthy controls (n = 20) were studied. NK and NKT cell levels were measured by flow cytometry. Peripheral blood mononuclear cells were cultured in vitro with α‐galactosylceramide (αGalCer). NK cytotoxicity against K562 cells and proliferation indices of NKT cells were estimated by flow cytometry.

Results

Percentages and absolute numbers of NKT cells were significantly lower in the peripheral blood of AOSD patients than in that of healthy controls. Proliferative responses of NKT cells to αGalCer were also lower in patients, and this was found to be due to proinflammatory cytokines and NKT cell apoptosis. In addition, NK cytotoxicity was found to be significantly lower in patients than in healthy controls, but NK cell levels were comparable in the 2 groups. Notably, this NKT cell deficiency was found to be correlated with NK cell dysfunction and to reflect active disease status. Furthermore, αGalCer‐mediated NK cytotoxicity, showing the interaction between NK and NKT cells, was significantly lower in AOSD patients than in healthy controls.

Conclusion

These findings demonstrate that NK and NKT cell functions are defective in AOSD patients and suggest that these abnormalities contribute to innate immune dysfunction in AOSD.

     

肝脏自然杀伤细胞在小鼠急性肝衰竭中的作用

目的 探讨肝脏自然杀伤(NK)细胞在3型鼠肝炎病毒(MHV-3)诱导的小鼠急性肝衰竭中的作用.方法 取6～8周龄雌性Balb/cJ小鼠,腹腔注射100 pfu MHV-3,采用流式细胞术检测感染MHV-3 0、24、48、70 h后的Balb/cJ小鼠肝脏、脾脏、外周血和骨髓中NK细胞的百分率及肝脏NK细胞表面活化分子CD69表达的百分率.细胞内细胞因子染色法检测肝脏NK细胞分泌干扰素γ的水平.非放射性细胞毒试验检测肝脏NK细胞的杀伤活性. 结果Balb/cJ小鼠感染MHV-3后,肝脏NK细胞的比例显著升高,在感染48 h后达到峰值(43.9%±2.3%),约为感染前的4倍,随后仍维持在较高水平至小鼠死亡;外周血NK细胞比例同样明显升高,在感染48 h后达到峰值(18.0%±5.4%),但随后显著同落,至70 h仅为1.3%±0.6%,脾脏和骨髓NK细胞比例均先明显减少后又有所上升.肝脏NK细胞在MHV-3感染48 h后其表面活化分子CD69表达明显上调,杀伤活性显著增强,同时分泌干扰素Y的水平也显著增加. 结论 Balb/cJ小鼠感染MHV-3后,来自骨髓和脾脏的NK细胞在肝脏迅速大量募集和活化,且杀伤活性显著增强,分泌干扰素Y水平也显著增加,表明肝脏NK细胞在MHV-3导致的急性肝衰竭中可能发挥着关键作用.     

Natural killer cells in highly exposed hepatitis C‐seronegative injecting drug users

Injecting drug use remains the major risk factor for hepatitis C (HCV) transmission. A minority of long‐term injecting drug users remain seronegative and aviraemic, despite prolonged exposure to HCV – termed highly exposed seronegative subjects. Natural killer (NK) cells have been implicated in this apparent protection. A longitudinal nested, three group case–control series of subjects was selected from a prospective cohort of seronegative injecting drug users who became incident cases (n = 11), remained seronegative (n = 11) or reported transient high‐risk behaviour and remained uninfected (n = 11). The groups were matched by age, sex and initial risk behaviour characteristics. Stored peripheral blood mononuclear cells were assayed in multicolour flow cytometry to enumerate natural killer cell subpopulations and to assess functional activity using Toll‐like receptor ligands before measurement of activation, cytokine production and natural cytotoxicity receptor expression. Principal components were derived to describe the detailed phenotypic characteristics of the major NK subpopulations (based on CD56 and CD16 co‐expression), before logistic regression analysis to identify associations with exposed, seronegative individuals. The CD56^dimCD16⁺ (P = 0.05, OR 6.92) and CD56^dimCD16^? (P = 0.05, OR 6.07) principal components differed between exposed, seronegative individuals and pre‐infection samples of the other two groups. These included CD56^dimCD16⁺ and CD56^dimCD16^? subsets with CD56^dimCD16⁺ IFN‐γ and TNF‐α on unstimulated cells, and CD56^dimCD16^? CD69⁺, CD107a⁺, IFN‐γ and TNF‐α following TLR stimulation. The cytotoxic CD56^dim NK subset thus distinguished highly exposed, seronegative subjects, suggesting NK cytotoxicity may contribute to protection from HCV acquisition. Further investigation of the determinants of this association and prospective assessment of protection against HCV infection are warranted.     

Suppressed natural killer cell activity in patients with chronic autoimmune thrombocytopenic purpura

Natural killer (NK) cell activity was studied in 17 patients with primary chronic idiopathic autoimmune thrombocytopenic purpura (ATP). Fifteen of 17 patients had a significantly reduced NK cytotoxicity against 51chromium labeled K562 target cells (mean LU20% = 18 +/- 20 in patients versus 65 +/- 25 in controls, P less than 0.001). NK activity was also significantly reduced in all of six patients with secondary ATP as compared with normal controls (LU20% 28 +/- 15, respectively, P less than 0.005). The NK activity in both patient groups correlated with the duration of therapy being received (r = 0.60, P less than 0.001). Immunophenotypic analysis of peripheral blood mononuclear cells from patients with ATP revealed that CD8- cells bearing CD57 (HNK-1, Leu 7) and CD3- cells bearing CD56 (Leu 19) were quantitatively within the normal range. These findings indicate that patients with ATP have a functional defect in NK cytolytic activity.     

Expansion and enhanced survival of natural killer cells expressing the killer immunoglobulin‐like receptor KIR3DL2 in spondylarthritis

Objective

The spondylarthritides (SpA) are strongly associated with possession of HLA–B27. We hypothesized that the expression of abnormal forms of HLA–B27 in SpA may have a pathogenic role through interaction with cells bearing natural killer (NK) receptors, in particular, killer immunoglobulin‐like receptor (KIR) KIR3DL2, a receptor for HLA–B27 homodimer (B27₂). We therefore undertook the present study to determine the number and function of NK and T cells bearing KIR3DL2 in SpA.

Methods

Expression of KIR3DL2 on NK and T cells was quantified in peripheral blood (PB) from 35 patients with SpA and 5 patients with juvenile enthesitis‐related arthritis (juvenile ERA); samples were compared with samples from healthy and rheumatoid arthritis (RA) controls. Paired synovial fluid (SF) was studied where available. Expression of other KIRs as well as activation, memory, and homing markers on KIR3DL2+ NK and T cells was quantified. NK cell survival was assessed using the apoptotic markers annexin V and 7‐aminoactinomycin D, and cytotoxicity by ⁵¹Cr release assay.

Results

In SpA, an increased number of PB and SF NK and CD4+ T cells expressed the KIR3DL2 receptor compared with controls. In ERA, KIR3DL2 expression was increased in PB and SF CD4 T cells (and SF NK cells) compared with RA controls. KIR3DL2+ NK cells had an activated phenotype, and were protected from apoptosis by culture with a cell line expressing B27₂. SpA PB mononuclear NK cells from SpA patients showed greater cytotoxicity than those from controls.

Conclusion

KIR3DL2 expression on NK cells and CD4 lymphocytes is increased in SpA and ERA. These cells are activated and may have a pathogenic role.

     

Enhanced natural killer cell activity is found in exposed uninfected recipients of hepatitis C‐contaminated blood

A minority of injecting drug users, termed exposed uninfected, are resistant to hepatitis C (HCV) infection despite repeated low‐dose exposures. We identify for the first time a cohort of blood recipients who remained uninfected despite large‐dose exposure to HCV‐contaminated blood and characterize immune factors that may confer protection. Of 1340 blood recipients from the English Look Back database who were transfused HCV‐contaminated blood, we identified 8 who remained uninfected. In these 8 exposed uninfecteds, we characterized their natural killer (NK) cell populations and HCV‐specific T‐cell responses. Findings were compared with 10 spontaneous resolvers of HCV infection, 10 patients with chronic HCV infection and 10 healthy controls. Exposed uninfecteds had significantly greater numbers of NK cells with the activating receptor NKp30+ on CD56^bright and CD56^dim subsets compared with other groups (P < .05). Following interleukin‐2 activation, NK cells of exposed uninfecteds had enhanced cytotoxicity that positively correlated with NKp30 expression (P = .02). Differences in NKp80 and KIR2DL3 expression were also observed. HCV‐specific T‐cell responses were observed in some exposed uninfecteds but of low amplitude. Exposure without infection following transfusion of HCV‐contaminated blood is a very rare phenomenon and suggests a high level of resistance to infection. Enhanced NK cell activation and killing, with weak HCV‐specific T‐cell responses, were observed many years after exposure in uninfected recipients and may contribute to protection from HCV acquisition, although additional protective factors are being sought in this important cohort.     

Invariant natural killer T cells in chronic obstructive pulmonary disease

Background and objective: Invariant natural killer T (iNKT) cells may play an important role in regulating the innate and acquired immune systems in chronic obstructive pulmonary disease (COPD). However, there is little information regarding the potential role of iNKT cells in the pathogenesis of COPD. To investigate whether iNKT cells have an important role in COPD, the frequency of iNKT cells in peripheral blood of patients with COPD was analysed. Methods: This was a comparative study of 28 patients with COPD and 19 age‐matched healthy control subjects. Blood iNKT cells were stained with 6B11 mAb, anti‐T cell receptor Vα24 mAb, anti‐T cell receptor Vβ11 mAb or α‐galactosylceramide‐loaded CD1d‐tetramer, and analysed by flow cytometry. Results: The frequency of CD4⁺ 6B11⁺ iNKT, CD4⁺ Vα24⁺ iNKT, CD4⁺ Vβ11⁺ iNKT and CD3⁺ 6B11⁺ iNKT cells was significantly lower in peripheral blood of patients with COPD than in that of healthy control subjects. The frequency of CD4⁺ 6B11⁺ iNKT cells was significantly lower in patients with exacerbations of COPD compared with those with stable COPD. Conclusions: The frequency of iNKT was decreased in peripheral blood of patients with COPD. These results strongly suggest that iNKT cells may play an important role in the pathogenesis of COPD.     

The immune response to primary EBV infection: a role for natural killer cells

The role of antigen-specific CD3(+)CD8(+) cytotoxic T cells in the control of primary Epstein-Barr Virus (EBV) infection is well established. However, time is required for the antigen-specific immune response to develop and expand. In contrast, innate immune responses, such as natural killer (NK) cells, are considered vital early in the infection process. We analysed the scale, phenotype and function of the NK cell response during symptomatic primary EBV infection, infectious mononucleosis (IM) and showed that NK cell numbers were significantly elevated both at diagnosis of IM and in the first month following diagnosis. There were also significant changes in cell phenotype and function, an increase in the proportion of CD56(bright) cells at diagnosis, and freshly isolated cells showing an enhanced ability to kill EBV-infected cell lines. Moreover, in our cohort of IM patients higher NK cell counts were associated with significantly lower viral load in peripheral blood. Our results suggest NK cells have an important role in the control of primary EBV infection by eliminating infected B cells and augmenting the antigen-specific T cell response via release of immunomodulatory cytokines. The magnitude of the NK cell response may ultimately determine whether primary EBV infection has a clinical outcome.