Regulation of experimental autoimmune encephalomyelitis by natural killer (NK) cells

Regulatory NK-cell functions in inflammation and autoimmunity

Natural killer (NK) cells were viewed traditionally as cytotoxic effector cells whose rapid killing of infected and transformed cells without preactivation provides a first line of defense prior to the initiation of an adaptive immune response against infection and tumor development. However, it has become clear that NK cells interact with various components of the immune system, and therefore have the potential to function as regulatory cells. While NK cells can assist in dendritic cell (DC) maturation and T-cell polarization, increasing evidence indicates that NK cells can also prevent and limit adaptive (auto) immune responses via killing of autologous myeloid and lymphoid cells. Investigating immunoregulatory NK-cell functions might generate exciting insights into the reciprocal regulation between NK-cell-mediated innate immunity and adaptive immune responses, improve our capacity to monitor these cells as surrogate markers for disease activity and treatment responses in autoimmune diseases, and, perhaps, provide new prospects for NK cell-directed therapies.

Myelin basic protein-reactive T cells persist in an inactive state in the bone marrow of Lewis rats that have recovered from autoimmune encephalomyelitis

Lewis rats immunized with guinea pig myelin basic protein residues 68-86 develop acute experimental autoimmune encephalomyelitis and recover. The predominant T cell receptor expressed by the encephalitogenic T cells is TCRBV8S2. They persist in bone marrow many weeks after recovery. CD3 is down-regulated, but >90% express CD4. They fail to proliferate to GPMBP68-86 unless a nitric oxide synthase inhibitor is added to the cultures. Perhaps these are memory T cells that are maintained in a suppressed state in BM by a nitric oxide-dependent mechanism.

A significantly impaired natural killer cell activity due to a low activity on a per-cell basis in rheumatoid arthritis

To elucidate the characterization of peripheral natural killer (NK) cells in patients with rheumatoid arthritis (RA), we investigated the NK cell activity, the expression of NK cell activating receptors and intracellular molecules. The NK activity was analyzed in 27 RA patients, 22 primary Sjögren's syndrome (SS) patients, and 15 healthy individuals using the (51)Chrominium release assay. The expression of NK cell activating receptors (NKG2D, CD244, CD2, and CD16) and intracellular molecules (granzyme B, perforin, and TCR zeta chain) in CD3-CD56+ cells were characterized by flow cytometry. The serum cytokine levels (IL-6, TNFalpha, and IL-18) were measured using ELISA. Both the NK cell activity and the activity on a per-cell basis were observed to significantly decrease in the RA patients in comparison to the controls. The expression of NKG2D and CD244 also significantly decreased in both the RA and primary SS patients, whereas the significant decrease in the CD16 expression was only observed in the RA patients. The titer of the serum IL-6, TNFalpha, and IL-18 was significantly higher in the RA patients than in the controls. These data suggest that a low NK activity on a per-cell basis might therefore contribute to an impaired NK activity in the patients with RA.

Human NK cells kill resting but not activated microglia via NKG2D- and NKp46-mediated recognition

Microglia are resident macrophage-like APCs of the CNS. To avoid escalation of inflammatory processes and bystander damage within the CNS, microglia-driven inflammatory responses need to be tightly regulated and both spatially and temporally restricted. Following traumatic, infectious, and autoimmune-mediated brain injury, NK cells have been found in the CNS, but the functional significance of NK cell recruitment and their mechanisms of action during brain inflammation are not well understood. In this study, we investigated whether and by which mechanisms human NK cells might edit resting and activated human microglial cells via killing in vitro. IL-2-activated NK cells efficiently killed both resting allogeneic and autologous microglia in a cell-contact-dependent manner. Activated NK cells rapidly formed synapses with human microglial cells in which perforin had been polarized to the cellular interface. Ab-mediated NKG2D and NKp46 blockade completely prevented the killing of human microglia by activated NK cells. Up-regulation of MHC class I surface expression by TLR4 stimulation protected microglia from NK cell-mediated killing, whereas MHC class I blockade enhanced cytotoxic NK cell activity. These data suggest that brain-infiltrating NK cells might restrict innate and adaptive immune responses within the human CNS via elimination of resting microglia.

Killers and beyond: NK-cell-mediated control of immune responses

Effective immunity requires coordinated activation of innate and adaptive immune responses. NK cells are principal mediators of innate immunity, able to respond to challenge quickly and generally without prior activation. The most acknowledged functions of NK cells are their cytotoxic potential and their ability to release large amounts of cytokines, especially IFN-gamma. Recently, it has become clear that NK cells are more than assassins. Indeed, NK cells play critical roles in shaping adaptive immunity.

Role of NK cells and invariant NKT cells in multiple sclerosis

Natural killer (NK) cells and invariant natural killer T (iNKT) cells are two distinctive lymphocyte populations, each possessing its own unique features. Although NK cells are innate lymphocytes with cytotoxic property, they play an immunoregulatory role in the pathogenesis of autoimmune diseases. NKT cells are T cells expressing invariant TCR a-chains, which are known to bridge innate and adaptive arms of the immune system. Accumulating data now support active involvement of these cells in multiple sclerosis (MS). However, unlike professionally committed regulatory cells such as Foxp3(+) regulatory T cells, NK, and iNKT cells have dual potential of acting as either protective or pathogenic lymphocytes depending on the disease setting, adding complexity to the interpretation of data obtained from human and rodent studies. They are potential therapeutic targets in MS, and further in-depth understanding of these cells will lead to designing new strategies to overcome the disabling disease MS.

Animal models of multiple sclerosis

Since its first description, experimental autoimmune encephalomyelitis, originally designated experimental allergic encephalitis (EAE), has been proposed as animal model to investigate pathogenetic hypotheses and test new treatments in the field of central nervous system inflammation and demyelination, which has become, in the last 30 years, the most popular animal model of multiple sclerosis (MS). This experimental disease can be obtained in all mammals tested so far, including nonhuman primates, allowing very advanced preclinical studies. Its appropriate use has led to the development of the most recent treatments approved for MS, also demonstrating its predictive value when properly handled. Some of the most exciting experiments validating the use of neural precursor cells (NPCs) as a potential therapeutic option in CNS inflammation have been performed in this model. We review here the most relevant immunological features of EAE in the different animal species and strains, and describe detailed protocols to obtain the three most common clinical courses of EAE in mice, with the hope to provide both cultural and practical basis for the use of this fascinating animal model.

Splenic natural killer cell activity in two models of experimental neurodegenerative diseases

Natural killer (NK) cells are antitumour/anti-viral effectors and play important roles in shaping the immune system, but their role in neurodegenerative diseases is not clear. Here, we investigated the fate of these cells in two neurodegenerative diseases. In the first model, the activity of NK cells was examined in mice with experimental autoimmune encephalomyelitis (EAE) treated with glatiramer acetate (GA or Copaxone), a drug used to treat EAE in animals and multiple sclerosis in human. The second disease model is twitcher (Galc(twi)/Galc(twi)) mice, which represents an authentic model of human Krabbe's disease. Administration of GA ameliorated EAE in SJL mice corroborated with isolating NK cells that expressed higher killing than cells isolated from vehicle-dosed animals against immature or mature dendritic cells (DCs). However, this drug showed no effect on the numbers of NK cells or the expression of CD69 molecule. On the other hand, NK cells either disappeared from the spleens or were present in low numbers in the white pulp areas of Galc(twi)/Galc(twi) mice, which have increased D-galactosyl-beta1-1'-sphingosine (GalSph) levels. Analysis by confocal microscopy shows that NK cells found in the spleens of Galc(twi)/Galc(twi) mice were apoptotic. Incubating NK cells in vitro with GalSph induced the apoptosis in these cells, confirming the results of twitcher mice. Our results provide the first evidence showing that amelioration of EAE in mice is corroborated with NK cell lysis of antigen-presenting DCs, whereas NK cell distribution into the spleen is altered in a devastating lipid disorder corroborated with induction of their apoptosis.

Splenic natural killer cell activity in two models of experimental neurodegenerative diseases

Natural killer (NK) cells are antitumour/anti-viral effectors and play important roles in shaping the immune system, but their role in neurodegenerative diseases is not clear. Here, we investigated the fate of these cells in two neurodegenerative diseases. In the first model, the activity of NK cells was examined in mice with experimental autoimmune encephalomyelitis (EAE) treated with glatiramer acetate (GA or Copaxone), a drug used to treat EAE in animals and multiple sclerosis in human. The second disease model is twitcher (Galc(twi)/Galc(twi)) mice, which represents an authentic model of human Krabbe's disease. Administration of GA ameliorated EAE in SJL mice corroborated with isolating NK cells that expressed higher killing than cells isolated from vehicle-dosed animals against immature or mature dendritic cells (DCs). However, this drug showed no effect on the numbers of NK cells or the expression of CD69 molecule. On the other hand, NK cells either disappeared from the spleens or were present in low numbers in the white pulp areas of Galc(twi)/Galc(twi) mice, which have increased D-galactosyl-beta1-1'-sphingosine (GalSph) levels. Analysis by confocal microscopy shows that NK cells found in the spleens of Galc(twi)/Galc(twi) mice were apoptotic. Incubating NK cells in vitro with GalSph induced the apoptosis in these cells, confirming the results of twitcher mice. Our results provide the first evidence showing that amelioration of EAE in mice is corroborated with NK cell lysis of antigen-presenting DCs, whereas NK cell distribution into the spleen is altered in a devastating lipid disorder corroborated with induction of their apoptosis.

Posttranscriptional regulation of II10 gene expression allows natural killer cells to express immunoregulatory function

Natural killer (NK) cells play a well-recognized role in early pathogen containment and in shaping acquired cell-mediated immunity. However, indirect evidence in humans and experimental models has suggested that NK cells also play negative regulatory roles during chronic disease. To formally test this hypothesis, we employed a well-defined experimental model of visceral leishmaniasis. Our data demonstrated that NKp46(+)CD49b(+)CD3(-) NK cells were recruited to the spleen and into hepatic granulomas, where they inhibited host protective immunity in an interleukin-10 (IL-10)-dependent manner. Although IL-10 mRNA could be detected in activated NK cells 24 hr after infection, the inhibitory function of NK cells was only acquired later during infection, coincident with increased IL-10 mRNA stability and an enhanced capacity to secrete IL-10 protein. Our data support a growing body of literature that implicates NK cells as negative regulators of cell-mediated immunity and suggest that NK cells, like CD4(+) T helper 1 cells, may acquire immunoregulatory functions as a consequence of extensive activation.

Invariant NKT cells regulate experimental autoimmune encephalomyelitis and infiltrate the central nervous system in a CD1d-independent manner

Invariant NKT cells are CD1d-restricted T cells specific for glycolipid Ags. Their activation or transgenic enrichment abrogates the development of experimental autoimmune encephalomyelitis (EAE). Herein, we demonstrate that in NKT-enriched mice the protection from EAE is associated with the infiltration of NKT cells in the CNS and the local expression of CD1d. This indicates that the CNS acquires the potential for local glycolipid presentation when exposed to inflammatory stress, permitting the triggering of NKT cells. To address the importance of CD1d-mediated Ag presentation, we used transgenic mice that express CD1d solely in the thymus. Interestingly, enrichment of NKT cells in these mice also conferred resistance to EAE, with an efficacy indistinguishable from that of NKT-enriched CD1d-sufficient mice. This protection was due to an abrogation of the encephalitogenic Th1 and Th17 response in the spleen, revealing that endogenous glycolipid presentation is dispensable for the regulatory function of NKT cells in EAE. Moreover, abrogating extrathymic CD1d expression failed to affect both the recruitment of NKT cells and their effector phenotype. CNS-infiltrating NKT cells were characterized by a cytotoxic IFN-gamma(high)IL-4(low)IL-10(low)granzyme B(high) profile, irrespective of the local expression of CD1d. Glycolipid Ag presentation is therefore dispensable for the control of autoimmune demyelination by NKT cells, underlining the importance of alternative cognate and/or soluble factors in the control of NKT cell function.

T-cells expressing natural killer (NK) receptors are altered in multiple sclerosis and responses to alpha-galactosylceramide are impaired

Multiple sclerosis (MS) is an autoimmune disorder characterised by clinical relapse and remission and pathological demyelination with varying inflammation. Because it is suggested that T-cells expressing natural killer cell receptors (NKR) play important roles in regulating human autoimmune diseases, we have quantified populations of T-cells expressing the NKR CD56, CD161 and CD94 in the peripheral blood of MS patients, in healthy control subjects (HS) and in patients with other neurological diseases (OND). CD161(+) T-cells and CD94(+) T-cells were significantly decreased in MS patients with primary progressive disease and secondary progressive disease respectively whereas CD56(+) T-cell numbers were unchanged. In contrast NKT-cells that express the invariant Valpha24-Jalpha18(+) T-cell receptor identified here by specific receptor antibody and CD1d-tetrameric PBS57-loaded complexes, were increased in MS patients compared with HS. Reductions in CD161(+) T-cells and CD94(+) T-cells relative to HS were also observed in the OND group and this was particularly prominent in Parkinsonian patients. A striking functional finding was that while NKT-cells in unfractionated peripheral blood from healthy subjects expanded in number and produced IFN-gamma upon stimulation with alpha-galactosylceramide, NKT-cells from MS patients did not. Thus we have identified alterations in a number of potentially important lymphocyte sub-populations warranting further investigation in the immune response in MS.

Lipoic acid stimulates cAMP production via the EP2 and EP4 prostanoid receptors and inhibits IFN gamma synthesis and cellular cytotoxicity in NK cells

The antioxidant lipoic acid (LA) treats and prevents the animal model of multiple sclerosis (MS), experimental autoimmune encephalomyelitis (EAE). In an effort to understand the therapeutic potential of LA in MS, we sought to define the cellular mechanisms that mediate the effects of LA on human natural killer (NK) cells, which are important in innate immunity as the first line of defense against invading pathogens and tumor cells. We discovered that LA stimulates cAMP production in NK cells in a dose-dependent manner. Studies using pharmacological inhibitors and receptor transfection experiments indicate that LA stimulates cAMP production via activation of the EP2 and EP4 prostanoid receptors and adenylyl cyclase. In addition, LA suppressed interleukin (IL)-12/IL-18 induced IFNgamma secretion and cytotoxicity in NK cells. These novel findings suggest that LA may inhibit NK cell function via the cAMP signaling pathway.

In vivo regulation of experimental autoimmune encephalomyelitis by NK cells: alteration of primary adaptive responses

Innate immune responses provide the host with its first line of defense against infections. Signals generated by subsets of lymphocytes, including NK cells, NKT cells, and APC during this early host response determine the nature of downstream adaptive immune responses. In the present study, we have examined the role of innate NK cells in an autoimmune model through the use of primary immunization with the myelin oligodendrocyte glycoprotein peptide to induce experimental autoimmune encephalomyelitis (EAE). Our studies have shown that in vivo depletion of NK cells can affect the adaptive immune responses, because NK cells were found to regulate the degree of clinical paralysis and to alter immune adaptive responses to the myelin oligodendrocyte glycoprotein peptide. The requirement for NK cells was reflected by changes in the T cell responses and diminished clinical disease seen in mice treated with anti-NK1.1, anti-asialo GM1, and selected Ly49 subtype-depleted mice. In addition to alteration in T cell responses, the maturational status of dendritic cells in lymph nodes was altered both quantitatively and qualitatively. Finally, examination of TCR Vbeta usage of the brain lymphocytes from EAE mice indicated a spectra-type change in receptor expression in NK- depleted mice as compared with non-NK-depleted EAE mice. These findings further establish a recently postulated link between NK cells and the generation of autoreactive T cells.

Regulatory T cells control dendritic cell/NK cell cross-talk in lymph nodes at the steady state by inhibiting CD4+ self-reactive T cells

The CD4(+)CD25(+)Foxp3(+) regulatory T cells (Treg) play an important role in the control of peripheral tolerance by directly inhibiting conventional T cell proliferative and effector functions. However, the mechanisms by which Treg regulate the homeostasis of lymph nodes remain unclear. In this study, we show in a mouse model that Treg control two major checkpoints dictated by the interaction between self-reactive CD4(+) T cells and resident dendritic cell (DC) in secondary lymphoid organs. First, Treg inhibit the production of CCR5 ligands, limiting the CCR5-dependent recruitment of DC in the lymph nodes. Second, Treg prevent the DC exposure of IL-15Ralpha, markedly interfering in the DC-mediated NK cell proliferation in vivo. Therefore, the DC/T cell autoreactivity leading to NK cell triggering could potentially be controlled by the coinhibition of both IL-15Ralpha and CCR5 in autoimmune disorders in which NK cells play a deleterious role.

Investigation of killer cell immunoglobulin-like receptor (KIR) gene diversity: KIR2DL2, KIR2DL5 and KIR2DS5

Human killer cell immunoglobulin-like receptor (KIR) genes are important for restraining natural killer cytotoxicity toward cells with autologous human leukocyte antigen (HLA) while targeting cells lacking or expressing low levels of self-HLA molecules. KIR gene content and alleles vary across individual genomes and populations, requiring specialized laboratory tools for their characterization. Here, we detail methods based on sequence-specific polymerase chain reaction amplification and oligonucleotide probe hybridization to identify alleles of KIR2DL2, KIR2DL5A, KIR2DL5B and KIR2DS5. Allele frequencies for a Northern Irish population of 354 individuals typed with this system are given, along with results from 132 cell lines from the International Histocompatibility Workshop that cover many world populations. This information complements published reports by our laboratory for allele-level typing of other KIR members, totaling 12 of the 17 known genes. These methods are allowing us to characterize KIR haplotypes in our population.

Treating multiple sclerosis with monoclonal antibodies

Therapeutic monoclonal antibodies (mAbs) are potent new tools for a molecular targeted approach to modify the course of multiple sclerosis (MS). Besides natalizumab, which was approved in 2006, three other mAbs (alemtuzumab, rituximab and daclizumab) were successfully tested in Phase II MS trials. In this review, introductory notes on the development and systematic nomenclature of therapeutic mAbs in general, set the stage for a detailed discussion of the four mAbs mentioned. We summarize non-MS indications, expression and function of target antigens, scientific rationales for MS therapy, putative modes of action and pharmacological aspects. Particularly, we provide a critical discussion of clinical MS trials, including protocols and interim analyses of trials currently underway. The natalizumab section pays special attention to the clinical handling of safety issues and the diagnostic use of neutralizing antibodies. We finally develop a scenario for how each of the four mAbs might evolve into the market of MS therapeutics within the coming years.

NK cells in autoimmunity: a two-edg'd weapon of the immune system

Natural killer (NK) cells are part of the innate-immune system and respond rapidly to a variety of insults via cytokine secretion and cytolytic activity. Their main function is first line of innate immunity across viral, bacterial and parasitic infections. NK-cells are not solely killers but can also act as regulators of adaptive immunity. It is evident from literature that NK-cells are deeply involved in autoimmunity, but the question is how and why they act as a two edged weapon. Number of circulating NK-cells can be frequently altered depending on the disease taken into consideration. Cytokine milieu, the microenvironment in which they mature and other stimuli acting on different cell surface receptors may differently trigger NK-cells response and influence their role in autoimmune diseases. Functional differences between NK-cells at different anatomical sites, the adaptability of NK-cells effector responses and genetic factors may also explain differences in such responses. Thus, NK-cell alterations may be associated with increased autoimmunity and the modulation in the number of circulating NK-cells seems to be a primary event rather than an active inflammation/drug administration consequence during inflammatory/autoimmune processes, playing a fundamental role in the pathogenesis of a number of autoimmune diseases.

Natural killer (NK) cells from killers to regulators: distinct features between peripheral blood and decidual NK cells

Natural killer (NK) cells are a key component of innate immunity, particularly crucial during the early phase of immune responses against certain viruses, parasites, and microbial pathogens. The role of NK cell during pregnancy has been vividly discussed over the past years and it is now becoming increasingly clear that NK cells control pregnancy maintenance at several levels. In normal pregnancy, it appears that they provide benefit by properly secreting cytokines, chemokines and angiogenic factors rather than functioning as cytotoxic effector cells. However, as they are endowed with all the cytolytic weapons, they promptly become capable of attacking fetal and maternal tissues during infection and inflammation.

Immunoregulatory factors in multiple sclerosis patients during and after pregnancy: relevance of natural killer cells

Multiple sclerosis (MS) ameliorates typically during pregnancy but after the delivery the relapse rate often increases. Our study was conducted to understand the immunoregulatory mechanisms accompanying this phenomenon. MS patients were followed-up prospectively during pregnancy and 6 months postpartum, with immunological characterization of the peripheral blood. Groups of age- and parity-matched healthy pregnant women, and age- and sex-matched non-pregnant women and non-pregnant MS patients were studied as controls. In our patient cohort, the annualized relapse rate was 1.0 +/- 1.0 relapses/woman/year (mean +/- standard deviation) during the year before pregnancy, but dropped to 0.2 +/- 0.9 during the third trimester (P = 0.02). After the delivery the relapse rate increased again to 1.4 +/- 1.9 (1-3 months postpartum versus third trimester P = 0.003). While percentages of peripheral blood CD3, CD4, CD8 and CD19 immune cell subsets were unchanged over the observation period, reduced disease activity during the last trimester was associated with a significant increase in the percentage of circulating CD56(bright) natural killer (NK) cells. Simultaneously, the proportion of circulating CD56(dim) NK cells was clearly reduced. No alteration was noted in CD4+ CD25(high) forkhead box P3+ regulatory T cells. Production of interferon-gamma by peripheral blood lymphocytes was down-regulated significantly during pregnancy in comparison to the postpartum period, resulting in an increased T helper type 2 (Th2) : Th1 ratio during pregnancy. In conclusion, pregnant state in MS patients is characterized by an increase in the percentage of CD56(bright) NK cells and by enhanced Th2 type cytokine secretion. Our findings suggest a potential role for CD56(bright) regulatory NK cells in the control of autoimmune inflammation during pregnancy in MS.

IL-21 receptor expression determines the temporal phases of experimental autoimmune encephalomyelitis

The IL-21 receptor (IL-21R) consists of a unique subunit and a common gamma chain (gamma(c)) that is shared with other cytokines including IL-2, IL-4, IL-7, and IL-15. The interaction between IL-21 and IL-21R results in significant effects on both innate and adaptive immune responses. In this study we examined the influence of IL-21R deficiency (IL-21R(-/-)) on the development of experimental autoimmune encephalomyelitis (EAE), an animal model of human multiple sclerosis (MS). IL-21R(-/-) mice developed EAE earlier and more severe neurological impairment than control mice, yet those mice could effectively recover from neurological deficits. The impact on EAE initiation by IL-21R deficiency was associated with a defect of CD4(+)CD25(+) T regulatory (Treg) cells and a down-regulated expression of Foxp3. The recovery from IL-21R(-/-) EAE was correlated with an expansion of Treg cells as well as an organ-specific redistribution of NK cells. These results suggest that a temporal influence of IL-21 on the activity of immunoregulatory circuits can be important in the modulation of the course of the autoimmune disease.

Role of natural killer cells in the pathogenesis and progression of multiple sclerosis

Natural killer (NK) cells are a subset of lymphocytes which have long been alleged to play an immunoregulatory role in the prevention of autoimmune diseases. Here, we briefly review NK cell features and the major findings from studies on NK cells in human and animals susceptible to multiple sclerosis (MS). Although most studies in human seem to suggest an association between disease and deficiencies in NK cells, it is also clear that NK cells can be both protective and pathogenic in MS models. These contrasting observations could result from differences in experimental procedures as well as from differences in NK cell subset targeted. Whatever the case, the functional features of these cells and their potential role in regulation of autoimmunity suggest that NK cell-based therapies might be an interesting approach for the treatment of multiple sclerosis.

EAE tolerance induction with Hsp70-peptide complexes depends on H60 and NKG2D activity

Inflammation leads to induction of tissue stress conditions that might contribute to the generation of mechanisms limiting ongoing immune responses. We have shown previously that peptides derived from brain tissue of mice with experimental autoimmune encephalomyelitis (EAE) complexed with the chaperone heat shock protein 70 (Hsp70-pc) induce an NK-cell-dependent tolerance for subsequent EAE sensitization. We now present data that showed that the MHC class I-related glycoprotein H60 determines Hsp70-pc-induced EAE inhibition. Hsp70-pc led to significant and selective up-regulation of H60 expression in SJL/J mice, and Ab-blocking of H60 expression led to loss of EAE tolerance. Similarly, blocking of the NK cell receptor for H60, NKG2D, also reversed the Hsp70-pc-induced EAE inhibition. In contrast, in C57BL/6 mice H60 was not expressed, and Hsp70-pc-induced tolerance was not detected. The NK cell mediated Hsp70-pc-induced tolerance to EAE was dependent on modulation of dendritic cells function leading to diminished T cell reactivity to PLP. As, no increase of H60 expression on T cells from EAE mice immunized with PLP was detected, and no enhanced loss of CD3+ H60+ over CD3+ H60- cells in Hsp70-pc-induced EAE tolerance was found direct killing of H60+ PLP-reactive cells seems not to be involved in the Hsp70-pc-induced tolerance induction. We have provided evidence that Hsp70-pc-induced tolerance for EAE, mediated by NK cells, involves induction of H60 ligand and its interaction with NKG2D receptor. NK cells tolerization of EAE depends on altered dendritic cells activity leading to enhanced death of Ag reactive cells.

The role of natural killer cells in curbing neuroinflammation

Natural killer (NK) cells are evolutionarily early lymphocytes that lack antigen-specific receptors and, hence, are considered to be part of the innate immune system. The majority of research on NK cells has focused on their ability to lyse "target cells", generally identified by low or absent MHC Class I expression, such as tumor cells and virus infected cells. However, an alternative role of these leukocytes as regulators of adaptive (and potentially destructive) immune responses, in particular organ-specific autoimmune diseases, has been increasingly recognized. Here we discuss the growing body of evidence that NK cells limit damage in autoimmune demyelinating disease by inhibiting autoreactive T cell responses without harming resident neurons or glia.

The Basic Immune Simulator: an agent-based model to study the interactions between innate and adaptive immunity

BACKGROUND

We introduce the Basic Immune Simulator (BIS), an agent-based model created to study the interactions between the cells of the innate and adaptive immune system. Innate immunity, the initial host response to a pathogen, generally precedes adaptive immunity, which generates immune memory for an antigen. The BIS simulates basic cell types, mediators and antibodies, and consists of three virtual spaces representing parenchymal tissue, secondary lymphoid tissue and the lymphatic/humoral circulation. The BIS includes a Graphical User Interface (GUI) to facilitate its use as an educational and research tool.

RESULTS

The BIS was used to qualitatively examine the innate and adaptive interactions of the immune response to a viral infection. Calibration was accomplished via a parameter sweep of initial agent population size, and comparison of simulation patterns to those reported in the basic science literature. The BIS demonstrated that the degree of the initial innate response was a crucial determinant for an appropriate adaptive response. Deficiency or excess in innate immunity resulted in excessive proliferation of adaptive immune cells. Deficiency in any of the immune system components increased the probability of failure to clear the simulated viral infection.

CONCLUSION

The behavior of the BIS matches both normal and pathological behavior patterns in a generic viral infection scenario. Thus, the BIS effectively translates mechanistic cellular and molecular knowledge regarding the innate and adaptive immune response and reproduces the immune system's complex behavioral patterns. The BIS can be used both as an educational tool to demonstrate the emergence of these patterns and as a research tool to systematically identify potential targets for more effective treatment strategies for diseases processes including hypersensitivity reactions (allergies, asthma), autoimmunity and cancer. We believe that the BIS can be a useful addition to the growing suite of in-silico platforms used as an adjunct to traditional research efforts.

NK1.1 Cells Downregulate Murine Endotoxin-Induced Uveitis Following Intraocular Administration of Interleukin-12

To evaluate the role of IFN-gamma (interferon gamma) in IL-12- (interleukin-12)-induced inhibition of the inflammatory response in the eye during endotoxin-induced uveitis (EIU). C57BL/6 wild type mice and IFN-gamma-deficient (GKO) mice were injected with 250 microg of Salmonella typhymurium endotoxin as a model for EIU. Animals were then injected intraocularly with 100 ng of rIL-12 or the equivalent volume of Phosphate-buffer saline (PBS). Histopathologic grading of disease was performed 12, 36 and 72 h after endotoxin injection. Chemokine mRNA expression in the eye was evaluated by reverse transcriptase-polymerase chain reaction. Depletion of NK1.1+ cells in vivo was performed using a PK136 antibody. Depletion of IFN-gamma was performed using the R4-6A2 antibody. C57BL/6 mice treated with rIL-12 intraocularly were protected from the development of EIU. Neutralization of IFN-gamma with a monoclonal antibody abrogated such protection. The IL-12 protective effects were lost in NK1.1-depleted mice. Intraocular IL-12 decreased the expression of keratinocyte-derived chemokines (KC) gene but had no effect on macrophage inflammatory protein (MIP-2) gene. The protective effect of IL-12 during EIU occurs through production of IFN-gamma by NK1.1+ cells. IL-12-induced higher levels of IFN-gamma are also correlated with lower expression of the chemokine KC, resulting in diminished attraction of neutrophils to the inflammatory site.

Regulation of activated CD4+ T cells by NK cells via the Qa-1-NKG2A inhibitory pathway

The ability of natural-killer cells to regulate adaptive immunity is not well understood. Here we define an interaction between the class Ib major histocompatibility complex (MHC) molecule Qa-1-Qdm on activated T cells responsible for adaptive immunity and CD94-NKG2A inhibitory receptors expressed by natural-killer cells by using Qa-1-deficient and Qa-1 knockin mice containing a point mutation that selectively abolishes Qa-1-Qdm binding to CD94-NKG2A receptors. The Qa-1-NKG2A interaction protected activated CD4+ T cells from lysis by a subset of NKG2A+ NK cells and was essential for T cell expansion and development of immunologic memory. Antibody-dependent blockade of this Qa-1-NKG2A interaction resulted in potent NK-dependent elimination of activated autoreactive T cells and amelioration of experimental autoimmune encephalomyelitis. These findings extend the functional reach of the NK system to include regulation of adaptive T cell responses and suggest a new clinical strategy for elimination of antigen-activated T cells in the context of autoimmune disease and transplantation.

Expansion of CD56Bright natural killer cells in the peripheral blood of multiple sclerosis patients treated with interferon-beta

We studied how interferon-beta (IFN-beta) treatment of relapsing-remitting multiple sclerosis (MS) affects subgroups of natural killer cells (NK cells). Following IFN-beta treatment, there was an expansion of CD56(Bright) NK-cells in the peripheral blood of MS patients, while at the same time the proportion of CD56(Dim) cells was diminished. In a control group, the proportion of CD56(Bright) NK-cells was significantly higher in secondary lymphoid tissues compared to the peripheral blood of the same individual. Our findings confirm that CD56(Bright) NK-cells preferably locate within the secondary lymphoid tissues, where they may interact with T cells and thereby contribute to the control of the disease activity in MS.

Granzyme B and natural killer (NK) cell death

Granzyme B is a unique serine protease, which plays a crucial role for target cell death. Several mechanisms of delivery of granzyme B to target cells have been recently identified. Granzyme B directly activates Bid, a specific substrate for granzyme B, resulting in caspase activation. Granzyme B efficiently cleaves many prominent autoantigens, and the hypothesis that autoantibodies arise when cryptic determinants are revealed to the immune system has been proposed. Some autoantibodies directed against granzyme B-specific neoepitopes are present in serum from patients with autoimmune diseases. In the tissues from autoimmune diseases, granzyme B might play an important role for disease progression (i.e., rheumatoid arthritis synovium) or inhibition (i.e., regulatory T cells). We have identified a novel type of activation-induced cell death (granzyme B leakage-induced cell death). Activation-induced natural killer (NK) cell death is accompanied by the leakage of granzyme B from intracellular granules into the cytoplasm, and it triggers apoptosis by directing Bid to mitochondrial membranes. An excess of "leaked" granzyme B over its inhibitor, serpin proteinase inhibitor 9, is a major determinant of cell death. The role of granzyme B in autoimmunity and its influence on NK cell death are discussed.

Deficiency of invariant natural killer T cells in coeliac disease

BACKGROUND

Immunoregulatory invariant natural killer (iNK) T cells rapidly produce interleukin (IL)-4 and other cytokines that suppress a Th1 response and are deficient in some autoimmune diseases.

AIM

The aim of this study was to investigate any deficiency of iNK T cells in coeliac disease.

METHODS

Blood was collected from 86 subjects with coeliac disease and from 152 healthy control subjects for investigation of Valpha24+ T cells by flow cytometry. iNK T cells were assessed by Valpha24 and alpha-galactosylceramide/CD1d tetramer markers in 23 normal controls and 13 subjects with coeliac disease. Intracellular IL-4 was measured after anti-CD3 antibody stimulation. Duodenal biopsies were obtained in a subgroup of subjects with coeliac disease and control subjects for Valpha24 mRNA expression using relative PCR and for Valpha24+ T cells by immunofluorescence.

RESULTS

The mean numbers of circulating Valpha24+ T cells and iNK T cells in coeliac disease were 27% (p<0.001) and 16% (p<0.001), respectively, of levels in control subjects. After in vitro anti-CD3 stimulation, numbers of IL-4+ producing iNK T cells from subjects with coeliac disease were unchanged but increased by 21% in control subjects. In subjects with coeliac disease, Valpha24 mRNA intestinal expression was reduced to 17% (p<0.001) by relative PCR and numbers of intestinal Valpha24+ T cells were 16% (p<0.01) of levels in control subjects.

CONCLUSIONS

We conclude that Valpha24+ T cells and iNK T cells are deficient in coeliac disease. We speculate that this deficiency could contribute to the failure of immunological oral tolerance that seems to underlie this disease.

Deficiency of invariant NK T cells in Crohn's disease and ulcerative colitis

The aim of this study was to investigate whether immunoregulatory invariant NK T cells are deficient in Crohn's disease or ulcerative colitis. Blood was collected for flow cytometry from 106 Crohn's disease, 91 ulcerative colitis, and 155 control subjects. Invariant NK T cells were assessed by Valpha24 and (alpha-galactosylceramide/CD1d tetramer markers. Intracellular cytokine was measured after in vitro anti-CD3 antibody stimulation. Valpha24+ T cells were quantified in ileocolonic biopsies as mRNA by real-time PCR and by immunofluorescence. Circulating invariant NK T cells were 5.3% of the control levels in Crohn's (P < 0.001) and 7.9% of the control levels in ulcerative colitis (P < 0.001). Interleukin-4 production was impaired in Crohn's disease and ulcerative colitis. Intestinal Valpha24 mRNA expression was 7% in Crohn's disease (P < 0.05) and 9% in ulcerative colitis (P < 0.05). Intestinal Valpha24+ T cells were 23% in Crohn's disease but not reduced in ulcerative colitis. We conclude that invariant NK T cells are deficient in Crohn's disease and in ulcerative colitis.

Paralysis of CD4(+)CD25(+) regulatory T cell response in chronic autoimmune encephalomyelitis

Increasing evidence strongly suggest that CD4(+)CD25(+) regulatory T (Treg) cells play a pivotal role in suppressing the development of autoimmune diseases. However, it remains poorly understood how these cells are involved in the persistence of, or recovery from, the diseases. In the present study, we examined the role of CD4(+)CD25(+) Treg cells in chronic EAE and compared the results with those obtained in acute EAE. In EAE lesions, CD25(+) cells decreased rapidly at the beginning of chronic EAE, whereas these cells were maintained at high levels during the recovery from acute EAE. The number of Foxp3(+)CD4(+)CD25(+) Treg and levels of Foxp3 mRNA in the lymphoid organ were significantly lower in chronic EAE. Importantly, the regulatory function of individual CD4(+)CD25(+) Treg cells was maintained in animals with chronic EAE. Furthermore, adoptive transfer of activated CD4(+)CD25(+) Treg cells suppressed the development of chronic EAE. These findings suggest that impairment of the CD4(+)CD25(+) Treg response is critical for development of chronic autoimmune diseases, and can be adjustable by autologous Treg transplantation.

Beta-interferon unbalances the peripheral T cell proinflammatory response in experimental autoimmune encephalomyelitis

Interferon beta (IFNbeta) is a widespread therapy for multiple sclerosis (MS). We have analyzed some critical features of the T cell activation process in lymph nodes after IFNbeta treatment of experimental autoimmune encephalomyelitis (EAE) in SJL mice. Prevention of clinical signs and drastic reduction of perivascular infiltrates in the central nervous system (CNS) were accompanied by alterations in nuclear DNA binding activity levels of NFkappaB and Stat6 transcription factors in lymph node cells (LNC). A decrease of active NFkappaB subunits in treated animals correlated with lower levels of the cytoplasmic phosphorylated form of IkappaBalpha. Results also showed that nuclear DNA binding activity of Stat6 was increased by IFNbeta treatment, as were the cytoplasmic levels of phosphorilated Stat6 (P-Stat6). These high levels of P-Stat6 in IFNbeta-treated animals were accompanied by an increase of IL-4 expression levels measured by real time PCR. In vitro experiments with the IL-4 producing clone D10.G4.1 indicates that the IFNbeta-mediated IL-4 induction is not an effect exclusive to MBP-reactive cells, and suggest that it could be mediated by mRNA stability enlargement. On the other hand, IFNbeta treatment of EAE produced no significant changes in peripheral IFNgamma expression and a striking decrease of IL-17. These findings suggest that the inhibition of NFkappaB activity, the increase of IL-4 expression and its signaling transduction, and the decrease of IL-17 may cooperate to some of the antiinflammatory effects of IFNbeta on EAE.

Antigen-activated human T lymphocytes express cell-surface NKG2D ligands via an ATM/ATR-dependent mechanism and become susceptible to autologous NK- cell lysis

Recent evidence indicates that natural killer (NK) cells can negatively regulate T-cell responses, but the mechanisms behind this phenomenon as a consequence of NK-T-cell interactions are poorly understood. We studied the interaction between the NKG2D receptor and its ligands (NKG2DLs), and asked whether T cells expressed NKG2DLs in response to superantigen, alloantigen, or a specific antigenic peptide, and if this rendered them susceptible to NK lysis. As evaluated by FACS, the major histocompatibility complex (MHC) class I chain-related protein A (MICA) was the ligand expressed earlier on both CD4(+) and CD8(+) T cells in 90% of the donors tested, while UL16-binding protein-1 (ULBP)1, ULBP2, and ULBP3 were induced at later times in 55%-75% of the donors. By carboxyfluorescein diacetate succinimidyl ester (CFSE) labeling, we observed that NKG2DLs were expressed mainly on T cells that had gone through at least one division. Real-time reverse-transcription polymerase chain reaction confirmed the expression of all NKG2DLs, except ULBP4. In addition, T-cell activation stimulated phosphorylation of ataxia-telangiectasia mutated (ATM), a kinase required for NKG2DLs expression after DNA damage, and ATM/Rad3-related kinase (ATR) inhibitors blocked MICA induction on T cells with a mechanism involving NF-kappaB. Finally, we demonstrated that activated T cells became susceptible to autologous NK lysis via NKG2D/NKG2DLs interaction and granule exocytosis, suggesting that NK lysis of T lymphocytes via NKG2D may be an additional mechanism to limit T-cell responses.

NK3-like NK cells are involved in protective effect of polyinosinic-polycytidylic acid on type 1 diabetes in nonobese diabetic mice

Type 1 diabetes in NOD mice is characterized by the uncontrolled Th1 immune responses and deficiency of regulatory or suppressor cells. Previous study has shown that NOD mice treated with polyinosinic-polycytidylic acid (poly(I:C)) have a markedly reduced incidence of diabetes, but the underlying mechanisms remain unclear. In this study, we report that the prevention of diabetes by poly(I:C) is associated with the formation of Th2-enriched environment in spleen and pancreas. We further show that the prevention of diabetes and the formation of Th2-enriched environment depend on the presence of NK cells. Long-term poly(I:C)-treated NK cells exhibit a NK3-like phenotype, and are involved in the induction of Th2 bias of spleen cells in response to islet autoantigens via TGF-beta-dependent manner. Therefore, NK cells mediate the protective effect of poly(I:C) possibly through the promotion of Th2 bias of immune responses. These findings suggest that NK cells can participate in the regulation of autoimmune diabetes.

T Helper Type 2-Biased Natural Killer Cell Phenotype in Patients with Pemphigus Vulgaris

Pemphigus vulgaris (PV) is an autoantibody-mediated bullous disease, but the role of natural killer (NK) cells in its pathogenic process has never been examined in detail. Circulating CD56+ CD3- NK cells as well as CD69+-activated NK cells were increased in PV patients compared with healthy controls and patients with other autoantibody-mediated autoimmune diseases, including immune thrombocytopenic purpura and myasthenia gravis. Gene expression analysis of highly purified NK cells demonstrated an increased expression of IL-10 and decreased expression of IL-12Rbeta2, perforin, and granzyme B ex vivo in PV patients versus healthy controls. The NK cells from PV patients also showed impaired signal transducer and activator of transduction4 phosphorylation upon in vitro IL-12 stimulation. Moreover, NK cells from PV patients exhibited reduced IL-10 production in response to in vitro stimulation with IL-2/IL-12. Finally, IL-5 expression in NK cells was exclusively detected ex vivo in PV patients with active disease, and was lost in subsequent analyses performed during disease remission. Together these findings suggest that NK cells contribute to a T helper type 2-biased immune response in PV patients through impaired IL-12 signaling and an upregulation of IL-10 and IL-5.

The role of the ICOS/B7RP-1 T cell costimulatory pathway in murine experimental autoimmune uveoretinitis

ICOS/B7RP-1 is a new member of the CD28/B7 family of costimulatory molecules and plays differential roles in autoimmune diseases. In this study, we examined the role of ICOS/B7RP-1 pathway in the pathogenesis of mouse experimental autoimmune uveoretinitis (EAU), an animal model of human autoimmune uveitis. ICOS expression was found on infiltrating CD4+ T cells in the region of the retina in EAU-induced mice. The anti-B7RP-1 monoclonal antibody (mAb)-treated or ICOS-deficient mice showed a substantial reduction of disease scores. Blockade of ICOS/B7RP-1 interaction during the effector phase ameliorated the disease, whereas its blockade during the induction phase exhibited no significant effect. Moreover, administration of anti-B7RP-1 mAb effectively ameliorated the disease induced by adoptive transfer of pathogenic T cells. The anti-B7RP-1 mAb treatment inhibited the expansion and/or effector function of pathogenic T cells, given that proliferative response and IFN-gamma production by lymph node cells were reduced upon restimulation with the antigen peptide in vitro. These results suggest that the ICOS/B7RP-1 interaction plays a critical role in the pathogenesis of uveitis. We also indicated that ICOS-mediated costimulation plays differential roles in EAU and experimental autoimmune encephalomyelitis, which is also a Th1 disease induced in the same manner as EAU.

Anti-Tac (daclizumab, Zenapax) in the treatment of leukemia, autoimmune diseases, and in the prevention of allograft rejection: a 25-year personal odyssey

Twenty-five years ago, we reported the production of the monoclonal antibody, anti-Tac that identifies the IL-2 receptor alpha subunit and blocks the interaction of IL-2 with this growth factor receptor. In 1997, daclizumab (Zenapax), the humanized form of this antibody, was approved by the FDA for use in the prevention of renal allograft rejection. In addition, we demonstrated that daclizumab is of value in the treatment of patients with noninfectious uveitis, multiple sclerosis, and the neurological disease human T-cell lymphotropic virus I associated myelopathy/tropical spastic paraparesis (HAM/TSP). Others demonstrated therapeutic efficacy with daclizumab in patients with pure red cell aplasia, aplastic anemia, and psoriasis. Thus, translation of basic insights concerning the IL-2/IL-2 receptor system obtained using the monoclonal antibody daclizumab provided a useful strategy for the prevention of organ allograft rejection and the treatment of patients with select autoimmune diseases or T-cell leukemia/lymphoma.

Chemokines and chemokine receptors: multipurpose players in neuroinflammation

Chemokines were detected by virtue of chemotactic effects toward neutrophils in the late 1970s. During subsequent decades, it has become clear that their primordial role in vertebrate biology was to facilitate organogenesis, with particularly important functions in the central nervous system (CNS). In common with other developmentally relevant factors, chemokines and their G-protein-coupled receptors continue to be expressed in the adult CNS as neuromodulators. In our progress toward chemokine receptor blockade for treatment of inflammatory and infectious diseases, the CNS physiology of the chemokine system will need to be a material consideration. In some cases, the dual functions of the chemokine system in the periphery and in the CNS offer unique possibilities for disease treatment.

Reciprocal regulation between natural killer cells and autoreactive T cells

The initiation and the progression of autoimmune diseases stem from complex interactions that involve cells of both the innate and the adaptive immune system. As we discuss here, natural killer (NK) cells, which are components of the innate immune system, can inhibit or promote the activation of autoreactive T cells during the initiation of autoimmunity. After they have been activated, autoreactive T cells contribute to the homeostatic contraction of NK-cell populations. The dynamic interaction between NK cells and autoreactive T cells might indicate the transition from the innate immune triggering of autoimmunity to the progressive phase of the disease. Understanding the mechanisms and signals that control the reciprocal regulation of NK cells and autoreactive T cells could have important implications for treatment in the clinic.

[Leptin: a link between obesity and osteoarthritis?]

In addition to aging, obesity is one of the most common underlying causes of osteoarthritis (OA). Mechanical loading, together with biochemical and systemic factors linked to altered lipid metabolism, are thought to contribute to the onset of OA. It has been suggested that OA is a systemic metabolic disease associated with lipid disorders affecting joint homeostasis. These gradual changes may be due to the local effect of adipokines, and especially leptin. Indeed, their relative levels in joints differ from that found in plasma. In particular, leptin levels are increased and adiponectin and resistin levels are reduced This hypothesis is supported by--leptin overexpression in OA cartilage and its correlation with the degree of cartilage destruction,--abundant leptin synthesis by osteophytes, and--the high leptin levels found in OA joints from female patients. This link between OA and adipokines provides new leads regarding the prevention of OA and the identification of new drug targets.

Persistence of CD16+/CD56-/2B4+ natural killer cells: a highly dysfunctional NK subset expanded in ocular myasthenia gravis

We report a case of myasthenia gravis associated with marked expansion of an unusual CD16(+)CD56(-)2B4(+) NK subset. These atypical cells were characterized by poor cytotoxicity against CD48(+) target cells and high proliferation due to 2B4/CD48 interaction. IL18, IFN-gamma and TGF-beta levels were profoundly different in this patient than in healthy donors. Immunosuppressive treatment induced disease remission and decreased the CD16(+)CD56(-)2B4(+)NK cells count. Our data suggest that expansion of this NK subset in myasthenia gravis patients may account for the deleterious NK cell functioning that occurs in this autoimmune disease.

Characterization of peripheral natural killer cells in primary Sjögren's syndrome: impaired NK cell activity and low NK cell number

The aim of this study was to compare the number of peripheral blood natural killer (NK) cells, NK cell activity, expression of NK cell activating receptors, and serum cytokine levels in patients with primary Sjögren's syndrome (SS) vs normal controls. The authors found that NK cell number, NK cell killing activity, and the expression of activating receptors CD2 and NKG2D were significantly decreased, and the expression of NKp46, as well as the percentage of apoptotic NK cells, were significantly increased in primary SS patients compared with healthy controls. NK cell killing activity on a per-cell basis was similar in primary SS patients and healthy controls. Moreover, the levels of IL-18 and TNF-alpha, cytokines that have been shown to promote NK cell death, were significantly increased in sera from patients with primary SS compared with controls. These data suggest that reduced NK cell numbers, probably a result of apoptotic death, may contribute to impaired NK cell activity in patients with primary SS.

The neuronal chemokine CX3CL1/fractalkine selectively recruits NK cells that modify experimental autoimmune encephalomyelitis within the central nervous system

Leukocyte trafficking to the central nervous system (CNS), regulated in part by chemokines, determines severity of the demyelinating diseases multiple sclerosis (MS) and experimental autoimmune encephalomyelitis (EAE). To examine chemokine receptor CX3CR1 in EAE, we studied CX3CR1(GFP/GFP) mice, in which CX3CR1 targeting by insertion of Green Fluorescent Protein (GFP) allowed tracking of CX3CR1+ cells in CX3CR1(+/GFP) animals and cells destined to express CX3CR1 in CX3CR1(GFP/GFP) knockouts. NK cells were markedly reduced in the inflamed CNS of CX3CR1-deficient mice with EAE, whereas recruitment of T cells, NKT cells and monocyte/macrophages to the CNS during EAE did not require CX3CR1. Impaired recruitment of NK cells in CX3CR1(GFP/GFP) mice was associated with increased EAE-related mortality, nonremitting spastic paraplegia and hemorrhagic inflammatory lesions. The absence of CD1d did not affect the severity of EAE in CX3CR1(GFP/GFP) mice, arguing against a role for NKT cells. Accumulation of NK cells in livers of wild-type (WT) and CX3CR1(GFP/GFP) mice with cytomegalovirus hepatitis was equivalent, indicating that CX3CL1 mediated chemoattraction of NK cells was relatively specific for the CNS. These results are the first to define a chemokine that governs NK cell migration to the CNS, and the findings suggest novel therapeutic manipulation of CX3CR1+ NK cells.

Increased killing activity and decreased cytokine production in NK cells in patients with primary biliary cirrhosis

Although the pathogenesis of primary biliary cirrhosis (PBC) remains enigmatic, the immune system plays a key role in the initiation and subsequent development of pathology. Previous studies have indicated a critical role of the innate immune system. Importantly, natural killer (NK) cells are abundant in liver where they serve as sentinels of the immune system. In addition, NK cells have significant biologic activity based on their production of immunoregulatory cytokines. To address this issue, we have investigated several qualitative and quantitative activities of NK cells in patients with PBC as well as normal and liver diseased controls. We report herein a marked increase in the frequency and absolute number of blood and liver NK cells in PBC patients. Moreover, the cytotoxic activity and perforin expression by isolated NK cells were significantly increased in PBC patients associated with increased levels of plasma IL-8 and the expression of CD128a (IL-8 receptor) on NK cells. In contrast, the levels of IFN-gamma, IL-6 and IL-8 synthesized by NK cells were significantly decreased in PBC patients as compared to controls. In conclusion, data from this study provide compelling evidence supporting a biologic role of NK cells in the immunopathogenesis of PBC.

Autoreactive T Cells Mediate NK Cell Degeneration in Autoimmune Disease

Emerging evidence indicates that NK cells play an important and complex role in autoimmune disease. Humans with autoimmune diseases often have reduced NK cell numbers and compromised NK cell functions. Mechanisms underlying this NK cell degeneration and its biological significance are not known. In this study we show that, in an experimental model of human autoimmune myasthenia gravis induced by a self-Ag, the acetylcholine receptor, NK cells undergo proliferation during the initiation of autoimmunity, followed by significant degeneration associated with the establishment of the autoreactive T cell response. We show that NK cell degeneration was mediated by IL-21 derived from autoreactive CD4(+) T cells, and that acetylcholine receptor-immunized IL-21R-deficient mice, with competent NK cells, developed exacerbated autoimmunity. Thus, NK cell degeneration may serve as a means evolved by the immune system to control excessive autoimmunity.