Diagnostic performance of sacroiliac joint MRI and added value of spine MRI to detect active spondyloarthritis.

PURPOSE: To investigate the diagnostic performance of sacroiliac joint (SIJ) magnetic resonance imaging (MRI) and the incremental value of spine MRI to "predict" clinical disease activity in patients with axial spondyloarthritis (axSpA). MATERIALS AND METHODS: This cross-sectional study included adult patients with known axSpA according to the SpondyloArthritis International Society (ASAS) classification criteria, radiological arm. MRI disease activity was scored semi-quantitatively for SIJ and total spine MRI in each patient. Two cut-off levels (≥ 1.3 and ≥ 2.1) for ankylosing spondylitis disease activity score with C-reactive protein (ASDAS-CRP) were considered for clinical disease activity categorization. MRI scores were first evaluated individually. Then, SIJ score was combined with the score from a spine segment (lumbar, cervical, thoracic or total spine) to build a bi-parametric model using a classification tree. Receiver operating characteristic (ROC) curves were constructed to evaluate the classification performance according to disease activity category of these models. RESULTS: Forty-four patients (30 men, 14 women; mean age, 37 years±10 [SD] [range: 17-64 years]) with a mean disease duration of 5 years±8 (SD) (range: 0-35 years) were included. Thirty-six patients (36/44; 82%) had ASDAS-CRP≥1.3 and 27 patients (27/44; 61%) had ASDAS-CRP≥2.1. The most frequently involved spinal segment was mid-thoracic (T7-T8). The SIJ MRI score was an informative model to identify active axSpA (AUC≥0.7, regardless of the cut-off level on ASDAS-CRP). Performance of bi-parametric models based on "SIJ+thoracic spine" (for detecting patients with ASDAS-CRP≥1.3) or "SIJ+total spine" (for detecting patients with ASDAS-CRP≥2.1) outperformed that of the individual SIJ score (P<0.05). CONCLUSION: The combination of MRI of the SIJ and spine allows to accurately discriminate between active and inactive axSpA, outperforming SIJ MRI alone.

Drug repositioning in SLE: crowd-sourcing, literature-mining and Big Data analysis.

Lupus patients are in need of modern drugs to treat specific manifestations of their disease effectively and safely. In the past half century, only one new treatment has been approved by the US Food and Drug Administration (FDA) for systemic lupus erythematosus (SLE). In 2014-2015, the FDA approved 71 new drugs, only one of which targeted a rheumatic disease and none of which was approved for use in SLE. Repositioning/repurposing drugs approved for other diseases using multiple approaches is one possible means to find new treatment options for lupus patients. "Big Data" analysis approaches this challenge from an unbiased standpoint whereas literature mining and crowd sourcing for candidates assessed by the CoLTs (Combined Lupus Treatment Scoring) system provide a hypothesis-based approach to rank potential therapeutic candidates for possible clinical application. Both approaches mitigate risk since the candidates assessed have largely been extensively tested in clinical trials for other indications. The usefulness of a multi-pronged approach to drug repositioning in lupus is highlighted by orthogonal confirmation of hypothesis-based drug repositioning predictions by "Big Data" analysis of differentially expressed genes from lupus patient samples. The goal is to identify novel therapies that have the potential to affect disease processes specifically. Involvement of SLE patients and the scientists that study this disease in thinking about new drugs that may be effective in lupus though crowd-sourcing sites such as LRxL-STAT (www.linkedin.com/in/lrxlstat) is important in stimulating the momentum needed to test these novel drug targets for efficacy in lupus rapidly in small, proof-of-concept trials conducted by LuCIN, the Lupus Clinical Investigators Network (www.linkedin.com/in/lucinstat).

sIL7R concentrations in the serum reflect disease activity in the lupus kidney.

OBJECTIVES: Evaluation of disease activity in systemic lupus erythematosus (SLE) nephritis is a challenge, and repeated renal biopsies are usually needed in order to confirm a suspicion of flare. In a previous cross-sectional study, we reported that serum soluble form of the interleukin-7 receptor (sIL7R) levels is strongly associated with nephritis in SLE patients. In the present study, we wanted to confirm the association between changes in serum sIL7R concentrations and renal disease activity in a large longitudinal cohort of SLE nephritis patients. METHODS: Sera were harvested longitudinally in 105 SLE nephritis patients. Serum sIL7R cut-off value for the detection of SLE nephritis activity was determined as the mean sIL7R concentration in non-nephritis SLE patients + 2 SDs using data collected in our previous study. Patients with glomerular filtration rate (GFR) <60 mL/min/1.73 m(2) (n=17) were excluded from the study due to persistently elevated serum sIL7R values. RESULTS: Serum sIL7R concentrations above the renal cut-off value were observed in 25 (out of 88) patients with a normal GFR. These patients had significantly higher serum double-stranded DNA (dsDNA) Ab and urinary protein to creatinine (UPC) ratio. Strikingly, 12 of them developed a renal British Isles Lupus Assessment Group index (BILAG) A within the next 3 months, while this was only the case in four out of the 63 other patients (p<0.0001). The test had 75.0% sensitivity and 81.9% specificity for the detection of a renal BILAG A. Combination of serum sIL7R with any of the classical tests (anti-dsDNA Ab titres, UPC ratio, serum C3) resulted in an increased specificity for the detection of a renal flare. Administration of immunosuppressive therapy resulted in a significant decrease in serum sIL7R concentrations. CONCLUSIONS: Serum sIL7R is a sensitive and specific marker of renal disease activity in SLE. Elevated serum sIL7R values in SLE patients are associated with or predict the occurrence of an SLE nephritis flare.

Genetic association of miRNA-146a with systemic lupus erythematosus in Europeans through decreased expression of the gene.

A recent genome-wide association study revealed a variant (rs2431697) in an intergenic region, between the pituitary tumor-transforming 1 (PTTG1) and microRNA (miR-146a) genes, associated with systemic lupus erythematosus (SLE) susceptibility. Here, we analyzed with a case-control design this variant and other candidate polymorphisms in this region together with expression analysis in order to clarify to which gene this association is related. The single-nucleotide polymorphisms (SNPs) rs2431697, rs2910164 and rs2277920 were genotyped by TaqMan assays in 1324 SLE patients and 1453 healthy controls of European ancestry. Genetic association was statistically analyzed using Unphased. Gene expression of PTTG1, the miRNAs miR-3142 and primary and mature forms of miR-146a in peripheral blood mononuclear cells (PBMCs) were assessed by quantitative real-time PCR. Of the three variants analyzed, only rs2431697 was genetically associated with SLE in Europeans. Gene expression analysis revealed that this SNP was not associated with PTTG1 expression levels, but with the microRNA-146a, where the risk allele correlates with lower expression of the miRNA. We replicated the genetic association of rs2341697 with SLE in a case-control study in Europeans and demonstrated that the risk allele of this SNP correlates with a downregulation of the miRNA 146a, potentially important in SLE etiology.

Rituximab treatment induces the expression of genes involved in healing processes in the rheumatoid arthritis synovium.

OBJECTIVE: Rituximab displays therapeutic benefits in the treatment of patients with rheumatoid arthritis (RA) resistant to tumor necrosis factor (TNF) blockade. However, the precise role of B cells in the pathogenesis of RA is still unknown. We undertook this study to investigate the global molecular effects of rituximab in synovial biopsy samples obtained from anti-TNF-resistant RA patients before and after administration of the drug. METHODS: Paired synovial biopsy samples were obtained from the affected knee of anti-TNF-resistant RA patients before (time 0) and 12 weeks after (time 12) initiation of rituximab therapy. Total RNA was extracted, labeled according to standard Affymetrix procedures, and hybridized on GeneChip HGU133 Plus 2.0 slides. Immunohistochemistry and quantitative real-time reverse transcriptase-polymerase chain reaction experiments were performed to confirm the differential expression of selected transcripts. RESULTS: According to Student's paired t-tests, 549 of 54,675 investigated probe sets were differentially expressed between time 0 and time 12. Pathway analysis revealed that genes down-regulated between time 0 and time 12 were significantly enriched in immunoglobulin genes and genes involved in chemotaxis, leukocyte activation, and immune responses (Gene Ontology annotations). In contrast, genes up-regulated between time 0 and time 12 were significantly enriched in transcripts involved in cell development (Gene Ontology annotation) and wound healing (Gene Set Enrichment Analysis). At baseline, higher synovial expression of immunoglobulin genes was associated with response to therapy. CONCLUSION: Rituximab displays unique effects on global gene expression profiles in the synovial tissue of RA patients. These observations open new perspectives in the understanding of the biologic effects of the drug and in the selection of patients likely to benefit from this therapy.

[Identification of new diagnostic and therapeutic markers in rheumatoid arthritis]. / Identification de nouveaux marqueurs diagnostiques et thérapeutiques dans la polyarthrite rhumatoïde.

Our work aims at the identification of new diagnostic and prognostic markers in rheumatoid arthritis (RA), using synovial biopsies in patients. We first demonstrated that the molecular signatures identified in these biopsies enable us to differentiate patients with early RA from patients suffering from other inflammatory conditions. Next, we performed transcriptomic studies in synovial biopsies harvested from patients with severe RA before and twelve weeks after initiation of TNF blocking or rituximab (depleting anti-CD20 antibody) therapy. These studies enabled us to identify specific molecular signatures targeted by these therapies in the synovium, and novel markers of response to therapy. Our results open interesting perspectives in terms of potential biomarkers, which could be used in order to improve diagnostic performances and therapeutic decisions based on individual molecular characteristics of the patients.

Rheumatoid arthritis synovial fibroblasts produce a soluble form of the interleukin-7 receptor in response to pro-inflammatory cytokines.

We previously demonstrated that baseline synovial overexpression of the interleukin-7 receptor α-chain (IL-7R) is associated with poor response to tumour necrosis factor (TNF) blockade in rheumatoid arthritis (RA). We found that IL-7R gene expression is induced in fibroblast-like synovial cells (FLS) by the addition of TNF-α, IL-1ß and combinations of TNF-α+ IL-1ß or TNF-α+ IL-17, thereby suggesting that these cytokines play a role in the resistance to TNF blockade in RA. Because FLS and CD4 T cells also produce a soluble form of IL-7R (sIL-7R), resulting from an alternative splicing of the full-length transcript, we wondered whether expression of sIL-7R is similarly regulated by pro-inflammatory cytokines. We also investigated whether sIL-7R is detectable in the serum of RA patients and associated with response to TNF blockade. RA FLS were cultured in the presence of pro-inflammatory cytokines and sIL-7R concentrations were measured in culture supernatants. Similarly, sIL-7R titres were measured in sera obtained from healthy individuals, early untreated RA patients with active disease and disease-modifying anti-rheumatic drug (DMARD)-resistant RA patients prior to initiation of TNF-blockade. Baseline serum sIL-7R titres were correlated with validated clinical measurements of disease activity. We found that exposure of RA FLS to pro-inflammatory cytokines (TNF-α, IL-1ß and combinations of TNF-α and IL-1ß or TNF-α and IL-17) induces sIL-7R secretion. Activated CD4 T cells also produce sIL-7R. sIL-7R serum levels are higher in RA patients as compared to controls. In DMARD-resistant patients, high sIL-7R serum concentrations are strongly associated with poor response to TNF-blockade. In conclusion, sIL-7R is induced by pro-inflammatory cytokines in RA FLS. sIL-7R could qualify as a new biomarker of response to therapy in RA.

Juvenile-onset systemic lupus erythematosus: different clinical and serological pattern than adult-onset systemic lupus erythematosus.

OBJECTIVE: To investigate differences in clinical signs and symptoms, and in antinuclear antibodies (ANA), between patients with juvenile-onset and adult-onset systemic lupus erythematosus (SLE). METHODS: Clinical and serological data of 56 patients with juvenile-onset SLE were compared with data of 194 patients with adult-onset SLE. ANA were determined by line immunoassay and by indirect immunofluorescence on Crithidia luciliae. RESULTS: Renal involvement, encephalopathy and haemolytic anaemia were seen, and anti-dsDNA, anti-ribosomal P and antihistone antibodies found, significantly more often in juvenile-onset SLE. Anti-dsDNA antibodies were directly associated, and anti-ribosomal P antibodies inversely associated, with renal involvement in juvenile-onset SLE. In juvenile patients with SLE and anti-dsDNA and without anti-ribosomal P antibodies the odds ratio for glomerulonephritis was 9.00; no patients with anti-ribosomal P but without anti-dsDNA had renal involvement. CONCLUSION: Patients with juvenile-onset SLE more often have renal involvement and encephalopathy than patients with adult-onset SLE. Anti-ribosomal P, anti-dsDNA and antihistone antibodies are more often found in patients with juvenile-onset SLE.

Identification of distinct gene expression profiles in the synovium of patients with systemic lupus erythematosus.

OBJECTIVE: Synovitis is a common feature of rheumatoid arthritis (RA) and systemic lupus erythematosus (SLE), but the pattern of joint involvement differs in each disease. This study was undertaken to investigate the global gene expression profiles in synovial biopsy tissue from the swollen knees of untreated SLE patients (n = 6), RA patients (n = 7), and osteoarthritis (OA) patients (n = 6). METHODS: Synovial biopsy samples were obtained from the affected knees of patients in the 3 groups by needle arthroscopy. Half of the material was used for extraction of total RNA, amplification of complementary RNA, and high-density oligonucleotide spotted hybridization arrays. On the remaining tissue samples, real-time reverse transcription-polymerase chain reaction (RT-PCR) and immunohistochemical experiments were performed to confirm the microarray data. RESULTS: SLE synovial biopsy tissue displayed a significant down-regulation of genes involved in extracellular matrix (ECM) homeostasis and a significant up-regulation of interferon-inducible (IFI) genes. Real-time RT-PCR experiments confirmed the up-regulation of selected IFI genes (IFI27, IFI44, and IFI44L) in the SLE synovial tissue. Immunohistochemical analyses showed that 3 molecules involved in ECM regulation, chondroitin sulfate proteoglycan 2, latent transforming growth factor beta binding protein 2, and fibroblast activation protein alpha, were significantly down-regulated in SLE synovium. In contrast, immunostaining for IFI27, Toll-like receptor 4, and STAT-1 resulted in higher quantitative scores in SLE synovial tissue, which could be attributed to the fact that the RA samples had a large population of inflammatory cell infiltrates that were negative for these markers. CONCLUSION: Arthritis in SLE has a very distinct molecular signature as compared with that in OA and RA, characterized by up-regulation of IFI genes and down-regulation of genes involved in ECM homeostasis.

Genetics of lupus nephritis.

Susceptibility to lupus nephritis is the end-result of complex interactions between polymorphic genetic factors involved in the regulation of immune responses. In humans, genome-wide screens and candidate-gene analyses led to the identification of several loci containing potential targets (FcgammaRIIa, PTPN22, PD-1, IL-10) for physiopathological research and therapeutic interventions. In mice, the generation of congenic mice, bearing in a normal genetic background one single disease-associated locus, greatly improved our understanding of the mechanisms mediating the genetic contribution to the disease. In the future, the identification of disease-associated genes will open new perspectives for the development of more targeted therapies of lupus nephritis.

A randomised comparative study of the short term clinical and biological effects of intravenous pulse methylprednisolone and infliximab in patients with active rheumatoid arthritis despite methotrexate treatment.

OBJECTIVES: To compare the short term clinical and biological effects of intravenous (i.v.) pulse methylprednisolone (MP) and infliximab (IFX) in patients with severe active rheumatoid arthritis (RA) despite methotrexate (MTX) treatment. METHODS: Patients with active RA despite MTX treatment were randomly allocated to receive a single i.v. infusion of MP (1 g) or three i.v. infusions of IFX (3 mg/kg) on weeks 0, 2, and 6. Patients were "blindly" evaluated for disease activity measures. Quality of life (QoL) was evaluated through the SF-36 health survey. Serum matrix metalloproteinase-3 (MMP-3) titres were measured at baseline, weeks 2 and 6. RESULTS: Compared with baseline, significant improvement was noted in all activity measures, including serum C reactive protein (CRP) titres, in the IFX group only. At week 14, 6/9 (67%) and 4/9 (44%) IFX patients met the ACR20 and 50 response criteria, while this was the case in only 1/12 (8%) and 0/12 (0%) MP patients, respectively (p<0.05). None of the QoL scales improved with MP treatment, whereas some did so in the IFX group. Serum MMP-3 titres significantly decreased (41% drop) at week 6 in the IFX group, while no changes were seen in patients given MP. CONCLUSION: This short term randomised comparative study demonstrates that TNF blockade is better than MP pulse therapy in a subset of patients with severe refractory RA, with improvement in not only clinical parameters of disease activity but also biological inflammatory indices, such as serum CRP and MMP-3 titres.

[New studies of the physiopathologic mechanisms of disseminated lupus erythematosus]. / Nouvelles recherches sur le mécanisme physiopathologique du lupus erythémateux disséminé.

Recent work about the role of cytokines in the pathogenesis of systemic lupus has shed new light on the important contribution of IL-10 and BAFF, to the production of pathogenic autoantibodies and the development of disease. Together with the advances in the biotechnologies, these contributions will allow to develop novel therapeutic approaches targeting the immune system of lupus patients.

Serum IL-12 in systemic lupus erythematosus: absence of p70 heterodimers but presence of p40 monomers correlating with disease activity.

Biologically active IL-12 is a 70 kDa heterodimeric cytokine (IL-12 p70) mainly produced by antigen-presenting cells (APC) and made of disulfide-linked alpha (p35) and beta (p40) chains. Since the production of the p40 subunit is independently regulated from that of IL-12 p70, we compared levels of p40 and IL-12 p70 in the sera of patients with systemic lupus erythematosus (SLE). Sera obtained from rheumatoid arthritis (RA) patients and healthy subjects were used as controls. Serum p40 titers were significantly higher in SLE patients (mean +/- s.e.m.: 348 +/- 40 pg/ml) compared with patients with rheumatoid arthiritis (mean +/- s.e.m.: 116 +/- 18 pg/ml, P < 0.0001) or controls (mean +/- s.e.m.: 0 +/- pg/ml, P < 0.0001). By contrast, IL-12 p70 was not detected in any serum. In SLE patients, serum p40 levels were positively correlated with the SLEDAI (r = + 0.56, P = 0.02) and negatively with serum C3 levels (r = - 0.42, P = 0.03). Follow-up measurements indicated that serum p40 dropped significantly after immunosuppressive therapy. Finally, size exclusion chromatography with p40 immunoprecipitates obtained from SLE sera demonstrated that p40 was present as a monomer, and not as a homodimer, nor as a p19/p40 (IL-23) heterodimer. In conclusion, serum p40 monomers (but not IL-12 p70 titers) are elevated in the sera of SLE patients commensurate with disease activity. While the relevance of these observations needs to be further investigated, our results are consistent with the APC dysfunction described in SLE.

Myocardial microangiopathy associated with antiphospholipid antibodies.

Myocardial thrombotic microangiopathy is a well described post-mortem finding in patients with the catastrophic antiphospholipid (APL) syndrome. However, it has been only very rarely imaged in living patients. Here, we report two patients with APL antibodies presenting with scintigraphic, electrocardiographic and/or echocardiographic evidence of (sub)acute myocardial ischaemia, despite a normal coronary angiography. Formal proof of a thrombotic microangiopathy was obtained by a kidney biopsy in one patient. We emphasize the value of 99mTc-MIBI (2-methoxy isobutyl isonitrile) exercise stress myocardial scintigraphy for the detection of cardiac microangiopathy associated with the APL syndrome.

Interleukin-10 blockade corrects impaired in vitro cellular immune responses of systemic lupus erythematosus patients.

OBJECTIVE: Many systemic lupus erythematosus (SLE) patients display impaired cellular immune responses against allo- or recall antigens. Given the down-regulating properties of interleukin-10 (IL-10) on antigen-presenting cell functions, this study was undertaken to investigate whether the well-known overproduction of IL-10 by SLE peripheral blood mononuclear cells (PBMC) was involved in this process. METHODS: We measured the proliferation of SLE or control PBMC against irradiated allogeneic dendritic cells in the absence or presence of antibodies blocking IL-10 activity, or in the absence or presence of IL-12. RESULTS: As a group, SLE PBMC proliferated against allogeneic targets less than control PBMC. However, SLE patients could be categorized as good responders or poor responders according to the amplitude of their allogeneic response. Interestingly, serum IL-10 concentrations were significantly higher in the poor responders than in the good responders or in the controls, and addition of antibodies blocking IL-10 activity significantly increased the proliferative responses of the group. We confirmed the role of IL-10 in the impaired allogeneic responses displayed by SLE PBMC by demonstrating that addition of IL-10-containing SLE PBMC supernatants inhibited a normal allogeneic response between unrelated healthy controls, and by showing that this inhibitory effect was commensurate with the concentrations of IL-10 measured in the supernatants. In this experimental setting, we also demonstrated that IL-10-containing SLE PBMC supernatants inhibited IL-12 p35 and IL-12 p40 gene expression. Consistent with the last observation, we found that addition of exogenous IL-12 restored the proliferation of poor-responder SLE patients' PBMC. CONCLUSION: Taken together, these results indicate that dysregulation of the IL-10/IL-12 balance plays a critical role in the impaired cellular immune responses observed in SLE patients.

Cytokine production and killer activity of NK/T-NK cells derived with IL-2, IL-15, or the combination of IL-12 and IL-18.

NK cell populations were derived from murine splenocytes stimulated by IL-2, IL-15, or the combination of IL-12 and IL-18. Whereas NK cells derived with the latter cytokines consisted of an homogeneous population of NK cells (DX5+CD3-), those derived with IL-2 or IL-15 belonged to two different populations, namely NK cells (DX5+CD3-) and T-NK cells (DX5+CD3+). Among NK cells, only those derived with IL-12/IL-18 produced detectable levels of cytokines, namely IFN-gamma, IL-10, and IL-13 (with the exception of IL-13 production by NK cells derived with IL-2). As for T-NK cells, IL-2-stimulated cells produced a wide range of cytokines, including IL-4, IL-5, IL-9, IL-10, and IL-13, but no IFN-gamma, whereas IL-15-derived T-NK cells failed to produce any cytokine. Switch-culture experiments indicated that T-NK cells derived in IL-2 and further stimulated with IL-12/IL-18 produced IFN-gamma and higher IL-13 levels. Next, we observed that NK/T-NK cell populations exerted distinct effects on Ig production by autologous splenocytes according to the cytokines with which they were derived. Thus, addition of NK cells derived in IL-12/IL-18 inhibited Ig production and induced strong cytotoxicity against splenocytes, whereas addition of NK or T-NK cells grown in IL-2 or IL-15 did not. Experiments performed in IFN-gammaR knockout mice demonstrated that IFN-gamma was not involved in the killer activity of IL-12/IL-18-derived NK cells. The hypothesis that their cytotoxic activity was related to the induction of target apoptosis was confirmed on murine A20 lymphoma cells. Experiments performed in MRL/lpr mice indicated that IL-12/IL-18-derived NK cells displayed their distinct killer activity through a Fas-independent pathway. Finally, perforin was much more expressed in IL-12/IL-18-derived NK cells as compared with IL-2- or IL-15-derived NK cells, an observation that might explain their unique cytotoxicity.

Synergistic proliferation and activation of natural killer cells by interleukin 12 and interleukin 18.

We investigated the effects of IL-12 and IL-18 on unstimulated murine splenocytes and observed that the two cytokines strongly synergized for their proliferation, whereas IL-12 and IL-18 alone were essentially inactive in this respect. Phenotypical and functional analyses of cells proliferating in response to IL-12 and IL-18 revealed that large granular Ly-49C(+)DX5(+)CD3(-)NK blasts were expanded in these cultures and that they displayed cytotoxic activity against Yac-1 cells, a murine NK cell target. Further analyses indicated three major differences between NK cells appearing in response to IL-12 and IL-18 and those derived in the presence of other NK cell growth factors, such as IL-2 or IL-15. First, a population of T-NK cells, i.e. expressing T cell (TCRalphabeta, CD3) and NK cell (Ly-49) markers, was detected amongst cells growing in IL-2 or IL-15 but not in cultures supplemented with IL-12 and IL-18. Second, most NK cells derived with IL-2 or IL-15 expressed the NK1.1 antigen, while those derived with IL-12 and IL-18 did not. Finally, striking differences were observed regarding cytokine production. Cells stimulated with IL-12 and IL-18 in combination, but not with IL-2 or IL-15, produced IFN-gamma, IL-3, IL-6 and TNF. IFN-gamma was not involved in the response of NK cells to IL-12 and IL-18, as indicated by experiments demonstrating that the combination of the two cytokines displayed similar effects on spleen cells from IFN-gammaR-knock-out mice. Receptor (IL-12Rbeta1, IL-12Rbeta2 and IL-18R) gene expression studies did not indicate that the mechanism underlying the synergy between IL-12 and IL-18 involved reciprocal induction of their receptors. Taken together, our results demonstrate that IL-12 and IL-18 exert striking synergistic activities for NK cell proliferation and activation, distinct from those induced by IL-2 or IL-15.