An animal model of hemophagocytic lymphohistiocytosis (HLH): CD8+ T cells and interferon gamma are essential for the disorder

Familial haemophagocytic lymphohistiocytosis: advances in the genetic basis, diagnosis and management

Familial haemophagocytic lymphohistiocytosis (FHL) is a rare autosomal recessive disorder of immune dysregulation associated with uncontrolled T cell and macrophage activation and hypercytokinaemia. The incidence of FHL is 0·12/100·000 children born per year, with a male to female ratio of 1:1. The disease is classified into six different types based on genetic linkage analysis and chromosomal localization; five specific genetic defects have been identified, which account for approximately 90% of all patients. Type 1 is due to an as yet unidentified gene defect located on chromosome nine. Type 2 is caused by mutations in the perforin (PRF1) gene, type 3 by mutations in the Munc-13-4 (UNC13D) gene, type 4 by mutations in the syntaxin 11 (STX11) gene and the recently described type 5 due to mutations in the gene encoding syntaxin binding protein 2 (STXBP-2). The incidence of the five types varies in different ethnic groups. The most common presenting features are pyrexia of unknown origin, pronounced hepatosplenomegaly and cytopenias. Neurological features tend to present later and are associated with poor prognosis. Absent or decreased lymphocyte cytotoxicity is the cellular hallmark of FHL. Biochemical features such as hyperferritinaemia, hypertriglyceridaemia and hypofibrinogenaemia are usually present, along with high levels of soluble interleukin 2 receptor in the blood and cerebrospinal fluid. Bone marrow aspirate may demonstrate the characteristic haemophagocytes, but initially is non-diagnostic in two-thirds of patients. Established international clinical, haematological and biochemical criteria now facilitate accurate clinical diagnosis. The disease is fatal unless a haematopoietic stem cell transplant (HSCT) is performed. The introduction of HSCT has dramatically improved the prognosis of the disease. However, the mortality of the disease is still significantly high and a number of challenges remain to be addressed. Active disease at the time of the transplant is the major significant poor prognostic factor. Delayed diagnosis, after irreversible organ damage has occurred, especially neurological damage, disease reoccurrence and pre-transplant mortality, remain a concern.

A novel animal model of Epstein-Barr virus-associated hemophagocytic lymphohistiocytosis in humanized mice

EBV-associated hemophagocytic lymphohistiocytosis (EBV-HLH) is a rare yet devastating disorder caused by EBV infection in humans. However, the mechanism of this disease has yet to be elucidated because of a lack of appropriate animal models. Here, we used a human CD34(+) cell-transplanted humanized mouse model and reproduced pathologic conditions resembling EBV-HLH in humans. By 10 weeks postinfection, two-thirds of the infected mice died after exhibiting high and persistent viremia, leukocytosis, IFN-γ cytokinenemia, normocytic anemia, and thrombocytopenia. EBV-infected mice also showed systemic organ infiltration by activated CD8(+) T cells and prominent hemophagocytosis in BM, spleen, and liver. Notably, the level of EBV load in plasma correlated directly with both the activation frequency of CD8(+) T cells and the level of IFN-γ in plasma. Moreover, high levels of EBV-encoded small RNA1 were detected in plasma of infected mice, reflecting what has been observed in patients. These findings suggest that our EBV infection model mirrors virologic, hematologic, and immunopathologic aspects of EBV-HLH. Furthermore, in contrast to CD8(+) T cells, we found a significant decrease of natural killer cells, myeloid dendritic cells, and plasmacytoid dendritic cells in the spleens of infected mice, suggesting that the collapse of balanced immunity associates with the progression of EBV-HLH pathogenesis.

Gene expression profiling of peripheral blood mononuclear cells from children with active hemophagocytic lymphohistiocytosis

Familial hemophagocytic lymphohistiocytosis (FHL) is a rare, genetically heterogeneous autosomal recessive immune disorder that results when the critical regulatory pathways that mediate immune defense mechanisms and the natural termination of immune/inflammatory responses are disrupted or overwhelmed. To advance the understanding of FHL, we performed gene expression profiling of peripheral blood mononuclear cells from 11 children with untreated FHL. Total RNA was isolated and gene expression levels were determined using microarray analysis. Comparisons between patients with FHL and normal pediatric controls (n = 30) identified 915 down-regulated and 550 up-regulated genes with more than or equal to 2.5-fold difference in expression (P ≤ .05). The expression of genes associated with natural killer cell functions, innate and adaptive immune responses, proapoptotic proteins, and B- and T-cell differentiation were down-regulated in patients with FHL. Genes associated with the canonical pathways of interleukin-6 (IL-6), IL-10 IL-1, IL-8, TREM1, LXR/RXR activation, and PPAR signaling and genes encoding of antiapoptotic proteins were overexpressed in patients with FHL. This first study of genome-wide expression profiling in children with FHL demonstrates the complexity of gene expression patterns, which underlie the immunobiology of FHL.

Inherited defects in lymphocyte cytotoxic activity

The granule-dependent cytotoxic activity of lymphocytes plays a critical role in the defense against virally infected cells and tumor cells. The importance of this cytotoxic pathway in immune regulation is evidenced by the severe and often fatal condition, known as hemophagocytic lymphohistiocytic syndrome (HLH) that occurs in mice and humans with genetically determined impaired lymphocyte cytotoxic function. HLH manifests as the occurrence of uncontrolled activation of T lymphocytes and macrophages infiltrating multiple organs. In this review, we focus on recent advances in the characterization of effectors regulating the release of cytotoxic granules, and on the role of this cytotoxic pathway in lymphocyte homeostasis and immune surveillance. Analysis of the mechanisms leading to the occurrence of hemophagocytic syndrome designates gamma-interferon as an attractive therapeutic target to downregulate uncontrolled macrophage activation, which sustains clinical and biological features of HLH.

Sustained IL-4 exposure leads to a novel pathway for hemophagocytosis, inflammation, and tissue macrophage accumulation

Erythrophagocytosis and inflammation from activated macrophages occur in distinct clinical scenarios. The presence of CD8(+) T cells and interferon-γ (IFN-γ) production is required to induce disease in mouse models of hemophagocytic lymphohistiocytosis. We investigated the roles of a different class of proinflammatory cytokines, interleukin-4 (IL-4) and IL-13, in the induction of inflammatory tissue macrophage accumulation and/or hemophagocytosis. We found that large amounts of IL-4, but not IL-13, delivered via an implanted mini-pump or IL-4/anti-IL-4 complexes, lead to substantial YM1(+) tissue macrophage accumulation, erythrophagocytosis within the liver, spleen, and bone marrow, decreased hemoglobin and platelet levels, and acute weight loss. This effect is not dependent on the presence of antibody or T cells, as treatment of Rag2(-/-) mice leads to similar disease, and IFN-γ neutralization during IL-4 treatment had no effect. IL-4 treatment results in suppression of IL-12, elevation of serum IFN-γ, IL-10, and the murine IL-8 homolog KC, but not IL-6, IL-1β, or tumor necrosis factor-α. Finally, mice transgenic for IL-4 production developed tissue macrophage accumulation, disruption of splenic architecture, bone marrow hypocellularity, and extramedullary hematopoiesis. These data describe a novel pathophysiologic pathway for erythrophagocytosis in the context of tissue macrophage accumulation and inflammation involving elevations in IL-4 and alternative macrophage activation.

Spectrum of clinical presentations in familial hemophagocytic lymphohistiocytosis type 5 patients with mutations in STXBP2

Hemophagocytic lymphohistiocytosis (HLH) is an often-fatal hyperinflammatory syndrome characterized by fever, hepatosplenomegaly, cytopenia, and in some cases hemophagocytosis. Here, we describe the mutation analysis, clinical presentation, and functional analysis of natural killer (NK) cells in patients with mutations in STXBP2 encoding Munc18-2, recently associated with familial HLH type 5. The disease severity among 11 persons studied here was highly variable and, accordingly, age at diagnosis ranged from 2 months to 17 years. Remarkably, in addition to typical manifestations of familial HLH (FHL), the clinical findings included colitis, bleeding disorders, and hypogammaglobulinemia in approximately one-third of the patients. Laboratory analysis revealed impairment of NK-cell degranulation and cytotoxic capacity. Interleukin-2 stimulation of lymphocytes in vitro rescued the NK cell-associated functional defects. In conclusion, familial HLH type 5 is associated with a spectrum of clinical symptoms, which may be a reflection of impaired expression and function of Munc18-2 also in cells other than cytotoxic lymphocytes. Mutations in STXBP2 should thus also be considered in patients with clinical manifestations other than those typically associated with HLH.

Reactive haemophagocytic syndrome in 58 HIV-1-infected patients: clinical features, underlying diseases and prognosis

OBJECTIVE

To describe features of reactive haemophagocytic syndrome (RHS) in HIV-1-infected adult patients. To compare characteristics of patients with malignancy-associated RHS and infection-associated RHS.

DESIGN AND SETTING

Retrospective study in three departments of Infectious Diseases/Internal Medicine at three French tertiary centres.

PATIENTS AND METHODS

Medical charts of HIV-1-infected adult patients and RHS seen between January 2006 and December 2007 were reviewed. Demographic, clinical and laboratory data obtained at the time of RHS episode were compared between patients with malignancy-associated RHS and infection-associated RHS using non-parametric tests. The overall survival was assessed using the Kaplan-Meier method.

RESULTS

Fifty-eight HIV-1-infected patients were diagnosed with RHS [certain RHS n = 43, possible RHS n = 15, median (range) age 42 (23-85) years, men 76%]. At time of RHS, the median duration of HIV infection was 4 (0-22) years and 57% received HAART. The median CD4 lymphocyte count was 91 (2-387)/microl and 35% of patients had a plasma HIV-1 RNA less than 50 copies/ml. Underlying haemopathy/malignancy (Hodgkin lymphoma n = 10) or infection (tuberculosis n = 9, cytomegalovirus infection n = 5) were evidenced for 31 and 23 patients, respectively. Patients with haemopathy/malignancy-associated RHS presented more frequently with splenomegaly (97 vs. 70%, P < 0.01), lower aspartate aminotransferase (36 vs. 84 UI/l, P < 0.01) and lactate dehydrogenase (530 vs. 911 UI/l, P < 0.01) levels and CD8 cell count (234 vs. 588/microl, P < 0.01). Eighteen (31%) patients died. The overall survival was not statistically different between the two groups (P = 0.68).

CONCLUSION

In the HAART era, RHS is frequently associated with underlying haemopathy/malignancy, especially Hodgkin lymphoma. The prognosis remains poor but seems, however, better than in the pre-HAART era.

Neutralization of IFNgamma defeats haemophagocytosis in LCMV-infected perforin- and Rab27a-deficient mice

Hereditary haemophagocytic lymphohistiocytosis (HLH) is a fatal inflammatory disease and treatments currently may lead to serious side effects. There is a pressing need for effective, less toxic treatments for this disease. Previous reports have suggested that interferon γ (IFNγ) has a role in the pathogenesis of HLH. Here, we report that blocking IFNγ had a therapeutic effect in two different murine models of human hereditary HLH (perforin-deficient and Rab27a-deficient mice, both infected with lymphocytic choriomeningitis virus). Therapeutic administration of an anti-IFNγ antibody induced recovery from haemophagocytosis in both genetic models, as evidenced by increased survival in perforin-deficient mice and correction of blood cytopenia, moderation of body temperature changes, decreased cytokinaemia, restoration of splenic architecture and reduced haemophagocytosis in the liver of both murine models. Involvement of the central nervous system in Rab27a-deficient mice was prevented by anti-IFNγ therapy. Hepatic T-cell infiltrates and virus persisted, with no detectable harm during the time course of these studies. These data strongly suggest that neutralization of IFNγ could be used in humans to safely alleviate the clinical manifestations of haemophagocytosis.

Gamma(c) deficiency precludes CD8+ T cell memory despite formation of potent T cell effectors

Several cytokines (including IL-2, IL-7, IL-15, and IL-21) that signal through receptors sharing the common gamma chain (gamma(c)) are critical for the generation and peripheral homeostasis of naive and memory T cells. Recently, we demonstrated that effector functions fail to develop in CD4(+) T cells that differentiate in the absence of gamma(c). To assess the role of gamma(c) cytokines in cell-fate decisions that condition effector versus memory CD8(+) T cell generation, we compared the response of CD8(+) T cells from gamma(c)(+) or gamma(c)(-) P14 TCR transgenic mice after challenge with lymphocytic choriomeningitis virus. The intrinsic IL-7-dependent survival defect of gamma(c)(-) naive CD8(+) T cells was corrected by transgenic expression of human Bcl-2. We demonstrated that although gamma(c)-dependent signals are dispensable for the initial expansion and the acquisition of cytotoxic functions following antigenic stimulation, they condition the terminal proliferation and differentiation of CD8(+) effector T cells (i.e., KLRG1(high) CD127(low) short-lived effector T cells) via the transcription factor, T-bet. Moreover, the gamma(c)-dependent signals that are critical for memory T cell formation are not rescued by Bcl2 overexpression. Together, these data reveal an unexpected divergence in the requirement for gamma(c) cytokines in the differentiation of CD4(+) versus CD8(+) cytotoxic T lymphocytes.

Here today--not gone tomorrow: roles for activating receptors in sustaining NK cells during viral infections

The conclusive evidence supporting a role for NK cells in defense against viruses has been obtained under conditions of NK cell deficiencies prior to infections. NK cell proliferation can be induced during infections, but the advantages of resulting expansion have been unclear because NK cell basal frequency is already high. However, NK cell decreases are also observed during certain conditions of viral infection. Given the range of potent antiviral and immunoregulatory functions of NK cells, such "disappearance" dramatically changes the resources available to the host. New studies demonstrate that proliferation dependent on activating receptors for virus-induced ligands is key for NK cell maintenance, and allows their continued availability for control of adaptive immune responses and immunopathology. This pathway for sustaining NK cells may represent a system used generally to select subsets for rescue during homeostatic purging. In the case of NK cells, though, nonselection limits continued access to the many beneficial functions of NK cells. The observations resolve the long-standing conundrum of reported NK cell increases and decreases during viral infections. Moreover, they demonstrate a previously unappreciated role for activating receptors, i.e. to keep NK cells here today and also tomorrow.

Chronic murine typhoid fever is a natural model of secondary hemophagocytic lymphohistiocytosis

Hemophagocytic lymphohistiocytosis (HLH) is a hyper-inflammatory clinical syndrome associated with neoplastic disorders especially lymphoma, autoimmune conditions, and infectious agents including bacteria, viruses, protozoa and fungi. In both human and veterinary medicine, hemophagocytic histiocytic disorders are clinically important and frequently fatal. HLH in humans can be a primary (familial, autosomal recessive) or secondary (acquired) condition, with both types generally precipitated by an infectious agent. Previously, no mouse model for secondary HLH has been reported. Using Salmonella enterica serotype Typhimurium by oral gavage to mimic naturally-occurring infection in Sv129S6 mice, we characterized the clinical, hematologic and morphologic host responses to disease thereby describing an animal model with the clinico-pathologic features of secondary HLH as set forth by the Histiocyte Society: fever, splenomegaly, cytopenias (anemia, thrombocytopenia), hemophagocytosis in bone marrow and spleen, hyperferritinemia, and hypofibrinogenemia. Disease severity correlates with high splenic and hepatic bacterial load, and we show disease course can be monitored and tracked in live animals. Whereby secondary HLH is known to occur in human patients with typhoid fever and other infectious diseases, our characterization of a viable natural disease model of secondary HLH offers an important means to elucidate pathogenesis of poorly understood mechanisms of secondary HLH and investigation of novel therapies. We characterize previously unreported secondary HLH in a chronic mouse model of typhoid fever, and novel changes in hematology including decreased tissue ferric iron storage that differs from classically described anemia of chronic disease. Our studies demonstrate S. Typhimurium infection of mice is a natural infectious disease model of secondary HLH that may have utility for elucidating disease pathogenesis and developing novel therapies.

Hematopoietic stem cell transplantation for familial hemophagocytic lymphohistiocytosis and Epstein-Barr virus-associated hemophagocytic lymphohistiocytosis in Japan

BACKGROUND

Post-transplant outcomes of hemophagocytic lymphohistiocytosis (HLH) patients were analyzed in Japan where Epstein-Barr virus (EBV)-associated severe forms are problematic.

METHODS

Fifty-seven patients (43 familial HLH [12 FHL2, 11 FHL3, 20 undefined], 14 EBV-HLH) who underwent stem cell transplantation (SCT) between 1995 and 2005 were enrolled based on the nationwide registration.

RESULTS

Fifty-seven patients underwent 61 SCTs, including 4 consecutive SCTs. SCTs were employed using allogeneic donors in 93% of cases (allo 53, twin 1, auto 3). Unrelated donor cord blood transplantation (UCBT) was employed in half of cases (21 FHL, 7 EBV-HLH). Reduced intensity conditioning was used in 26% of cases. The 10-year overall survival rates (median +/- SE%) were 65.0 +/- 7.9% in FHL and 85.7 +/- 9.4% in EBV-HLH patients, respectively. The survival of UCBT recipients was >65% in both FHL and EBV-HLH patients. Three out of four patients were alive with successful engraftment after second UCBT. FHL patients showed a poorer outcome due to early treatment-related deaths (<100 days, seven patients) and a higher incidence of sequelae than EBV-HLH patients (P = 0.02). The risk of death for FHL patients having received an unrelated donor bone marrow transplant was marginally higher than that for a related donor SCT (P = 0.05) and that for UCBT (P = 0.07).

CONCLUSIONS

EBV-HLH patients had a better prognosis after SCT than FHL patients. FHL patients showed either an equal or better outcome even after UCBT compared with the recent reports. UCB might therefore be acceptable as an alternate SCT source for HLH patients, although the optimal conditioning remains to be determined.

Mice with a selective impairment of IFN-gamma signaling in macrophage lineage cells demonstrate the critical role of IFN-gamma-activated macrophages for the control of protozoan parasitic infections in vivo

IFN-gamma has long been recognized as a cytokine with potent and varied effects in the immune response. Although its effects on specific cell types have been well studied in vitro, its in vivo effects are less clearly understood because of its diverse actions on many different cell types. Although control of multiple protozoan parasites is thought to depend critically on the direct action of IFN-gamma on macrophages, this premise has never been directly proven in vivo. To more directly examine the effects of IFN-gamma on cells of the macrophage lineage in vivo, we generated mice called the "macrophages insensitive to IFN-gamma" (MIIG) mice, which express a dominant negative mutant IFN-gamma receptor in CD68+ cells: monocytes, macrophages, dendritic cells, and mast cells. Macrophage lineage cells and mast cells from these mice are unable to respond to IFN-gamma, whereas other cells are able to produce and respond to this cytokine normally. When challenged in vitro, macrophages from MIIG mice were unable produce NO or kill Trypanosoma cruzi or Leishmania major after priming with IFN-gamma. Furthermore, MIIG mice demonstrated impaired parasite control and heightened mortality after T. cruzi, L. major, and Toxoplasma gondii infection, despite an appropriate IFN-gamma response. In contrast, MIIG mice displayed normal control of lymphocytic choriomeningitis virus, despite persistent insensitivity of macrophages to IFN-gamma. Thus, the MIIG mouse formally demonstrates for the first time in vivo, the specific importance of direct, IFN-gamma mediated activation of macrophages for controlling infection with multiple protozoan parasites.

Perforin deficiency and susceptibility to cancer

Cytotoxic lymphocytes (CLs) are the killer cells that destroy intracellular pathogen-infected and transformed cells, predominantly through the cytotoxic granule-mediated death pathway. Soluble cytotoxic granule components, including pore-forming perforin and pro-apoptotic serine proteases, granzymes, synergize to induce unscheduled apoptosis of the target cell. A complete loss of CL function results in an aggressive immunoregulatory disorder, familial hemophagocytic lymphohistiocytosis, whereas a partial loss of function seems to be a factor strongly predisposing to hematological malignancies. This review discusses the pathological manifestations of CL deficiencies due to impaired perforin function and describes novel aspects of perforin biology.

Failure of interferon gamma to induce the anti-inflammatory interleukin 18 binding protein in familial hemophagocytosis

Background

Familial hemophagocytosis (FHL) is a rare disease associated with defects in proteins involved in CD8⁺ T-cell cytotoxicity. Hyperactivation of immune cells results in a perilous, Th1-driven cytokine storm. We set out to explore the regulation of cytokines in an FHL patient who was clinically stable on low-dose immunosuppressive therapy after bone marrow transplantation over a six-month period. During this period, chimerism analyses showed that the fraction of host cells was between 1 and 10%. Both parents of the patient as well as healthy volunteers were studied for comparison.

Methods/Principal Findings

Using ELISA, quantitative real-time PCR, and clinical laboratory methods, we investigated constitutive and inducible cytokines, polymorphisms, and clinical parameters in whole blood and whole blood cultures. Although routine laboratory tests were within the normal range, the chemokines IP-10 and IL-8 as well as the cytokine IL-27p28 were increased up to 10-fold under constitutive and stimulated conditions compared to healthy controls. Moreover, high levels of IFNγ and TNFα were produced upon stimulation. Unexpectedly, IFNγ induction of IL-18 binding protein (IL-18BP) was markedly reduced (1.6-fold vs 5-fold in controls). The patient's mother featured intermediately increased cytokine levels, whereas levels in the father were similar to those in the controls.

Conclusions/Significance

Since IL-18 plays a major role in perpetuating hemophagocytosis, the failure of IFNγ to induce IL-18BP may constitute a fundamental pathogenetic mechanism. Furthermore, increased production of IL-8 and IL-27 appears to be associated with this disease. Such dysregulation of cytokines was also found in the heterozygous parents, providing a novel insight into genotype-phenotype correlation of FHL which may encourage future research of this rare disease.

Delayed addition of tumor necrosis factor (TNF) antagonists inhibits the generation of CD11c+ dendritic cells derived from CD34+ cells exposed to TNF-alpha

We have developed a method that cells exhibiting typical dendritic cell (DC) characteristics are generated from human CD34(+) cells and phagocytose cogenerating erythroid progenitor cells in the presence of tumor necrosis factor-alpha (TNF-alpha), interleukin-3, stem cell factor and erythropoietin. Using this system, we titrated the effects of TNF antagonists, etanercept and infliximab, on TNF-alpha activity. We found that 1 microg/ml etanercept dramatically inhibited the generation of CD11c(+) cells accompanying with a complete recovery of the generation of erythroid progenitors. Infliximab at 200 microg/ml exhibited a similar effect to that observed for etanercept. The delayed addition of etanercept to this culture system at day five resulted in significant inhibitory effects on the generation of CD11c(+), CD4(+) and CD86(+) cells. These results indicate that TNF antagonists administered at a concentration that is achievable in vivo, neutralize the biologic effects of TNF-alpha in generating CD11c(+) cells and that a delay in the administration of these antagonists for as long as 5 days partially inhibits the biologic activity of TNF-alpha. These findings may contribute to a great understanding of anti-TNF therapy in patients with an overproduction of cytokines such as hemophagocytic syndromes.

Integrating WHO 2001-2008 criteria for the diagnosis of Myelodysplastic Syndrome (MDS): a case-case analysis of benzene exposure

We characterized the prevalence of hematopoietic and lymphoid disease for 2923 consecutive patients presenting at 29 hospitals from August 2003 to June 2007. Diagnoses were made in our laboratory using WHO criteria based on morphologic, immunophenotypic, cytogenetic, FISH and molecular data. A total of 611 subjects (322 males/289 females) were prospectively diagnosed with MDS using WHO (2001) criteria. Update and re-evaluation of cases using MDS (2008) criteria resulted in 649 MDS cases. Using WHO (2008) criteria, refractory cytopenia with multilineage dysplasia (RCMD) accounted for 68% of total cases, refractory anemia with excess blasts (RAEB), 16.3%; refractory anemia (RA), 6.5%; refractory cytopenia with unilineage dysplasia (RCUD), 4%; and MDS-unclassifiable (MDS-U), 4.5%. Subjects were administered questionnaires and information on previous disease, work histories and exposures to potential etiologic agents such as benzene (BZ) was obtained. A total of 80/649 (13.2%) were determined to have some BZ exposure. The frequency of clonal cytogenetic abnormalities in all MDS was 30%, the most common being +8>del(20)q>del(7q)>del(5q), while the analogous frequency in BZ-exposed cases was only 24%. To further investigate the characteristics of MDS associated with BZ, we identified a subset of cases with high BZ exposure. These BZ signal cases were each matched by age and gender to two cases with no known BZ exposure. When contrasting BZ signal cases vs matched cases with no BZ exposure, we found a high odds ratio (OR) for the WHO subtype MDS-U (OR=11.1), followed by RAEB and RCUD (OR=1), RA (OR=0.7) and RCMD (OR=0.6). Multilineage dysplasia with abnormal eosinophils (MDS-Eo) was strongly associated with BZ exposure, whereas the relative risk of clonal cytogenetic abnormalities was reduced for high BZ-exposed cases (OR=0.5). These findings are strongly indicative that MDS subtypes are influenced by BZ exposure, and taken together with previous studies, the features of MDS-Eo suggest that altered immune regulation plays a major role in the pathogenesis of MDS following chronic exposure to BZ.

Munc18-2 deficiency causes familial hemophagocytic lymphohistiocytosis type 5 and impairs cytotoxic granule exocytosis in patient NK cells

Familial hemophagocytic lymphohistiocytosis (FHL) is a genetically heterogeneous autosomal recessive immune disorder characterized by the occurrence of uncontrolled activation of lymphocytes and macrophages infiltrating multiple organs. Disease-causing mutations in the perforin (PRF1; also known as FHL2), Munc13-4 (UNC13D; also known as FHL3), and syntaxin-11 (STX11; also known as FHL4) genes have been identified in individuals with FHL. These genes all encode proteins involved in the cytotoxic activity of lymphocytes. Here, we show that the gene encoding syntaxin-binding protein 2 (Munc18-2; official gene symbol STXBP2) is mutated in another subset of patients with FHL (designated by us as "FHL5"). Lymphoblasts isolated from these patients had strongly decreased STXBP2 protein expression, and NK cells exhibited impaired cytotoxic granule exocytosis, a defect that could be overcome by ectopic expression of wild-type STXBP2. Furthermore, we provide evidence that syntaxin-11 is the main partner of STXBP2 in lymphocytes, as its expression required the presence of STXBP2. Our work shows that STXBP2 deficiency causes FHL5. These data indicate that STXBP2 is required at a late step of the secretory pathway for the release of cytotoxic granules by binding syntaxin 11, another component of the intracellular membrane fusion machinery.

Identification of Mouse Cytomegalovirus Resistance Loci by ENU Mutagenesis

Host resistance to infection depends on the efficiency with which innate immune responses keep the infectious agent in check. Innate immunity encompasses components with sensing, signaling and effector properties. These elements with non-redundant functions are encoded by a set of host genes, the resistome. Here, we review our findings concerning the resistome. We have screened randomly mutagenized mice for susceptibility to a natural opportunistic pathogen, the mouse cytomegalovirus. We found that some genes with initially no obvious functions in innate immunity may be critical for host survival to infections, falling into a newly defined category of genes of the resistome.

Activating receptors promote NK cell expansion for maintenance, IL-10 production, and CD8 T cell regulation during viral infection

Natural killer (NK) cells have the potential to deliver both direct antimicrobial effects and regulate adaptive immune responses, but NK cell yields have been reported to vary greatly during different viral infections. Activating receptors, including the Ly49H molecule recognizing mouse cytomegalovirus (MCMV), can stimulate NK cell expansion. To define Ly49H's role in supporting NK cell proliferation and maintenance under conditions of uncontrolled viral infection, experiments were performed in Ly49h^−/−, perforin 1 (Prf1)^−/−, and wild-type (wt) B6 mice. NK cell numbers were similar in uninfected mice, but relative to responses in MCMV-infected wt mice, NK cell yields declined in the absence of Ly49h and increased in the absence of Prf1, with high rates of proliferation and Ly49H expression on nearly all cells. The expansion was abolished in mice deficient for both Ly49h and Prf1 (Ly49h^−/−Prf1^−/−), and negative consequences for survival were revealed. The Ly49H-dependent protection mechanism delivered in the absence of Prf1 was a result of interleukin 10 production, by the sustained NK cells, to regulate the magnitude of CD8 T cell responses. Thus, the studies demonstrate a previously unappreciated critical role for activating receptors in keeping NK cells present during viral infection to regulate adaptive immune responses.

EBAG9 tempers lymphocyte killing activity

The cytotoxic activity of lymphocytes is crucial for immune surveillance and homeostasis. Several independent, naturally occurring genetic models characterized by defects in granule trafficking or exocytosis have helped to decipher the multiple steps and molecules that regulate the cytotoxic process. The study by Rüder and colleagues in this issue of the JCI shows that an engineered absence of EBAG9, previously reported as a tumor-associated antigen, enhances cytotoxic activity of CTLs but not NK cells, likely acting on the endosomal-lysosomal trafficking of the cytotoxic effectors (see the related article beginning on page 2184). This finding adds a new piece to the puzzle of complex mechanisms that tightly regulate the capacity of the cytotoxic response and suggests a new target to negatively modulate CTL responsiveness.

Characteristics of hemophagocytic lymphohistiocytosis in neonates: a nationwide survey in Japan

OBJECTIVE

To assess the etiology, prognosis, and appropriate treatment of hemophagocytic lymphohistiocytosis (HLH) in neonates.

STUDY DESIGN

We collected information on neonates in whom HLH was diagnosed between 1997 and 2007 from participating members of the Japanese Society of Pediatric Hematology.

RESULTS

HLH was diagnosed in 20 patients within 4 weeks after birth. Of the diagnostic criteria for HLH-2004, the incidence of fever was quite low in preterm infants, and hypertriglyceridemia and neutropenia were uncommon. Familial HLH (n = 6) or severe combined immunodeficiency-associated HLH (n = 1) was diagnosed in 7 patients, and 2 of them have survived. Herpes simplex virus-associated HLH was diagnosed in 6 patients, and 2 of them have survived. The overall survival rate for the 20 patients was 40%.

CONCLUSIONS

HLH is rare in neonates and has a poor prognosis. Early diagnosis and immediate treatment are required when considering the possibility of herpes simplex virus-associated or familial HLH.

Crosstalk between components of the innate immune system: promoting anti-microbial defenses and avoiding immunopathologies

Because it reaches full functional efficacy rapidly upon encounter with a pathogen, the innate immune system is considered as the first line of defense against infections. The sensing of microbes or of transformed or infected cells, through innate immune recognition receptors (referred to as activating I2R2), initiates pro-inflammatory responses and innate immune effector functions. Other I2R2 with inhibitory properties bind self-ligands constitutively expressed in host. However, this dichotomy in the recognition of foreign or induced self versus constitutive self by I2R2 is not always respected in certain non-infectious conditions reminiscent of immunopathologies. In this review, we discuss that immune mechanisms have evolved to avoid inappropriate inflammatory disorders in individuals. Molecular crossregulation exists between components of I2R2 signaling pathways, and intricate interactions between cells from both innate and adaptive immune systems set the bases of controlled immune responses. We also pinpoint that, like T or B cells, some cells of the innate immune system must go through education processes to prevent autoreactivity. In addition, we illustrate how gene expression profiling of immune cell types is a useful tool to find functional homologies between cell subsets of different species and to speculate about unidentified functions of these cells in the responses to pathogen infections.

Haemophagocytic syndrome and HIV

PURPOSE OF REVIEW

Haemophagocytic syndrome (HPS) is a relatively rare complication of HIV infection but one that can take a particularly aggressive and potentially fatal course. The condition may be underrecognized due to the nonspecific nature of the clinical features. This review summarizes the pathogenesis, clinical and diagnostic features, common associations and current options in the management of HPS in the context of HIV infection, with the aim of increasing diagnostic awareness and facilitating early intervention.

RECENT FINDINGS

Our understanding of HPS is being increasingly informed by research into the molecular basis of the familial forms of the condition. The list of associated infections and neoplasms continues to lengthen, although the occurrence of HPS is increasingly recognized in the context of HIV infection alone, occasionally as its initial presentation in acute seroconversion. Diagnostic guidelines have recently been refined and attempts to adapt these to particular patient groups are ongoing. Management of HIV-associated HPS is adapted to the clinical context and may involve treatment of an underlying disorder or immunosuppressive therapy to reduce the activation of macrophages and T cells.

SUMMARY

The spectrum of HIV-related lymphoproliferative disorders continues to expand. Our understanding of their molecular and cellular basis and the role of infectious organisms in their development increasingly shapes and advances our clinical management of these complex conditions.

STAT3 transcription factor is constitutively activated and is oncogenic in nasal-type NK/T-cell lymphoma

Nasal-type natural killer (NK) cell lymphoma is an infrequent aggressive malignant disease with very poor prognosis. We aimed to explore the possible role of the transcription factor STAT3 in the pathophysiology of this malignancy, as it was involved in oncogenesis and chemoresistance. For this, we established and characterized a continuous interleukin 2-dependent NK cell line (MEC04) from a patient with a fatal nasal-type NK-cell lymphoma. Cells harbored poor cytotoxic activity against K562 cells, and spontaneously secreted interferon-gamma, interleukin-10 and vascular-endothelium growth factor in vitro. STAT3 was phosphorylated in Y705 dimerization residue in MEC04 cells and restricted to the nucleus. Y705 STAT3 phosphorylation involved JAK2, as exposure of cells to AG490 inhibitor inhibited Y705 STAT3 phosphorylation. By using recombinant transducible TAT-STAT3-beta (beta isoform), TAT-STAT3Y705F (a STAT3 protein mutated on Y705 residue, which prevents STAT3 dimerization) and peptides inhibiting specifically STAT3 dimerization, we inhibited STAT3 phosphorylation and cell growth, with cell death induction. Finally, STAT3 was phosphorylated in Y705 residue in the nuclei of lymphoma cells in eight/nine patients with nasal-type NK/T-cell lymphoma and in YT, another NK cell line. Our results suggest that STAT3 protein has a major role in the oncogenic process of nasal-type NK-cell lymphomas, and may represent a promising therapeutical target.

Macrophage activation syndrome: serological markers and treatment with anti-thymocyte globulin

Two patients presented at the University of Rochester Medical Center with a febrile illness, cytopenias, organ failure (liver failure or respiratory failure), and markedly elevated serum ferritin and sIL-2R. A diagnosis of probable macrophage activation syndrome was made. Both patients failed initial therapy with steroids and cyclosporine, either due to toxicity or lack of efficacy. Both patients responded dramatically to rabbit anti-thymocyte globulin (ATG).

Key role of macrophages in the pathogenesis of CD18 hypomorphic murine model of psoriasis

Psoriasis is a chronic skin disorder of unsolved pathogenesis affecting skin in 2-3% of the general population. Research into the pathogenesis of psoriasis has profited from suitable animal models. Previously, we reported on the CD18 hypomorphic (CD18(hypo)) PL/J mouse model clinically resembling human psoriasis, which is characterized by reduced expression of the common chain of beta(2)-integrins (CD11/CD18) to only 2-16% of wild-type levels. Aside from common clinical and pathophysiological features shared with human psoriasis, the psoriasiform skin disease in CD18(hypo) PL/J mice also depends on the presence of CD4(+) T-cells. This review focuses on the role of activated macrophages in the pathogenesis of CD18(hypo) T-cell-mediated mouse model of psoriasis, and extends our understanding in unrestrained pathogenic T-cells whose activation may be crucial for the recruitment and activation of macrophages within skin. The findings in the CD18(hypo) PL/J model are discussed in the context of current literatures of human and other autoimmune disorders.

Perforin-mediated suppression of B-cell lymphoma

In the present study, we have examined the effect of perforin (pfp) deficiency in 4 models of mouse B-cell lymphomagenesis. We have examined pfp loss on the background of either Mlh1 tumor suppressor allele loss or oncogene expression [Ig heavy chain (Emu)-v-Abl, Emu-myc, and vav-bcl2]. Pfp was shown to act as a suppressor of B-cell malignancies characteristically driven by v-Abl or bcl-2, whereas Mlh loss cooperated in accelerating spontaneous B-cell lymphomas characteristic of pfp loss. No protective role for pfp was observed in the more aggressive Emu-myc model of B-cell lymphoma. These transgenic models have allowed us to distinguish the role of pfp in surveillance of B-cell lymphomagenesis, as opposed to its loss simply driving the onset of a spontaneous lymphoma characteristic of pfp deficiency.

Mice lacking asparaginyl endopeptidase develop disorders resembling hemophagocytic syndrome

Asparaginyl endopeptidase (AEP or legumain) is a lysosomal cysteine protease that cleaves protein substrates on the C-terminal side of asparagine. AEP plays a pivotal role in the endosome/lysosomal degradation system and is implicated in antigen processing. The processing of the lysosomal proteases cathepsins in kidney is completely defective in AEP-deficient mice with accumulation of macromolecules in the lysosomes, which is typically seen in lysosomal disorders. Here we show that mutant mice lacking AEP develop fever, cytopenia, hepatosplenomegaly, and hemophagocytosis, which are primary pathological manifestations of hemophagocytic syndrome/hemophagocytic lymphohistiocytosis (HLH). Moreover, AEP deficiency provokes extramedullary hematopoiesis in the spleen and abnormally enlarged histiocytes with ingested red blood cells (RBCs) in bone marrow. Interestingly, RBCs from AEP-null mice are defective in plasma membrane components. Further, AEP-null mice display lower natural killer cell activity, but none of the major cytokines is substantially abnormal. These results indicate that AEP might be a previously unrecognized component in HLH pathophysiology.

Functional assessment of perforin C2 domain mutations illustrates the critical role for calcium-dependent lipid binding in perforin cytotoxic function

Perforin-mediated lymphocyte cytotoxicity is critical for pathogen elimination and immune homeostasis. Perforin disruption of target cell membranes is hypothesized to require binding of a calcium-dependent, lipid-inserting, C2 domain. In a family affected by hemophagocytic lymphohistiocytosis, a severe inflammatory disorder caused by perforin deficiency, we identified 2 amino acid substitutions in the perforin C2 domain: T435M, a previously identified mutant with disputed pathogenicity, and Y438C, a novel substitution. Using biophysical modeling, we predicted that the T435M substitution, but not Y438C, would interfere with calcium binding and thus cytotoxic function. The capacity for cytotoxic function was tested after expression of the variant perforins in rat basophilic leukemia cells and murine cytotoxic T lymphocytes. As predicted, cells transduced with perforin-T435M lacked cytotoxicity, but those expressing perforin-Y438C displayed intact cytotoxic function. Using novel antibody-capture and liposome-binding assays, we found that both mutant perforins were secreted; however, only nonmutated and Y438C-substituted perforins were capable of calcium-dependent lipid binding. In addition, we found that perforin-Y438C was capable of mediating cytotoxicity without apparent proteolytic maturation. This study clearly demonstrates the pathogenicity of the T435M mutation and illustrates, for the first time, the critical role of the human perforin C2 domain for calcium-dependent, cytotoxic function.

Hemophagocytic lymphohistiocytosis (HLH) and related disorders

Hemophagocytic lymphohistiocytosis (HLH), which has many genetic causes, is characterized by multi-system inflammation. HLH is a reactive process resulting from prolonged and excessive activation of antigen presenting cells (macrophages, histiocytes) and CD8(+) T cells. Hemophagocytosis, which is mediated through the CD163 heme-scavenging receptor, is a hallmark of activated macrophages/histiocytes and is the characteristic finding for which the disorder was named. The majority of genetic causes identified to date affect the cytotoxic function of NK and T cells, crippling immunologic mechanisms that mediate natural immune contraction. The predominant clinical findings of HLH are fevers (often hectic and persistent), cytopenias, hepatitis and splenomegaly. Due to the life-threatening implications of the diagnosis of genetically determined HLH, antiinflammatory therapy, often consisting of steroids, etoposide or antithymocyte globulin (ATG), should be instituted promptly, followed by curative hematopoietic cell transplantation. Secondary HLH, associated with autoimmune disorders or viral infections in teens and adults, also carries a significant mortality rate and should be managed in consultation with specialists familiar with the diagnosis and treatment of such disorders.

Analysis of triglyceride value in the diagnosis and treatment response of secondary hemophagocytic syndrome

BACKGROUND/AIMS

Secondary hemophagocytic syndrome (hemophagocytic lymphohistiocytosis, HLH) follows viral infection, malignant disorders, and autoimmune disease. Criteria for HLH diagnosis, which were proposed in 2004, include hypertriglyceridemia. However, some studies reported the absence of hypertriglyceridemia in patients with secondary HLH, differing from those with primary HLH.

SUBJECTS AND METHODS

In this study, we investigated the presence or absence of hypertriglyceridemia in 28 patients who were diagnosed with secondary HLH between 1997 and 2007 retrospectively. There were no patients undergoing treatment for those with a history of hyperlipidemia.

RESULTS

The subjects consisted of 14 patients with lymphoma-associated HLH, 11 with virus-associated HLH, 2 with autoimmune disease-associated HLH, and 1 with post transplantation HLH. In 19 patients (68%), hypertriglyceridemia was noted on diagnosis or during the disease period (mean: 242 mg/dL). Furthermore, the triglyceride (TG) level decreased with the treatment-related amelioration of HLH (mean level before and after treatment: 297 and 136 mg/dL, respectively, p=0.0001).

CONCLUSION

These results suggest that the TG level is useful for diagnosing HLH and evaluating the treatment response. TG measurement is simple and inexpensive; therefore, this parameter can be determined several times to evaluate the treatment response.

Necrotizing epiglottitis and hemophagocytic lymphohistiocytosis

With the introduction of vaccination for haemophilus influenza, the epidemiology of epiglottitis in children has changed. Classic childhood epiglottitis is now rare, and unusual forms of the disease may be seen. Nectrotizing epiglottitis is an extremely rare form of epiglottitis. Only four cases of nectrotizing epiglottitis have been previously reported, and all cases were in immunocompromised adult patients. Hemophagocytic lymphohistiocytosis is a rare condition characterized by high fevers, hepatosplenomegaly, and cytopenias caused by an abnormal proliferation and activation of macrophages. We report the first case of a previously healthy 5-year-old male presenting with acute onset of airway distress and pancytopenia. Subsequent airway evaluation led to the diagnosis of nectrotizing epiglottitis, and he was simultaneously diagnosed with infection-induced hemophagocytic lymphohistiocytosis. The patient recovered with intubation and antibiotics. Follow-up direct laryngoscopy revealed an epiglottis remnant with approximately 50% loss of epiglottic tissue. The presentation and pathophysiology of this unusual manifestation of epiglottitis and hemophagocytic lymphohistiocytosis will be reviewed. In the post-haemophilus influenze vaccination era, the pediatric otolaryngologist must be familiar with unusual forms of epiglottitis and its associated manifestations.

Microbe sensing, positive feedback loops, and the pathogenesis of inflammatory diseases

The molecular apparatus that protects us against infection can also injure us by causing autoimmune or autoinflammatory disease. It now seems that at times, defects within the sensing arm of innate immunity contribute to diseases of this type. The initiation of an immune response is often microbe dependent and, in many cases, Toll-like receptor (TLR) dependent. Positive feedback loops triggering immune activation may occur when TLR signaling pathways stimulate host cells in an unchecked manner. Or, immune activation may persist because of failure to eradicate an inciting infection. Or on occasion, endogenous DNA may trigger specific immune responses that beget further responses in a TLR-dependent autoamplification loop. Specific biochemical defects that cause loop-related autoimmunity have been revealed by random germline mutagenesis and by gene targeting. We have also developed some insight into critical points at which feedback loops can be interrupted.

Reconstitution inflammatory syndrome related to histoplasmosis, with a hemophagocytic syndrome in HIV infection

Immune reconstitution after initiation of antiretroviral therapy may unmask a latent infection. We report a case of disseminated Histoplasma capsulatum capsulatum infection associated with a hemophagocytic syndrome in an HIV-infected patient, three weeks after initiation of antiretroviral therapy. The immune reconstitution inflammatory syndrome might be a risk factor for hemophagocytosis.

A Griscelli syndrome type 2 murine model of hemophagocytic lymphohistiocytosis (HLH)

Griscelli syndrome type 2 is caused by mutations in the RAB27A gene and is a rare and potentially fatal immune disorder associated with hemophagocytic lymphohistiocytosis (HLH). Animal models could provide assistance for better understanding the mechanisms and finding new treatments. Rab27a-deficient (ashen) mice do not spontaneously develop HLH. When injected with lymphocytic choriomeningitis virus (LCMV) strain WE, Rab27a-deficient C57BL/6 mice developed wasting disease, hypothermia, splenomegaly, cytopenia (anemia, neutropenia and thrombocytopenia), hypertriglyceridemia and increased levels of IFN-gamma, TNF-alpha, GM-CSF, IL-12, CCL5 and IL-10. Activated macrophages with hemophagocytosis were found in liver sections of these mice. Compared with perforin-deficient mice, LCMV-infected Rab27a-deficient mice showed a substantially better survival rate and slightly higher viral doses were needed to trigger HLH in Rab27a-deficient mice. This study demonstrates that LCMV-infected Rab27a-deficient C57BL/6 mice develop features consistent with HLH and, therefore, represent a murine model of HLH in human Griscelli syndrome type 2.

Intracellular microbes and haemophagocytosis

Haemophagocytosis (hemophagocytosis) is the phenomenon of activated macrophage consumption of red and white blood cells, including professional phagocytes and lymphocytes. It can occur in patients with severe cases of intracellular microbial infection, including avian influenza, leishmaniasis, tuberculosis and typhoid fever. While well-known to physicians since at least the mid-1800s, haemophagocytosis has been little studied due to a paucity of tractable animal and cell culture models. Recently, haemophagocytosis has been described in a mouse model of typhoid fever, and it was noted that the infectious agent, Salmonella enterica, resides within haemophagocytic macrophages in mice. In addition, a cell culture model for haemophagocytosis revealed that S. enterica preferentially replicate in haemophagocytic macrophages. This review describes how, at the molecular and cellular levels, S. enterica may promote and take advantage of haemophagocytosis to establish long-term systemic infections in mammals. The role, relevance and possible molecular mechanisms of haemophagocytosis are discussed within the context of other microbial infections and of genetic deficiencies in which haemophagocytosis occurs and is associated with morbidity.

Inflammation and autoimmunity caused by a SHP1 mutation depend on IL-1, MyD88, and a microbial trigger

A recessive phenotype called spin (spontaneous inflammation) was induced by N-ethyl-N-nitrosourea (ENU) mutagenesis in C57BL/6J mice. Homozygotes display chronic inflammatory lesions affecting the feet, salivary glands and lungs, and antichromatin antibodies. They are immunocompetent and show enhanced resistance to infection by Listeria monocytogenes. TLR-induced TNF and IL-1 production are normal in macrophages derived from spin mice. The autoinflammatory phenotype of spin mice is fully suppressed by compound homozygosity for Myd88(poc), Irak4(otiose), and Il1r1-null mutations, but not Ticam1(Lps2), Stat1(m1Btlr), or Tnf-null mutations. Both autoimmune and autoinflammatory phenotypes are suppressed when spin homozygotes are derived into a germ-free environment. The spin phenotype was ascribed to a viable hypomorphic allele of Ptpn6, which encodes the tyrosine phosphatase SHP1, mutated in mice with the classical motheaten alleles me and me-v. Inflammation and autoimmunity caused by SHP1 deficiency are thus conditional. The SHP1-deficient phenotype is driven by microbes, which activate TLR signaling pathways to elicit IL-1 production. IL-1 signaling via MyD88 elicits inflammatory disease.

Hemophagocytic lymphohistiocytosis and other hemophagocytic disorders

Hemophagocytic disorders result when critical regulatory pathways responsible for the natural termination of immune/inflammatory responses are disrupted or overwhelmed. Hemophagocytic disorders reflect pathologic defects that alter the normal crosstalk between innate and adaptive immune responses, and compromise homeostatic removal of cells that are superfluous or dangerous to the organism. Although hemophagocytic disorders are considered rare, increased awareness of these conditions has led to more frequent diagnoses, more rapid initiation of life-saving treatments, and new insights into the molecules and pathways involved in natural immune down-regulation. Furthermore, improved understanding of the immunologic abnormalities revealed by hemophagocytic disorders informs potential new treatments for life-threatening multisystem organ dysfunction related to sepsis in the intensive care unit setting and severe cases.

Hematopoietic cell transplantation for hemophagocytic lymphohistiocytosis: a journey of a thousand miles begins with a single (big) step

Hemophagocytic lymphohistiocytosis (HLH) is a rare, highly fatal disorder of uncontrolled inflammation, usually affecting infants. Significant progress in the treatment of this disorder has been achieved during the last decade, and outcomes for larger series of patients have been reported in recent years. Although medical therapy has advanced, hematopoietic cell transplantation remains the only curative therapy for patients with the familial form of this disorder. Unfortunately, these patients have demonstrated relatively poor post-transplant outcomes for a nonmalignant disorder, with approximately 30% mortality in the first 100 days. Early deaths were attributable to infection, GVHD, and unusually high rates of primary nonengraftment, venoocclusive disease and pneumonitis. In addition, a significant number of deaths were due to HLH reactivation, a unique complication seen in this patient group. In contrast, late complications were relatively infrequent and essentially all patients with durable engraftment remained in remission indefinitely. In this review, we will discuss recent progress in the transplant management of patients with HLH and potential future strategies, including the use of reduced intensity conditioning regimens.

Early diagnostic and prognostic significance of a specific Th1/Th2 cytokine pattern in children with haemophagocytic syndrome

The haemophagocytic syndrome (HPS) is a rare but frequently fatal disorder of immune regulation caused by hypercytokinemia. Using cytometric bead array technique, the serum T-helper cell type 1 (Th1) and 2 (Th2) cytokines including interferon-gamma (IFN-gamma), tumour necrosis factor (TNF), interleukin (IL)-10, IL-6, IL-4 and IL-2 were determined in 24 children with de novo HPS and 87 children as control. The median levels of serum IFN-gamma, IL-10 and IL-6 in the acute phase of HPS were 901.7, 879.0 and 63.8 pg/ml, respectively, significantly higher than those after remission, and in the healthy volunteers and patients with viral infection. IL-4 was slightly elevated while IL-2 and TNF were within normal range in acute phase. Patients with bacterial sepsis showed an extremely high level of IL-6 and moderate level of IL-10, whereas IFN-gamma was only slightly elevated. Five patients were diagnosed with HPS according to the Th1/Th2 cytokine pattern 3-13 d earlier than they fulfilled the relevant diagnostic criteria. IL-10 level >2000 pg/ml was an unfavorable prognostic factor for HPS treatment response (P = 0.033) and outcome (P = 0.009). We conclude that the significant increase of IFN-gamma and IL-10 and a slightly increased level of IL-6 is an early, specific and prognostic cytokine pattern for childhood HPS.