Patients and mice with deficiency in the SNARE protein SYNTAXIN-11 have a secondary B cell defect.

SYNTAXIN-11 (STX11) is a SNARE protein that mediates the fusion of cytotoxic granules with the plasma membrane at the immunological synapses of CD8 T or NK cells. Autosomal recessive inheritance of deleterious STX11 variants impairs cytotoxic granule exocytosis, causing familial hemophagocytic lymphohistiocytosis type 4 (FHL-4). In several FHL-4 patients, we also observed hypogammaglobulinemia, elevated frequencies of naive B cells, and increased double-negative DN2:DN1 B cell ratios, indicating a hitherto unrecognized role of STX11 in humoral immunity. Detailed analysis of Stx11-deficient mice revealed impaired CD4 T cell help for B cells, associated with disrupted germinal center formation, reduced isotype class switching, and low antibody avidity. Mechanistically, Stx11-/- CD4 T cells exhibit impaired membrane fusion leading to reduced CD107a and CD40L surface mobilization and diminished IL-2 and IL-10 secretion. Our findings highlight a critical role of STX11 in SNARE-mediated membrane trafficking and vesicle exocytosis in CD4 T cells, important for successful CD4 T cell-B cell interactions. Deficiency in STX11 impairs CD4 T cell-dependent B cell differentiation and humoral responses.

Macrophage depletion using clodronate liposomes reveals latent dysfunction of the hematopoietic microenvironment associated with persistently imbalanced M1/M2 macrophage polarization in a mouse model of hemophagocytic lymphohistiocytosis.

Hemophagocytic lymphohistiocytosis (HLH), a hyperinflammatory syndrome, is caused by the incessant activation of lymphocytes and macrophages, resulting in damage to organs, including hematopoietic organs. Recently, we demonstrated that repeated lipopolysaccharide (LPS) treatment induces HLH-like features in senescence-accelerated (SAMP1/TA-1) mice but not in senescence-resistant control (SAMR1) mice. Hematopoietic failure in LPS-treated SAMP1/TA-1 mice was attributed to hematopoietic microenvironment dysfunction, concomitant with severely imbalanced M1 and M2 macrophage polarization. Macrophages are a major component of the bone marrow (BM) hematopoietic microenvironment. Clodronate liposomes are useful tools for in vivo macrophage depletion. In this study, we depleted macrophages using clodronate liposomes to determine their role in the hematopoietic microenvironment in SAMP1/TA-1 and SAMR1 mice. Under clodronate liposome treatment, the response between SAMR1 and SAMP1/TA-1 mice differed as follows: (1) increase in the number of activated M1 and M2 macrophages derived from newly generated macrophages and M2-dominant and imbalanced M1 and M2 macrophage polarization in the BM and spleen; (2) severe anemia and thrombocytopenia; (3) high mortality rate; (4) decrease in erythroid progenitors and B cell progenitors in the BM; and (5) decrease in the mRNA expression of erythroid-positive regulators such as erythropoietin and increase in that of erythroid- and B lymphoid-negative regulators such as interferon-γ in the BM. Depletion of residual macrophages in SAMP1/TA-1 mice impaired hematopoietic homeostasis, particularly erythropoiesis and B lymphopoiesis, owing to functional impairment of the hematopoietic microenvironment accompanied by persistently imbalanced M1/M2 polarization. Thus, macrophages play a vital role in regulating the hematopoietic microenvironment to maintain homeostasis.

Soluble Trem2 is a negative regulator of erythrophagocytosis after intracerebral hemorrhage in a CD36 receptor recycling manner.

INTRODUCTION: Microglia and macrophages participate in hematoma clearance after intracerebral hemorrhage (ICH), thereby facilitating tissue restoration and neurological recovery. Triggering receptor expressed on myeloid cells 2 (Trem2) has been indicated as a major pathology-induced immune signaling hub on the microglial/macrophage surface. Soluble Trem2 (sTrem2), the proteolytic form of Trem2, is abundant in the body fluid and is positively correlated with the pathological process. OBJECTIVES: In the present study, we aimed to investigate the potential role of sTrem2 in hematoma resolution after ICH and to elucidate its underlying mechanisms. METHODS: We explored the biological functions of sTrem2 in the murine ICH brain by stereotaxic injection of recombinant sTrem2 protein or by adeno-associated virus-mediated expression. Erythrocyte phagocytosis was assessed using flow cytometry and immunofluorescence. Western blotting was performed to evaluate protein expression. Changes in behavior, sTrem2-induced down-stream pathway, and microglia were examined. RESULTS: sTrem2 impedes hematoma resolution and impairs functional motor and sensory recovery. Interestingly, sTrem2 bypasses full-length Trem2, negatively regulating microglial/macrophage erythrophagocytosis, and promotes an inflammatory phenotype, which is associated with reduced retromer levels and impaired recycling of the pro-erythrophagocytic receptor CD36. Rescue of retromer Vps35 abolishes the phagocytosis-inhibiting effects and lysosome-dependent CD36 degradation caused by sTrem2. CONCLUSION: These findings indicate sTrem2 as a negative factor against microglia/macrophage-mediated hematoma and related neuronal damage clearance, provide insight into the mechanisms by which erythrophagocytosis is regulated and how it may be impaired after ICH, and suggest that the anti-proteolytic activity of Trem2 can be explored for ICH therapy.

Clinical and genetic characterization of Epstein-Barr virus-associated T/NK-cell lymphoproliferative diseases.

BACKGROUND: Epstein-Barr virus (EBV)-associated T-/natural killer (T/NK)-cell lymphoproliferative diseases clinically take on various forms, ranging from an indolent course to an aggressive condition. OBJECTIVE: Clinically, failure to establish precise diagnosis and provide proper treatment makes it difficult to help patients. We sought to better understand the underlying pathogenesis and to identify genetic prognostic factors to achieve better treatment efficacy. METHODS: In this study, 119 cases of EBV-associated lymphoproliferative diseases, including EBV-associated hemophagocytic lymphohistiocytosis (n = 46) and chronic active EBV disease of T/NK cell type (n = 73), were retrospectively examined. RESULTS: Adults aged >20 years at onset accounted for 71.4% of our cohort. About 54.6% patients with unfavorable overall survival developed hemophagocytic lymphohistiocytosis and had higher plasma EBV load. Allogenic hematopoietic stem-cell transplantation was the sole independent favorable factor. We systematically screened germline and somatic aberrations by whole-exome and targeted sequencing. Among 372 antiviral immunity genes, germline variants of 8 genes were significantly enriched. From a panel of 24 driver genes, somatic mutations were frequently identified in dominant EBV-infected T/NK cells. Patients carrying any germline/somatic aberrations in epigenetic modifiers and RIG-I-like receptor (RLR) pathway had worse overall survival than those without 2 type aberrations. Importantly, patients with IFIH1 and/or DDX3X aberrations in the RLR pathway had higher plasma and NK-cell EBV load. Knockdown of DDX3X in NKYS cells downregulated RLR signaling activities and elevated the expression of EBV-encoded oncogenes such as LMP1 and EBNA1. CONCLUSION: Genetic defects were prevalent in adult EBV-associated hemophagocytic lymphohistiocytosis patients and patients with chronic active EBV disease of T/NK cell type; these defects were associated with unfavorable prognosis. These findings can help clinicians work out more precise staging of the condition and provide new insights into these EBV-associated diseases.

Haemophagocytic lymphohistiocytosis and Epstein-Barr virus: a complex relationship with diverse origins, expression and outcomes.

Epstein-Barr virus (EBV) is a ubiquitous herpesvirus with rare but severe potential for lymphoproliferative complications. EBV is associated with a variety of presentations of haemophagocytic lymphohistiocytosis (HLH). HLH is a life-threatening hyperinflammatory syndrome that can occur in patients with genetic defects associated with dysregulation of the immune response (familial HLH) or arise in patients with underlying infection or malignancy (non-familial or secondary HLH). EBV can both serve as the incidental trigger of familial HLH or as the driving factor in patients with selective inherited vulnerability (e.g. X-linked lymphoproliferative disease). Alternatively, acute infection can idiosyncratically cause non-neoplastic HLH in patients without inherited predisposition (i.e. secondary HLH), while EBV-associated T/natural killer (NK)-cell lymphoproliferative disorders and lymphomas can cause neoplasia-associated HLH. The present review will discern between EBV-associated familial and non-familial HLH and highlight diagnostic and therapeutic considerations. Non-familial EBV-associated HLH is a major diagnostic dilemma, as it represents a diverse spectrum of disease ranging from highly curable (non-neoplastic EBV-HLH) to indolent but incurable (chronic active EBV) to acutely fatal (systemic EBV-positive T-cell lymphoma of childhood). Increased clinical awareness and understanding of this rare and potentially devastating subset of EBV-related complications is desperately needed to improve survival for patients with neoplasia-associated HLH.

Digenic Inheritance: Evidence and Gaps in Hemophagocytic Lymphohistiocytosis.

Hemophagocytic lymphohistiocytosis (HLH) is a hyperinflammatory disorder characterized by the inability to properly terminate an immune response. Familial HLH (FHLH) and related immune dysregulation syndromes are associated with mutations in the genes PRF1, UNC13D, STX11, STXBP2, LYST, AP3B1, and RAB27A, all of which are required for the assembly, exocytosis, and function of cytotoxic granules within CD8+ T cells and natural killer (NK) cells. Loss-of-function mutations in these genes render the cytotoxicity pathway ineffective, thereby failing to eradicate immune stimuli, such as infectious pathogens or malignant cells. The resulting persistent immune system stimulation drives hypercytokinemia, ultimately leading to severe tissue inflammation and end-organ damage. Traditionally, a diagnosis of FHLH requires the identification of biallelic loss-of-function mutations in one of these degranulation pathway genes. However, this narrow definition fails to encompass patients with other genetic mechanisms underlying degranulation pathway dysfunction. In particular, mounting clinical evidence supports a potential digenic mode of inheritance of FHLH in which single loss-of-function mutations in two different degranulation pathway genes cooperate to impair pathway activity. Here, we review the functions of the FHLH-associated genes within the degranulation pathway and summarize clinical evidence supporting a model in which cumulative defects along this mechanistic pathway may underlie HLH.

A hungry Histiocyte, altered immunity and myriad of problems: Diagnostic challenges for Pediatric HLH.

INTRODUCTION: Hemophagocytic lymphohistiocytosis (HLH) is an immune deregulation disorder with varied clinical presentation which clinically overlaps with widespread tropical infections. METHODS: We conducted a retrospective chart review of children diagnosed with HLH at our center from February-2017 to October-2020. RESULTS: Out of the nine diagnosed patients, genetic predisposition was present in three children; two had identified infectious triggers. The mean age of presentation was 30 months with male predominance. The most common clinical findings were fever, organomegaly, and pancytopenia. The median value of fibrinogen was-156 mg/dL, ferritin-12 957 ng/mL and for triglycerides-349 mg/dL, respectively. In children with identified genetic predisposition, serum ferritin levels were usually more than 10 000 ng/mL. The majority of our patients had evidence of hemophagocytosis on bone marrow examination. In our experience, although nonspecific, very high ferritin and serum triglycerides with low fibrinogen in a patient with bi-cytopenia, pancytopenia was the most suggestive evidence of HLH. Genetic evaluation in our series identified three children, one with primary HLH genetic mutation and two with underlying immune deficiency syndrome. The presence of HLH in the accelerated phase of Chediak-Higashi and AD Hyper IgE syndrome with HLH is extremely rare. Leishmaniasis (in nonendemic area) and Ebstein-Barr virus (EBV) was identified as an infectious trigger in two cases. Most of our cases received treatment as per HLH 2004 protocol. Three children died during the initial diagnosis and treatment. HLH with subcutaneous panniculitis-like T-cell lymphoma recovered well. CONCLUSION: HLH remains a life-threatening disorder associated with a variety of underlying illnesses as highlighted by our case series.

Central nervous system involvement in adult-onset relapsing hemophagocytic lymphohistiocytosis responsive to maintenance treatment with anakinra.

A 43 year-old male presented with a relapsing and progressive systemic inflammatory disorder with central nervous system (CNS) involvement. After a two years follow up, he was diagnosed with hemophagocytic lymphohistiocytosis (HLH), based on clinical, laboratory and radiological findings. Treatment was started with anakinra, a recombinant humanised interleukin-1 (IL-1) receptor antagonist. Clinical response was good. Laboratory and radiological findings showed no disease activity throughout a five years follow-up period. Several immunosuppressive agents have been used in HLH without any good outcomes. This is the first case report of HLH with CNS involvement responsive to chronic treatment with anakinra.

Monocytes From Patients With Macrophage Activation Syndrome and Secondary Hemophagocytic Lymphohistiocytosis Are Hyperresponsive to Interferon Gamma.

Objective: To investigate the activation of the IFNγ signaling pathway in monocytes of patients with secondary hemophagocytic lymphohistiocytosis (sHLH)/macrophage activation syndrome (MAS) and to evaluate whether levels of phosphorylated STAT1 represent a biomarker for the identification of patients at early stages of the disease. Methods: Fresh whole blood samples from pediatric patients with active sHLH/MAS, not receiving (n=10) and receiving glucocorticoids (n=14) at time of sampling, were prospectively collected. As disease control groups, patients with active systemic juvenile idiopathic arthritis (sJIA) without MAS, patients with sHLH/MAS in remission and patients with other rheumatic diseases were also sampled. Whole blood cells were left unstimulated or stimulated with increasing concentrations of IFNγ for 10 minutes and the intracellular Tyrosine (701)-phosphorylated STAT1 (pSTAT1) levels were evaluated in monocytes by flow cytometry. Results: Monocytes from untreated sHLH/MAS patients showed significantly higher basal levels of pSTAT1 compared to those observed in monocytes from glucocorticoid-treated sHLH/MAS patients and from all the other disease controls. In addition, a significant increase in responsiveness to IFNγ, as assessed by increased levels of pSTAT1 following ex vivo stimulation, was observed in monocytes from untreated sHLH/MAS patients. pSTAT1 levels in monocytes distinguished patients with sHLH/MAS not treated with glucocorticoids from patients with active sJIA or with other rheumatic diseases [AUC, 0.93; 95% confidence interval 0.85-1.00, p<0.001]. Statistically significant correlations between IFNG mRNA levels in whole blood cells, circulating IFNγ levels and pSTAT1 levels in sHLH/MAS monocytes were found. Conclusion: Our data demonstrating higher basal levels of pSTAT1 as well as a hyperreactivity to IFNγ stimulation in monocytes from patients with sHLH/MAS point to perturbations in the activation of downstream IFNγ signaling pathway as a contributor to the hyperinflammation occurring in these patients. Finally, the observation that glucocorticoids affect pSTAT1 levels in vivo, makes it difficult to consider the measurement of pSTAT1 levels as a biomarker to identify patients at early stages of sHLH/MAS in clinical practice.

The Spectrum of Clinical, Immunological, and Molecular Findings in Familial Hemophagocytic Lymphohistiocytosis: Experience From India.

Hemophagocytic lymphohistiocytosis (HLH) is a syndrome of immune dysregulation characterized by hyperactivation of the immune system, excessive cytokine secretion and severe systemic inflammation. HLH is classified as familial (FHL) when associated with mutations in PRF1, UNC13D, STX11, and STXBP2 genes. There is limited information available about the clinical and mutational spectrum of FHL patients in Indian population. This study is a retrospective analysis of 101 molecularly characterized FHL patients over the last 10 years from 20 different referral centers in India. FHL2 and FHL3 together accounted for 84% of cases of FHL in our cohort. Patients belonging to different FHL subtypes were indistinguishable based on clinical and biochemical parameters. However, flow cytometry-based assays viz. perforin expression and degranulation assay were found to be specific and sensitive in diagnosis and classification of FHL patients. Molecular characterization of respective genes revealed 76 different disease-causing mutations including 39 (51%) novel mutations in PRF1, UNC13D, STX11, and STXBP2 genes. Overall, survival was poor (28%) irrespective of the age of onset or the type of mutation in our cohort. Altogether, this article sheds light on the current scenario of FHL in India. Our data reveal a wide genetic heterogeneity of FHL in the Indian population and confirms the poor prognosis of FHL. This study also emphasizes that though mutational analysis is important for diagnostic confirmation of FHL, flow cytometry based assays help significantly in rapid diagnosis and functional validation of novel variants identified.

Diagnostic strategy for trigger identification in severe reactive hemophagocytic lymphohistiocytosis: A diagnostic accuracy study.

Reactive hemophagocytic lymphohistiocytosis (rHLH) management requires early recognition, trigger identification, and adequate treatment in order to reduce mortality. We assessed the diagnostic yield of tissue biopsies to identify trigger in severe rHLH. We included all consecutive patients presenting an rHLH diagnosis (HLH-2004 criteria) admitted to the intensive care unit (ICU) of a tertiary hospital. This retrospective diagnostic accuracy study was conducted according to the Standards for Reporting Diagnostic Accuracy Statement. Among the 134 included patients (median age 47 years [IQR 47-56]), an underlying immunodeficiency was previously known in 61.2%. rHLH trigger was identified in 127 patients (94.8%) (hematological disorder 75%, infection 16%, systemic disease 4%). Diagnostic yield of tissue biopsies was as follows: lymph node 75% (95% confidence interval [CI], 61-85), skin 50% (95% CI, 27-73), bone marrow 44% (95% CI, 34-55), liver 30% (95% CI, 15-49). Splenectomy (yield 77%; 95% CI, 46-95) was reserved to cases of diagnostic deadlock. Procedural severe adverse events included two cases of reversible hemorrhagic shock. Seventy-eight percent of patients received etoposide regarding to the rHLH severity, and 68% could receive trigger-specific treatment in the ICU. A comprehensive diagnostic workup led to an rHLH trigger identification in 95% of patients, allowing prompt initiation of appropriate therapy. Prospective studies to validate a standardized diagnostic approach are warranted.

Haemophagocytic lymphohistiocytosis that spontaneously resolved: a case of EBV.

A 23-year-old Caucasian woman, presented with recurrent fevers, elevated liver function tests and pancytopenia. Her labs at presentation were white blood cells 1.5 ×109/L, haemoglobin 8 g/L, platelets 59 k/mcl, lactate dehydrogenase (LDH) over 2000 U/L, aspartate aminotransferase 593 U/L, alanine aminotransferase 1321 U/L, alkaline phosphatase 223 U/L and ferritin 7665 µg/L. Epstein-Barr virus (EBV) IgM and IgG antibodies were positive in serum. A soluble interleukin 2 receptor was elevated at 2458. A bone marrow biopsy revealed scattered macrophages containing erythrocytes and other cellular elements. Immunohistochemistry for CD68 highlighted macrophages with erythrophagocytosis and in situ hybridisation was positive for EBV. She met the diagnostic criteria for haemophagocytic lymphohistiocytosis (HLH). She was initially treated with broad spectrum antibiotics which were eventually discontinued once the diagnosis was established. Over a period of 2-3 weeks her fever, transaminitis, ferritin and LDH improved spontaneously. She continued to improve clinically and was subsequently discharged. HLH is an aggressive, life-threatening hyper-inflammatory syndrome which, if not promptly recognised and treated, can be fatal. Treatment involves etoposide-based chemotherapy and possible stem-cell transplantation. This patient showed signs of improvement spontaneously and a decision was made to not treat her. This was a rare case of EBV-associated HLH which resolved spontaneously without any intervention. This young patient was not subjected to unnecessary chemotherapy. So far only few cases of spontaneous resolution of EBV-associated HLH have been reported.

Contribution of clonal hematopoiesis to adult-onset hemophagocytic lymphohistiocytosis.

Adult-onset hemophagocytic lymphohistiocytosis (HLH) is a rare, life-threatening disease of immune hyperactivation. Unlike pediatric HLH, adult HLH is rarely driven by germline genetic variants. Although numerous precipitating etiologies have been identified, the reason that HLH occurs in only a subset of individuals and how other factors contribute to the disease remains unknown. We hypothesized that clonal hematopoiesis (CH), a state in which somatic mutations in blood cells cause an expanded population of mutant hematopoietic cells and drive an aberrant inflammatory state, could contribute to adult-onset HLH. In a highly annotated cohort of older adults with HLH we found that CH was more prevalent than in control cohorts. Using the adult-onset HLH mouse model in which repeated treatments of the TLR9 agonist, ODN1826, was delivered to the mouse, we observed that macrophages carrying mutations in Tet2, one of the most commonly mutated genes in CH, have an enhanced inflammatory response to TLR9 agonism. Finally, mice carrying Tet2 mutations in the hematopoietic compartment (a common model for CH) displayed an exaggerated response to TLR9 agonism, including worse splenomegaly and anemia. Our data suggest that CH is more common in individuals with adult-onset HLH and can contribute to the pathophysiology of this disease.

Falciparum malaria-induced secondary hemophagocytic lymphohistiocytosis successfully treated with ruxolitinib.

JAK/STAT signaling plays a major role in the pathogenesis of secondary hemophagocytic lymphohistiocytosis. This case report on a critically ill patient with secondary hemophagocytic lymphohistiocytosis due to falciparum malaria treated successfully with ruxolitinib, demonstrates that JAK1/2 inhibition might be a promising treatment option for severe cases.

Neuroinflammatory Disease as an Isolated Manifestation of Hemophagocytic Lymphohistiocytosis.

Isolated neuroinflammatory disease has been described in case reports of familial hemophagocytic lymphohistiocytosis (FHL), but the clinical spectrum of disease manifestations, response to therapy and prognosis remain poorly defined. We combined an international survey with a literature search to identify FHL patients with (i) initial presentation with isolated neurological symptoms; (ii) absence of cytopenia and splenomegaly at presentation; and (iii) systemic HLH features no earlier than 3 months after neurological presentation. Thirty-eight (20 unreported) patients were identified with initial diagnoses including acute demyelinating encephalopathy, leukoencephalopathy, CNS vasculitis, multiple sclerosis, and encephalitis. Median age at presentation was 6.5 years, most commonly with ataxia/gait disturbance (75%) and seizures (53%). Diffuse multifocal white matter changes (79%) and cerebellar involvement (61%) were common MRI findings. CSF cell count and protein were increased in 22/29 and 15/29 patients, respectively. Fourteen patients progressed to systemic inflammatory disease fulfilling HLH-2004 criteria at a mean of 36.9 months after initial neurological presentation. Mutations were detected in PRF1 in 23 patients (61%), RAB27A in 10 (26%), UNC13D in 3 (8%), LYST in 1 (3%), and STXBP2 in 1 (3%) with a mean interval to diagnosis of 28.3 months. Among 19 patients who underwent HSCT, 11 neurologically improved, 4 were stable, one relapsed, and 3 died. Among 14 non-transplanted patients, only 3 improved or had stable disease, one relapsed, and 10 died. Isolated CNS-HLH is a rare and often overlooked cause of inflammatory brain disease. HLH-directed therapy followed by HSCT seems to improve survival and outcome.