Nadine Voelxen

Circulating CD21low B cells in common variable immunodeficiency resemble tissue homing, innate-like B cells.

The homeostasis of circulating B cell subsets in the peripheral blood of healthy adults is well regulated, but in disease it can be severely disturbed. Thus, a subgroup of patients with common variable immunodeficiency (CVID) presents with an extraordinary expansion of an unusual B cell population characterized by the low expression of CD21. CD21low B cells are polyclonal, unmutated IgM+IgD+ B cells but carry a highly distinct gene expression profile which differs from conventional naïve B cells. Interestingly, while clearly not representing a memory population, they do share several features with the recently defined memory-like tissue, Fc receptor-like 4 positive B cell population in the tonsils of healthy donors. CD21low B cells show signs of previous activation and proliferation in vivo, while exhibiting defective calcium signaling and poor proliferation in response to B cell receptor stimulation. CD21low B cells express decreased amounts of homeostatic but increased levels of inflammatory chemokine receptors. This might explain their preferential homing to peripheral tissues like the bronchoalveolar space of CVID or the synovium of rheumatoid arthritis patients. Therefore, as a result of the close resemblance to the gene expression profile, phenotype, function and preferential tissue homing of murine B1 B cells, we suggest that CD21low B cells represent a human innate-like B cell population.

B Cell Receptor-Mediated Calcium Signaling Is Impaired in B Lymphocytes of Type Ia Patients with Common Variable Immunodeficiency

Several lines of evidence have demonstrated B cell intrinsic activation defects in patients with common variable immunodeficiency (CVID). The rapid increase of intracellular free calcium concentrations after engagement of the BCR represents one crucial element in this activation process. The analysis of 53 patients with CVID for BCR-induced calcium flux identified a subgroup of patients with significantly reduced Ca2+ signals in primary B cells. This subgroup strongly corresponded to the class Ia of the Freiburg classification. Comparison at the level of defined B cell subpopulations revealed reduced Ca2+ signals in all mature B cell populations of patients with CVID class Ia when compared with healthy individuals and other groups of patients with CVID but not in circulating transitional B cells. BCR-induced Ca2+ responses were the lowest in CD21low B cells in patients as well as healthy donors, indicating an additional cell-specific mechanism inhibiting the Ca2+ flux. Although proximal BCR signaling events are unperturbed in patients’ B cells, including normal phospholipase Cγ2 phosphorylation and Ca2+ release from intracellular stores, Ca2+ influx from the extracellular space is significantly impaired. CD22, a negative regulator of calcium signals in B cells, is highly expressed on CD21low B cells from patients with CVID Ia and might be involved in the attenuated Ca2+ response of this B cell subpopulation. These data from patients with CVID suggest that a defect leading to impaired BCR-induced calcium signaling is associated with the expansion of CD21low B cells, hypogammaglobulinemia, autoimmune dysregulation, and lymphadenopathy.

Comparative metabolic analysis in head and neck cancer and the normal gingiva

ObjectivesChronic accumulation of lactate in malignant tumor tissue is associated with increased malignancy and radioresistance. For this study, biopsies of primary head and neck squamous cell carcinoma (HNSCC) and of the normal gingiva of the same patient were compared via metabolic profiling to the healthy gingiva from cancer-free patients.Materials and methodsCryobiopsies of 140 HNSCC patients were used to determine ATP, lactate, and glucose concentrations of the tumor and normal gingiva via induced metabolic bioluminescence imaging (imBI). Additionally, these metabolites were quantified in a collective of 79 healthy (non-tumor-bearing) patients. Furthermore, tumor samples were analyzed via immunofluorescence imaging and quantitative real-time PCR for the expression of lactate and glucose transporters.ResultsThere were significant differences in ATP concentrations detectable between the tumor, normal gingiva of tumor patients, and gingiva from healthy patients. Lactate concentrations were significantly increased in tumor tissue compared to the normal gingiva of tumor patients as well as the gingiva from healthy patients. Concerning glucose, there was a significant decrease in glucose concentrations detectable in the tumor biopsies compared to the normal gingiva of tumor patients. On the other hand, tumor samples from patients revealed significantly elevated relative expression levels of monocarboxylate transporters (MCT-1 and MCT-4), as well as glucose transporters (GLUT-1 and GLUT-3) compared to the corresponding normal gingiva of each patient.ConclusionsWe could demonstrate that the lactate concentration in HNSCC correlates with primary tumor (T) stage.Clinical relevanceThe aim of this study was to identify metabolic parameters to improve early cancer diagnosis, allow predictions on the degree of malignancy, and contribute to a personalized tumor therapy.

B-cell signaling in persistent polyclonal B lymphocytosis (PPBL).

Persistent polyclonal B lymphocytosis (PPBL) is a benign hematological disorder characterized by a selective expansion of circulating polyclonal marginal zone (MZ)‐like B cells. Previous reports demonstrated that cases of PPBL showed poor activation, proliferation and survival of B cells in vitro, yet the underlying defect remains unknown. Here we report for the first time an attenuated activation of the canonical NF‐κB (nuclear factor of kappa light polypeptide gene enhancer in B cells) and mitogen‐activated protein kinase/extracellular signal‐regulated kinase pathway after CD40 stimulation. This defect was selective, as alternative NF‐κB signaling after CD40 stimulation and both B‐cell receptor‐ and Toll‐like receptor 9‐mediated activation remained unaffected. Reduced canonical NF‐κB activation resulted in decreased IκBα and CD40 expression in resting cells. In PPBL patients, expression of Bcl‐xL in MZ‐like B cells did not increase upon activation, consistent with the high apoptosis rates of PPBL‐derived B cells that were observed in vitro. The B‐cell phenotype of mice with selective knockouts of early components of the CD40 signaling pathway resembles PPBL, but sequencing corresponding genes in sorted MZ‐like B cells of PPBL patients did not reveal relevant genetic alterations. Nevertheless, the frequently observed mutations in early signaling components of the NF‐κB pathway in MZ lymphomas underline the relevance of our findings for the pathogenesis of PPBL.

Chronic social stress-induced hyperglycemia in mice couples individual stress susceptibility to impaired spatial memory

Significance Stress-associated mental disorders and diabetes pose an enormous socio-economic burden. Glucose dysregulation occurs with both psychosocial and metabolic stress. While cognitive impairments are common in metabolic disorders such as diabetes and are accompanied by hyperglycemia, a causal role for glucose has not been established. We show that chronic social defeat (CSD) stress induces lasting peripheral and central hyperglycemia and impaired glucose metabolism in a subgroup of mice. Animals exhibiting hyperglycemia early post-CSD display spatial memory impairments that can be rescued by the antidiabetic empagliflozin. We demonstrate that individual stress vulnerability to glucose homeostasis can be identified early after insult and that stress-induced hyperglycemia directly impinges on cognitive integrity. Our findings further bridge the gap between stress-related pathologies and metabolic disorders. Stringent glucose demands render the brain susceptible to disturbances in the supply of this main source of energy, and chronic stress may constitute such a disruption. However, whether stress-associated cognitive impairments may arise from disturbed glucose regulation remains unclear. Here we show that chronic social defeat (CSD) stress in adult male mice induces hyperglycemia and directly affects spatial memory performance. Stressed mice developed hyperglycemia and impaired glucose metabolism peripherally as well as in the brain (demonstrated by PET and induced metabolic bioluminescence imaging), which was accompanied by hippocampus-related spatial memory impairments. Importantly, the cognitive and metabolic phenotype pertained to a subset of stressed mice and could be linked to early hyperglycemia 2 days post-CSD. Based on this criterion, ∼40% of the stressed mice had a high-glucose (glucose >150 mg/dL), stress-susceptible phenotype. The relevance of this biomarker emerges from the effects of the glucose-lowering sodium glucose cotransporter 2 inhibitor empagliflozin, because upon dietary treatment, mice identified as having high glucose demonstrated restored spatial memory and normalized glucose metabolism. Conversely, reducing glucose levels by empagliflozin in mice that did not display stress-induced hyperglycemia (resilient mice) impaired their default-intact spatial memory performance. We conclude that hyperglycemia developing early after chronic stress threatens long-term glucose homeostasis and causes spatial memory dysfunction. Our findings may explain the comorbidity between stress-related and metabolic disorders, such as depression and diabetes, and suggest that cognitive impairments in both types of disorders could originate from excessive cerebral glucose accumulation.

Quantitative imaging of D-2- hydroxyglutarate in selected histological Tissue areas by a novel Bioluminescence Technique

Patients with malignant gliomas have a poor prognosis with average survival of less than 1 year. Whereas in other tumor entities the characteristics of tumor metabolism are successfully used for therapeutic approaches, such developments are very rare in brain tumors, notably in gliomas. One metabolic feature characteristic of gliomas, in particular diffuse astrocytomas and oligodendroglial tumors, is the variable content of D-2-hydroxyglutarate (D2HG), a metabolite that was discovered first in this tumor entity. D2HG is generated in large amounts due to various “gain-of-function” mutations in the isocitrate dehydrogenases IDH1 and IDH2. Meanwhile, D2HG has been detected in several other tumor entities, including intrahepatic bile-duct cancer, chondrosarcoma, acute myeloid leukemia, and angioimmunoblastic T-cell lymphoma. D2HG is barely detectable in healthy tissue (<0.1 mM), but its concentration increases up to 35 mM in malignant tumor tissues. Consequently, the “oncometabolite” D2HG has gained increasing interest in the field of tumor metabolism. To facilitate its quantitative measurement without loss of spatial resolution at a microscopical level, we have developed a novel bioluminescence assay for determining D2HG in sections of snap-frozen tissue. The assay was verified independently by photometric tests and liquid chromatography/mass spectrometry. The novel technique allows the microscopically resolved determination of D2HG in a concentration range of 0–10 μmol/g tissue (wet weight). In combination with the already established bioluminescence imaging techniques for ATP, glucose, pyruvate, and lactate, the novel D2HG assay enables a comparative characterization of the metabolic profile of individual tumors in a further dimension.