Stefanie Bugl

Steady-state neutrophil homeostasis is dependent on TLR4/TRIF signaling

UNLABELLED Polymorphonuclear neutrophil granulocytes (neutrophils) are tightly controlled by an incompletely understood homeostatic feedback loop adjusting the marrows supply to peripheral needs. Although it has long been known that marrow cellularity is inversely correlated with G-CSF levels, the mechanism linking peripheral clearance to production remains unknown. Herein, the feedback response to antibody induced neutropenia is characterized to consist of G-CSF–dependent shifts of marrow hematopoietic progenitor populations including expansion of the lin-/Sca-1/c-kit (LSK) and granulocyte macrophage progenitor (GMP) compartments at the expense of thrombopoietic and red cell precursors. Evidence is provided that positive feedback regulation is independent from commensal germs as well as T, B, and NK cells. However, in vivo feedback is impaired in TLR4-/- and TRIF-/-, but not MyD88-/- animals. In conclusion, steady-state neutrophil homeostasis is G-CSF–dependent and regulated through pattern-recognition receptors,thereby directly linking TLR-triggering to granulopoiesis. KEY POINTS Steady-state and emergency granulopoiesis are both dependent on TLR signaling.

Differential changes in platelet VEGF, Tsp, CXCL12, and CXCL4 in patients with metastatic cancer

Data from animal studies indicate that platelets play a key role in tumor dissemination and metastasis. We therefore hypothesized that metastastic cancer patients may display a specific platelet phenotype. Percentage of activated, p-selectin positive platelets as well as platelet contents (i.e., plasma and platelet count-corrected serum levels of VEGF-A, CXCL12, CXCL4, and thrombospondin-1) were analyzed in 43 patients with newly diagnosed metastatic disease prior to treatment. Tumor patients had increased platelet counts and significantly elevated percentages of activated platelets. Moreover, the platelet content of VEGF-A in cancer patients was significantly increased compared to healthy controls, while thrombospondin-1, CXCL12 and CXCL4 were significantly decreased. Our data contain several unexpected results: firstly, CXCL12 was found in minute quantities in the serum as compared with murine studies. Secondly, CXCL4, which was found by mass spectrometry to be the single massively upregulated intraplatelet chemokine in mice after tumor xenotransplantation, was decreased in tumor patient platelets. While increased contents of VEGF-A have been attributed to platelet scavenger activity, the differential decrease of specific platelet contents may be due to differential secretion or altered megakaryopoiesis in metastatic cancer patients.

Current insights into neutrophil homeostasis

Neutrophil granulocytes represent the first immunologic barrier against invading pathogens, and neutropenia predisposes to infection. However, neutrophils may also cause significant collateral inflammatory damage. Therefore, neutrophil numbers are tightly regulated by an incompletely understood homeostatic feedback loop adjusting the marrows supply to peripheral needs. Granulocyte colony‐stimulating factor (G‐CSF) is accepted to be the major determinant of neutrophil production, and G‐CSF levels have, soon after its discovery, been described to be inversely correlated with neutrophil counts. A neutrophil sensor, or “neutrostat,” has, therefore, been postulated. The prevailing feedback hypothesis was established in adhesion molecule–deficient mice; it includes macrophages and Th17 cells, which determine G‐CSF levels in response to the number of peripherally transmigrated, apoptosing neutrophils. Recent work has deepened our understanding of homeostatic regulation of neutrophil granulopoiesis, but there are still inconsistent findings and unresolved questions when it comes to a plausible hypothesis, similar to the feedback control models of red cell or platelet homeostasis.

Neutrophil homeostasis and its regulation by danger signaling

Hematopoiesis in general is demand driven and adaptive, but in contrast to erythropoiesis or thrombocytopoiesis, our knowledge on how neutrophil production is adapted to individual needs remains incomplete. Recently, neutrophil homeostasis has been shown to depend on danger receptors, macrophages, and even circadian rhythms. Puzzle pieces for a broader view of neutrophil homeostasis accumulate, and we will herein try to put seemingly contradictory evidence in a perspective of neutrophil homeostasis and emergency granulopoiesis determined by innate immunologic signaling.

NFAT2 is a critical regulator of the anergic phenotype in chronic lymphocytic leukaemia.

Chronic lymphocytic leukaemia (CLL) is a clonal disorder of mature B cells. Most patients are characterised by an indolent disease course and an anergic phenotype of their leukaemia cells, which refers to a state of unresponsiveness to B cell receptor stimulation. Up to 10% of CLL patients transform from an indolent subtype to an aggressive form of B cell lymphoma over time (Richter´s syndrome) and show a significantly worse treatment outcome. Here we show that B cell-specific ablation of Nfat2 leads to the loss of the anergic phenotype culminating in a significantly compromised life expectancy and transformation to aggressive disease. We further define a gene expression signature of anergic CLL cells consisting of several NFAT2-dependent genes including Cbl-b, Grail, Egr2 and Lck. In summary, this study identifies NFAT2 as a crucial regulator of the anergic phenotype in CLL.NFAT2 is a transcription factor that has been linked with chronic lymphocytic leukaemia (CLL), but its functions in CLL manifestation are still unclear. Here the authors show, by analysing mouse CLL models and characterising biopsies from CLL patients, that NFAT2 is an important regulator for the anergic phenotype of CLL.

Paraneoplastic granulocyte colony-stimulating factor secretion in soft tissue sarcoma mimicking myeloproliferative neoplasia: a case report

BackgroundWhile paraneoplastic leukocytosis is a common phenomenon in solid tumors, extreme elevations of white blood counts (WBC) in the range of more than 100,000/μl are uncommon in patients with non-hematologic malignancies. Leukocytosis with mature neutrophils due to a granulocyte colony-stimulating factor (G-CSF) producing tumor is only seen on rare occasions.Case presentationMassive neutrophil leukocytosis of approximately 100,000/μl was diagnosed in a 57-year-old Caucasian woman with metastatic undifferentiated endometrial sarcoma. A bone marrow trephine biopsy revealed massively increased granulopoiesis, but no evidence of monoclonal myeloproliferative disease. After the primary tumor had been resected, white blood count (WBC) plummeted and went back to nearly normal levels within one week. With progressive metastatic disease, granulocyte colony-stimulating factor (G-CSF) plasma levels were found to be increased by 10-fold. White blood count (WBC) strictly correlated with tumor burden and response to chemotherapy. In the final stage of treatment resistent disease, white blood count (WBC) approximated 300,000/μl.ConclusionWe report on a granulocyte colony-stimulating factor (G-CSF) secreting undifferentiated endometrial sarcoma, which was associated with extreme neutrophil counts. White blood count (WBC) were closely correlated with tumor burden and associated with an aggressive clinical course. We suggest that paraneoplastic neutrophilia represents a poor prognostic sign in soft tissue sarcoma. In patients with similar constellations, antitumor therapy must not be delayed.