Robert J. Fallon

CXCR-4 Desensitization Is Associated with Tissue Localization of Hemopoietic Progenitor Cells

The chemokine stroma-derived factor (SDF)-1, and its receptor, CXCR-4, have been shown to be essential for the translocation of hemopoietic stem cells from the fetal liver to the bone marrow (BM). We hypothesized that if CXCR-4 plays a crucial role in the localization of human hemopoiesis, stem cells from distinct tissue sources should demonstrate distinct CXCR-4 expression or signaling profiles. CD34+ cells from BM were compared with blood: either mobilized peripheral blood or umbilical cord blood. Unexpectedly, significantly higher levels of CXCR-4 surface expression on CD34+ cells from blood sources, mobilized peripheral blood, or cord blood were observed compared with BM (p = 0.0005 and p = 0.002, respectively). However, despite lower levels of CXCR-4, responsiveness of the cells to SDF-1 as measured by either calcium flux or transmigration was proportionally greatest in cells derived from BM. Further, internalization of CXCR-4 in response to ligand, associated with receptor desensitization, was significantly lower on BM-derived cells. Therefore, preserved chemokine receptor signaling was highly associated with marrow rather than blood localization. To test the functional effects of perturbing CXCR-4 signaling, adult mice were exposed to the methionine-SDF-1β analog that induces prolonged down-regulation/desensitization of CXCR-4 and observed mobilization of Lin−, Sca-1+, Thy-1low, and c-kit+ hemopoietic progenitor cells to the peripheral blood with a >30-fold increase compared with PBS control (p = 0.0007 day 1 and p = 0.004 day 2). These data demonstrate that CXCR-4 expression and function can be dissociated in progenitor cells and that desensitization of CXCR-4 induces stem cell entry into the circulation.

The serpin-enzyme complex (SEC) receptor mediates the neutrophil chemotactic effect of alpha-1 antitrypsin-elastase complexes and amyloid-beta peptide.

The serpin-enzyme complex (SEC) receptor mediates catabolism of alpha 1-antitrypsin (alpha 1-AT)-elastase complexes and increases in synthesis of alpha 1-AT in cell culture. The SEC receptor recognizes a pentapeptide domain on alpha 1-AT-elastase complexes (alpha 1-AT 370-374), and the same domain in several other serpins, amyloid-beta peptide, substance P, and other tachykinins. Thus, it has also been implicated in the biological properties of these ligands, including the neurotoxic effect of amyloid-beta peptide. In this study, we examined the possibility that the SEC receptor mediates the previously described neutrophil chemotactic activity of alpha 1-AT-elastase complexes, and whether the other ligands for the SEC receptor have neutrophil chemotactic activity. The results show that 125I-peptide 105Y (based on alpha 1-AT 359-374) binds specifically and saturably to human neutrophils, and the characteristics of this binding are almost identical to that of monocytes and hepatoma-derived hepatocytes. Peptide 105Y and amyloid-beta peptide mediate chemotaxis for neutrophils with maximal stimulation at 1-10 nM. Mutant or deleted forms of peptide 105Y, which do not bind to the SEC receptor, have no effect. The neutrophil chemotactic effect of alpha 1-AT-elastase complexes is blocked by antiserum to peptide 105Y and by antiserum to the SEC receptor, but not by control antiserum. Preincubation of neutrophils with peptide 105Y or substance P completely blocks the chemotactic activity of amyloid-beta peptide, but not that of FMLP. These results, therefore, indicate that the SEC receptor can be modulated by homologous desensitization and raise the possibility that pharmacological manipulation of this receptor will modify the local tissue response to inflammation/injury and the neuropathologic reaction of Alzheimers disease.

Risk-prediction tool for identifying hospitalized children with a predisposition for development of venous thromboembolism: Peds-Clot clinical Decision Rule

Summary.  Background:  The prevalence of VTE is increasing in tertiary pediatric hospitals. Identification of high‐risk populations using uniform criteria is required to develop evidence‐based VTE prevention guidelines.

Esthesioneuroblastoma in children

Esthesioneuroblastoma (olfactory neuroblastoma) is a rare tumor of the olfactory epithelium. Approximately 1,000 cases have been described in the literature since the original description in 1924. It occurs in older individuals and is rare in children. The authors describe the clinicopathologic presentation in a series of five children treated with neoadjuvant/adjuvant chemotherapy and review the English literature for previously described patients younger than 18 years to assess clinical presentation, mode of treatment, and outcome in this age group.

Clinical course of postthrombotic syndrome in children with history of venous thromboembolism.

Postthrombotic syndrome (PTS) is a chronic morbidity of venous thromboembolism (VTE) in children. Information about the evolution of PTS is lacking in children. Present study was aimed to evaluate the time-course of extremity PTS in children who were serially followed in a hematology clinic. This retrospective cohort study included 69 consecutive children with documented VTEs that presented with symptoms of extremity VTE: 67 extremity VTEs with or without extension to vena cava, 2 inferior vena cava VTEs. Severity of PTS was assessed using modified Villalta scale. Median age of the cohort was 12.6 years (interquartile range 1.6–15 years) while median follow-up was 28.7 months (interquartile range 13.3–33.4 months. PTS prevalence was 46.8% [95% confidence interval (CI) 37.9–57.7%]. Lower extremity VTE was associated with development of PTS compared to upper extremity VTE regardless of catheter use (P = 0.002). The time-course of PTS fluctuated in 11 of 33 children (33%; 95% CI 20–47%) at a median interval of 12 months from diagnosis of VTE (range 4–14 months): three progressed from mild/moderate to severe, one improved from moderate to mild, seven fluctuated between mild and moderate. Recurrence and incomplete resolution of VTE were associated with variability in PTS severity (P < 0.05). In summary, this study suggested that almost 50% of study cohort developed PTS, and the time-course of PTS was not static in one third of children. Future research should focus on identifying the predictors contributing to the worsening of PTS and developing risk-stratified treatment interventions so as to improve the outcome of children with VTE.

Deletion of 3'-CBFB gene in association with an inversion (16)(p13q22) and a loss of the Y chromosome in a 2-year-Old child with acute myelogenous leukemia-M4.

Inversion 16(p13q22) is most commonly associated with acute myelomonocytic leukemia with abnormal eosinophils (M4). In association with this inversion, a proximal deletion at the 16p13 primary arm breakpoint occurs in 20% of cases. We report on a first case of inversion 16 with a distal deletion at the primary arm breakpoint 16q22, detected by using the fluorescent-labeled dual-color probe CBFB.

Reduction in Overt and Silent Stroke Recurrence Rate Following Cerebral Revascularization Surgery in Children with Sickle Cell Disease and Severe Cerebral Vasculopathy

Children with sickle cell disease (SCD) and moyamoya may benefit from indirect cerebral revascularization surgery in addition to chronic blood transfusion therapy for infarct prevention. We sought to compare overt and silent infarct recurrence rates in children with SCD undergoing revascularization.