A silicon-based device, dubbed a microphysiometer, can be used to detect and monitor the response of cells to a variety of chemical substances, especially ligands for specific plasma membrane receptors. The microphysiometer measures the rate of proton excretion from 10(4) to 10(6) cells. This article gives an overview of experiments currently being carried out with this instrument with emphasis on receptors with seven transmembrane helices and tyrosine kinase receptors. As a scientific instrument, the microphysiometer can be thought of as serving two distinct functions. In terms of detecting specific molecules, selected biological cells in this instrument serve as detectors and amplifiers. The microphysiometer can also investigate cell function and biochemistry. A major application of this instrument may prove to be screening for new receptor ligands. In this respect, the microphysiometer appears to offer significant advantages over other techniques.

G-CSF stimulates mobilization of hematopoietic progenitor cells (HPCs) from bone marrow by disrupting the CXCR4/SDF-1alpha retention axis. We show here that distinct factors and mechanisms regulate the mobilization of endothelial (EPCs) and stromal progenitor cells (SPCs). Pretreatment of mice with VEGF did not disrupt the CXCR4/SDF-1alpha chemokine axis but stimulated entry of HPCs into the cell cycle via VEGFR1, reducing their migratory capacity in vitro and suppressing their mobilization in vivo. In contrast, VEGF pretreatment enhanced EPC mobilization via VEGFR2 in response to CXCR4 antagonism. Furthermore, SPC mobilization was detected when the CXCR4 antagonist was administered to mice pretreated with VEGF, but not G-CSF. Thus, differential mobilization of progenitor cell subsets is dependent upon the cytokine milieu that regulates cell retention and proliferation. These findings may inform studies investigating mechanisms that regulate progenitor cell recruitment in disease and can be exploited to provide efficacious stem cell therapy for tissue regeneration.

In this study, we have identified a unique combinatorial effect of the chemokines KC/MIP-2 and the cytokine granulocyte colony-stimulating factor (G-CSF) with respect to the rapid mobilization of neutrophils from the bone marrow in a model of acute peritonitis. At 2 hours following an intraperitoneal injection of thioglycollate, there was a 4.5-fold increase in blood neutrophil numbers, which was inhibited 84% and 72% by prior administration of blocking mAbs against either the chemokines KC/MIP-2 or G-CSF, respectively. An intraperitoneal injection of G-CSF acted remotely to stimulate neutrophil mobilization, but did not elicit recruitment into the peritoneum. Further, in vitro G-CSF was neither chemotactic nor chemokinetic for murine neutrophils, and had no priming effect on chemotaxis stimulated by chemokines. Here, we show that, in vitro and in vivo, G-CSF induces neutrophil mobilization by disrupting their SDF-1α–mediated retention in the bone marrow. Using an in situ perfusion system of the mouse femoral bone marrow to directly assess mobilization, KC and G-CSF mobilized 6.8 × 106 and 5.4 × 106 neutrophils, respectively, while the infusion of KC and G-CSF together mobilized 19.5 × 106 neutrophils, indicating that these factors act cooperatively with respect to neutrophil mobilization.

No abstract

Platelets are necessary for lung leukocyte recruitment in a murine model of allergic inflammation, and platelet-leukocyte aggregates are formed in circulating blood of patients with asthma after allergen exposure. However, it is unknown how platelets induce pulmonary leukocyte recruitment in asthma. Here, we have investigated the importance of platelet adhesion molecule expression on pulmonary eosinophil and lymphocyte recruitment and on leukocyte CD11b and very late antigen (VLA)-4 expression in mice. Pulmonary leukocyte recruitment in platelet-depleted mice (sensitized and exposed to ovalbumin) transfused with fixed, unstimulated platelets (FUSPs) was abolished, whereas transfusion with platelets stimulated and fixed (FSPs), expressing P-selectin and P-selectin glycoprotein ligand-1 (PSGL-1), restored eosinophil and lymphocyte recruitment. Transfusion with platelets from P-selectin-deficient mice, or with FSPs stimulated in the presence of a blocking anti-P-selectin antibody, were unable to restore pulmonary leukocyte recruitment. Flow cytometric analysis revealed increased expression of CD11b and VLA-4 on leukocytes attached to platelets after allergen exposure, and CD11b expression on leukocytes was suppressed in thrombocytopenic mice but was restored with the transfusion of FSPs, but not FUSPs, a phenomenon concurrent with the formation of platelet-leukocyte complexes. Pselectin expression on the surfaces of platelets is a major requirement for pulmonary eosinophil and lymphocyte recruitment, allowing circulating platelets to bind to and stimulate leukocytes for endothelial attachment.