Lectin and epidermal growth factor domains of P-selectin at physiologic density are the recognition unit for leukocyte binding

P-selectin is an integral membrane glycoprotein on stimulated platelets and endothelial cells that serves as a receptor for leukocytes. To estimate the density of P-selectin in membranes necessary to support adhesion, we incorporated purified P-selectin at varying concentrations into phospholipid bilayers that encapsulated glass microspheres. Maximal binding of these lipospheres to HL60 cells, a P-selectin ligand- expressing cell line, was approached at a P-selectin density of about 100 molecules per microns 2; half-maximal binding was observed at about 50 to 60 molecules per microns 2. Compatible results were obtained with P-selectin expressed on Chinese hamster ovary cells. The P-selectin density on stimulated platelets was estimated to be 150 to 200 molecules/microns 2. To identify the domains of P-selectin required for HL60 cell binding, chimeras of P-selectin and L-selectin were stably expressed in Chinese hamster ovary cells and clones that expressed the chimeras at the estimated physiologic density were selected. Chimeras containing the P-selectin lectin and epidermal growth factor (EGF) domains or the lectin, EGF, and short consensus repeats bound HL60 cells equivalently, but a chimera containing the P-selectin lectin domain alone bound HL60 cells much less well. These results indicate that at a physiologically relevant P-selectin density on membrane surfaces, the lectin, and EGF domains of P-selectin are together required for optimal leukocyte binding.     

Experience with a transfusion recipient education program about hepatitis C

Shortly after test kits for antibodies to the hepatitis C virus (HCV) were licensed in May of 1990, our medical community undertook a public education program encouraging previous transfusion recipients to see their physicians about the wisdom of being tested for anti-HCV. In response, 1034 samples were received for testing. All samples repeatably reactive (RR) with anti-HCV enzyme-linked immunoassay (EIA) were tested further with a research recombinant immunoblot assay (RIBA). Overall, 76 of the 1034 (7.4%) recipient samples were RR and 64 of these (84.2%) were reactive with RIBA. Recipients transfused prior to surrogate testing (alanine aminotransferase [ALT] and anti-hepatitis B core [anti-HBc]) in 1986 showed a 8.6 percent reactivity with RIBA and those transfused after surrogate testing showed a 4.8 percent reactivity, a 44 percent reduction. Of the 57 recipient samples reactive with RIBA and suitable for assay, 11 (19.3%) had an elevated ALT. Among 76 randomly selected blood donors with RR EIAs studied for comparison with recipients, 20 (26.3%) were reactive with RIBA, 9 of which had an abnormal surrogate test that would have disqualified them. ALT concentrations were abnormal in 6 (30%) of the donors who were reactive on RIBA. We conclude that an education program that encourages previous transfusion recipients to seek medical advice about anti-HCV testing is practical from the standpoint of the blood center. We believe more widespread implementation of similar programs should be considered.(ABSTRACT TRUNCATED AT 250 WORDS)     

Presynaptically located CB1 cannabinoid receptors regulate GABA release from axon terminals of specific hippocampal interneurons

To understand the functional significance and mechanisms of action in the CNS of endogenous and exogenous cannabinoids, it is crucial to identify the neural elements that serve as the structural substrate of these actions. We used a recently developed antibody against the CB1 cannabinoid receptor to study this question in hippocampal networks. Interneurons with features typical of basket cells showed a selective, intense staining for CB1 in all hippocampal subfields and layers. Most of them (85.6%) contained cholecystokinin (CCK), which corresponded to 96.9% of all CCK-positive interneurons, whereas only 4.6% of the parvalbumin (PV)-containing basket cells expressed CB1. Accordingly, electron microscopy revealed that CB1-immunoreactive axon terminals of CCK-containing basket cells surrounded the somata and proximal dendrites of pyramidal neurons, whereas PV-positive basket cell terminals in similar locations were negative for CB1. The synthetic cannabinoid agonist WIN 55,212-2 (0.01-3 microM) reduced dose-dependently the electrical field stimulation-induced [3H]GABA release from superfused hippocampal slices, with an EC50 value of 0. 041 microM. Inhibition of GABA release by WIN 55,212-2 was not mediated by inhibition of glutamatergic transmission because the WIN 55,212-2 effect was not reduced by the glutamate blockers AP5 and CNQX. In contrast, the CB1 cannabinoid receptor antagonist SR 141716A (1 microM) prevented this effect, whereas by itself it did not change the outflow of [3H]GABA. These results suggest that cannabinoid-mediated modulation of hippocampal interneuron networks operate largely via presynaptic receptors on CCK-immunoreactive basket cell terminals. Reduction of GABA release from these terminals is the likely mechanism by which both endogenous and exogenous CB1 ligands interfere with hippocampal network oscillations and associated cognitive functions.