Biomedical subjects
Publications and source records attributed to A W Simpson.
Experiments using human monocytes and the yeast Saccharomyces cerevisiae have shown that fibronectin is a major plasma opsonin. Further studies have shown that fibronectin promotes the ingestion as well as the adherence of micro-organisms. These observations are independent of the non-physiological concentrations of heparin used in other assay systems.
Previous bioassays for studying the opsonic regulation of the monocyte-macrophage system are subject to a variety of serious disadvantages which limit their value. An assay system is described which avoids many of these pitfalls and is applicable to the rapid assay of large numbers of samples. Human monocytes were isolated from peripheral blood and Saccharomyces cerevisiae used as the target particle. Particle ingestion was assessed using an electronic particle size analyzer and a close correlation was shown between this assay and a visual assessment of ingested micro-organisms.
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The diadenosine polyphosphates are a group of long-lasting compounds, released into the bloodstream by platelet degranulation. They mediate endothelium-dependent vasodilatation in several animal vascular systems via P2Y receptors coupled to increases in cytoplasmic calcium ([Ca(2+)](c)). However, there is little evidence of diadenosine-mediated vasodilatation in the human vasculature, and a direct interaction with natively expressed P2Y receptors on human endothelium has not been demonstrated. We have therefore studied the effects of diadenosines on primary cultures of human saphenous vein endothelial cells (HSVECs) and related this to the expression of P2Y receptors. HSVECs were loaded with the calcium-sensitive dye fura-2, and nucleotide-stimulated [Ca(2+)](c) responses were recorded. HSVECs responded to 10 microM UTP, ATP and 2-methylthio-ATP but not to UDP. Consistent with the recorded [Ca(2+)](c) responses, RT-PCR analysis of HSVEC RNA amplified specific products for the P2Y(1) and P2Y(2) receptors but not the P2Y(4) and P2Y(6) receptors. HSVECs responded to Ap(3)A with a rise in [Ca(2+)](c), but none of the other diadenosines tested elicited a response. Therefore natively expressed human P2Y(1) and P2Y(2) receptors are insensitive to diadenosine polyphosphates with the exception of Ap(3)A. We would therefore predict that the diadenosine polyphosphates have only a limited vasodilatory role in human saphenous veins.