Blood
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Interaction of tissue plasminogen activator (t-PA) with fibrin plays a key role in regulation of plasminogen activation and clot dissolution. Previous investigations of t-PA-fibrin interaction, using incorporation of t-PA into polymerizing fibrin clots, have suggested that no significant differences exist in the binding of one-chain or two-chain t-PA to non-cross-linked or cross-linked fibrin. In the present study, binding of 125I-labeled and affinity-purified one-chain and two-chain forms of t-PA to preformed non-cross-linked or cross-linked, sonicated suspension of fibrin was investigated. ⋯ The cleavage of one-chain t-PA to two-chain t-PA allows to bind to a large number of low-affinity binding sites on fibrin. Cross-linking of fibrin by factor XIIIa results in masking of high-affinity binding sites that are present in non-cross-linked fibrin. We propose that both plasmin and factor XIIIa play an important regulatory role in dissolution of blood clots by modulating t-PA-fibrin interaction.
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We investigated the activation of the nonenzymatic protein cofactors factor VIII and factor V in plasma when coagulation was initiated by thromboplastin. With sensitive bioassays, we were able to measure specifically the generation of activated factor VIII and activated factor V in plasma. Our results showed that when plasma was triggered with a relatively high concentration of thromboplastin, factor VIII and factor V were completely activated at the clotting time of plasma. ⋯ In addition, generation of factor VIIIa correlated with thrombin generation and not with factor Xa generation. Furthermore, addition of large amounts of factor Xa to hirudinized plasma did not show detectable factor VIII or factor V activation. We concluded that in plasma activated with thromboplastin the enzyme responsible for activation of factor V and factor VIII is thrombin, not factor Xa.
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T cells are known to interact cooperatively with monocytes to produce Colony-Stimulating Factors (CSF), although T cell-mediated signals leading to CSF secretion by monocytes are not completely understood. We have made use of Northern blot hybridization and specific bioassays to study the effects of the T cell product interleukin-4 (IL-4) on monocyte CSF expression. The results suggest a previously unrecognized role of IL-4 as a CSF inducer since exposure of monocytes to IL-4 resulted in accumulation of transcripts for granulocyte-CSF (G-CSF) and macrophage-CSF (M-CSF). Consequently, IL-4-activated monocytes released factors in their culture supernatants biologically and antigenically indistinguishable from G- and M-CSF.
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Comparative Study
Quantification of plasma factor XIIa-Cl(-)-inhibitor and kallikrein-Cl(-)-inhibitor complexes in sepsis.
Considerable evidence indicates that activation of the contact system of intrinsic coagulation plays a role in the pathogenesis of septic shock. To monitor contact activation in patients with sepsis, we developed highly sensitive radioimmunoassays (RIAs) for factor XIIa-Cl(-)-inhibitor (Cl(-)-Inh) and kallikrein-Cl(-)-Inh complexes using a monoclonal antibody (MoAb Kok 12) that binds to a neodeterminant exposed on both complexed and cleaved Cl(-)-Inh. Plasma samples were serially collected from 48 patients admitted to the intensive care unit because of severe sepsis. ⋯ No significant differences in plasma kallikrein-Cl(-)-Inh or prekallikrein antigen were found between these patients' groups. Elevated Cl(-)-Inh complex levels were measured less frequently in serial samples from patients with septic shock than in those from patients without shock (P less than .0001). Based on these results, we conclude that plasma Cl(-)-Inh complex levels during sepsis may not properly reflect the extent of contact activation.
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The CD11b (Mol) molecule is a member of a family of surface glycoproteins that are essential for adhesion-dependent granulocyte functions. Brief exposure of granulocytes to human granulocyte-macrophage colony-stimulating factor (GM-CSF) in vitro increases the surface expression of CD11b and increases granulocyte adhesiveness. To assess the possible in vivo significance of these observations we studied the effect of GM-CSF on CD11b, CD11a (LFA-1), and CD11c (gp 150, 95) expression on granulocytes from nine adult patients with sarcoma who were receiving GM-CSF as part of a phase I trial. ⋯ Fluorescence-activated cell sorting of granulocytes into high- and low-density CD11b-positive groups revealed a preponderance of immature myeloid forms in the low-density CD11b fraction, which suggests that the late decrease in CD11b expression in some patients may be related to a greater proportion of circulating immature myeloid forms in the peripheral blood. This study suggests that GM-CSF administered as a continuous infusion rapidly upregulates the expression of granulocyte CD11b in vivo. The influence of this phenomenon on in vivo granulocyte aggregation may be clinically relevant with regard to the toxicity of GM-CSF and deserves further investigation.