Objective Systemic lupus erythematosus (SLE) is associated with the premature development of cardiovascular disease. The platelet–endothelium interaction is important in the pathogenesis of cardiovascular disease. In this study, we investigated the platelet phenotype from patients with SLE and matched controls, and their effect on endothelial cells. Approach and Results Platelet aggregability was measured in 54 SLE subjects off antiplatelet therapy (mean age 40.1±12.8 years; 82% female; 37% white) with age- and sex-matched controls. Platelets were coincubated with human umbilical vein endothelial cells (HUVECs) and changes to gene expression assessed by an RNA array and quantitative reverse transcription polymerase chain reaction. SLE disease activity index ranged from 0 to 22 (mean 5.1±3.9). Compared with controls, patients with SLE had significantly increased monocyte and leukocyte–platelet aggregation and platelet aggregation in response to submaximal agonist stimulation. An agnostic microarray of HUVECs cocultured with SLE platelets found a platelet-mediated effect on endothelial gene pathways involved in cell activation. Sera from SLE versus control subjects significantly increased (1) activation of control platelets; (2) platelet adhesion to HUVECs; (3) platelet-induced HUVEC gene expression of interleukin-8, and intercellular adhesion molecule 1; and (4) proinflammatory gene expression in HUVECs, mediated by interleukin-1β–dependent pathway. Incubation of SLE-activated platelets with an interleukin-1β–neutralizing antibody or HUVECs pretreated with interleukin-1 receptor antibodies attenuated the platelet-mediated activation of endothelial cells. Conclusions Platelet activity measurements and subsequent interleukin-1β–dependent activation of the endothelium are increased in subjects with SLE. Platelet–endothelial interactions may play a role in the pathogenesis of cardiovascular disease in patients with SLE.

Abnormalities of platelet aggregation in response to adenosine diphosphate in 56 patients with chronic liver disease correlated with impairment of hepatocellular function but not with the etiology of the liver disease. Platelet-poor plasma from some patients appeared to contain an inhibitor since, in cross-over studies, it reduced the degree of aggregation of control subjects. However, platelet-poor plasma from some other patients enhanced aggregation in controls, and this was thought to be due to the presence of fibrin monomer. In the majority of patients with severe liver disease, platelet function still appeared defective, even after exclusion of the effects of plasma, and was independent of the platelet count in peripheral venous blood. Since patient platelet volumes were smaller than those of controls, these findings might be explained by deficiency of the larger hemostatically active type of platelet as a consequence of either bone marrow failure or splenic sequestration.

SUMMARY In 34 patients with fulminant hepatic failure, platelets, in addition to being reduced in numbers, were smaller than those of healthy controls. In keeping with this, capillary bleeding times were significantly longer than could be accounted for by reduction in numbers alone. In a small group of these patients use of charcoal haemoperfusion for temporary liver support produced a doubling of the capillary bleeding time despite only a small drop in arterial platelet counts. This disproportionate prolongation of bleeding time was almost certainly caused by the loss of larger platelets in the charcoal columns during perfusion, as the mean median volume also fell during perfusion. Rises in screen filtration pressure of the blood leaving the columns were found during some perfusions and thought to be indicative of platelet aggregates. Release of vasoactive substances from platelets could account for the hypotension often found at this time.

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The biocompatibility of two commercially available charcoal columns, one containing coated and the other uncoated but immobilized charcoal, was compared during four haemoperfusions with each in eight healthy greyhounds. Reductions in arterial levels of platelets (49% and 42% respectively) and leucocytes (both 21%) were similar. Microaggregates, detected by the Swank screen filtration pressure technique, were found in blood leaving the columns during three of the four perfusions with each column. Another twelve perfusions with the uncoated column were carried out with the addition of one or other of the following three agents which inhibit platelet aggregation: sulfinpyrazone, dipyridamole, or citrate-phosphate-dextrose. With none of these were platelet losses less as compared with the four perfusions in which heparin only was used. However, rises in screen filtration pressure were less pronounced. In other perfusions, where its dosage was varied, heparin was shown to reverse, and in large doses delay, the appearance of micro-aggregates. Thrombus in the column itself may be a source of microaggregates, but platelet aggregation in the absence of thrombus deposition may be responsible. The relation of these findings to micro-aggregate formation, which has constituted a clinical problem during charcoal haemoperfusion in humans with fulminant hepatic failure, is considered.