Effects of the cell adhesion peptide, Arg-Gly-Asp-Ser, on responses of washed platelets from humans, rabbits, and rats

Fibrinogen is a cofactor in the aggregation of human platelets, and is required for ADP-induced aggregation of washed platelets; however, exogenous fibrinogen is not required for ADP-induced aggregation of washed platelets from rabbits or rats. Because with human platelets the cell adhesion peptide, Arg-Gly-Asp-Ser (RGDS), inhibits aggregation and the binding of 125I-fibrinogen to ADP-stimulated platelets, its effects on rabbit and rat platelets were studied to investigate the differences in the fibrinogen requirements of platelets from the three species. RGDS (50 mumol/L) caused greater than 80% inhibition of thrombin- induced or (ADP + fibrinogen)-induced aggregation of human platelets, but only 3% to 9% inhibition of the aggregation of rabbit or rat platelets, regardless of whether fibrinogen was added. RGDS inhibited the binding of 125I-fibrinogen to ADP-stimulated human platelets by 80% to 90%, but by only 15% to 27% in the case of rabbit or rat platelets. The differences were due to the species of platelets, since human and rabbit fibrinogens gave similar results. In addition, RGDS failed to displace fibrinogen from the surface of rabbit platelets that had been stimulated with ADP. Thus, there are species differences in the ability of the cell adhesion peptide, RGDS, to block the platelet fibrinogen receptor, even within the mammalian species.     

Neutrophil elastase produces 52-kD and 30-kD glucocorticoid receptor fragments in the cytosol of human leukemia cells

Characterization of glucocorticoid receptors in leukemia cells is important to understand mechanisms of glucocorticoid resistance but has been impeded by receptor fragmentation in cytosol extracts. We recently found that formation of 52- and 30-kilodalton (kD) glucocorticoid receptor fragments in cytosol of leukemia cells is due to proteolysis and is blocked by diisopropylfluorophosphate (DFP). In the present study, we identify a 28-kD serine protease in cytosol of leukemia cells that binds [3H]DFP and correlates with the formation of 52- and 30-kD receptor fragments. This protease is immunoprecipitated by antiserum to neutrophil elastase. Limited digestion of [3H]dexamethasone-21-mesylate- labeled receptors by purified neutrophil elastase produces 52- and 30- kD receptor fragments. Receptor fragmentation in the cytosol of leukemia cells in inhibited by methoxysuccinyl-alanyl-alanyl-prolyl- valyl-chloromethylketone, a highly specific inhibitor of neutrophil elastase. The addition of as few as 5% neutrophils to a lymphoid cell suspension provides sufficient elastase to produce receptor fragmentation. Our findings indicate that neutrophil elastase is responsible for receptor fragmentation in the cytosol of leukemia cells. The neutrophil elastase may be endogenous to the leukemia cells or may come from neutrophils that contaminate leukemia cell suspensions.     

Demonstration of a blood-bone marrow barrier to macrophage colony- stimulating factor

Several previous studies suggested that murine macrophage colony- stimulating factor (CSF-1) might have impaired access to hematopoietic cells in the marrow. The apparent lack of hematopoietic responses to exogenous CSF and the finding of available or unoccupied CSF receptors despite saturating CSF levels in the serum led to studies of a potential blood-bone marrow barrier for this factor. Groups of mice were injected with pure unlabeled CSF-1 by either intravenous (IV) or intraperitoneal (IP) routes. Marrow and spleen cells were obtained at intervals after injection, held at 0 degree C, and assessed for changes in binding of 125I-CSF. Saturation of all available CSF receptors is achieved in vitro with 100 to 150 U CSF/mL. Despite achieving serum levels of 5,000 to 7,000 U/mL after IV injection of 25,000 units of CSF, less than 50% of the marrow receptors and less than 85% of the splenic receptors were saturated or downregulated. The decline in receptor availability was transient, with return of receptor sites in two to four hours. Increasing the IV dose to 125,000 units increased serum CSF values to approximately 20,000 U/mL and led to a virtual disappearance of available receptors for two to three hours. When administered IP, only approximately 40% of marrow and 80% of splenic receptors were affected for two hours. It was necessary to increase the dose of CSF to 250,000 units IP to saturate or downregulate receptors for three to four hours after injection. These observations indicate a marked blood-bone marrow barrier and lesser blood-spleen barrier for the transfer of serum CSF to responsive hematopoietic cells in vivo.     

Hepatic parenchymal gas after blunt trauma

Hepatic parenchymal gas was demonstrated by computed tomography in a boy who had sustained severe blunt trauma to the abdomen 12 hours earlier. There was no clinical evidence of infection. Although previous reports have suggested that hepatic parenchymal gas indicates the presence of infection, such gas may also be a manifestation of severe blunt trauma without infection.     

Cystic fibrosis and the phenotypic expression of autosomal dominant polycystic kidney disease

Recent experiments in cultured cyst epithelial cells from kidneys of patients with autosomal dominant polycystic kidney disease (ADPKD) have shown that the cystic fibrosis (CF) transmembrane conductance regulator (CFTR) is present in the apical surface of these cells and mediates chloride (Cl-) and fluid secretion in vitro. To determine whether the presence of CF with the expression of mutated CFTR proteins modifies cyst formation in ADPKD, we studied a large family with both inherited diseases. ADPKD in this family is linked to PKD1. The family is composed of 26 members; 11 members with ADPKD, 4 members with CF, and 2 members with both diseases. Renal volumes measured by computerized tomography (CT), calculated creatinine clearances, and other clinical parameters in the family members with ADPKD and CF were compared with those in the family members with ADPKD alone, as well as to a large population of patients with ADPKD. The patients with CF and ADPKD, but not the CF heterozygote carriers with ADPKD, had less severe polycystic kidney and liver disease, as indicated by normal renal function; smaller renal volume, even when corrected for height and body surface area; and the absence of hypertension and liver cysts. These observations suggest that the coexistence of CF may reduce the severity of ADPKD.     

HIV/AIDS infection control enforcement: a comparison between Nigeria and the United States

We examined differences in approaches to HIV-related infection control practices in two university teaching hospitals in the United States and Nigeria. Health care workers (n = 202 in Nigeria and 186 in the USA) responded to a previously validated measure of infection control practices. There were significant differences in the estimated probability of treating a person with HIV disease (higher in USA), and a greater probability of peer ridicule as a way of enforcing group norms on infection control in Nigeria. Peer enforcement of norms was significantly lower in the USA. In both countries, more precautions would be taken if it was known that the patient was HIV infected. Infection control practices were more likely to be followed in the USA compared with Nigeria if they were praised for this activity, if appropriate facilities (sharps containers, gloves, etc.) were nearby, and if they felt that infection control procedures were effective. These data point to the importance of normative social pressures in Nigeria and of knowing the patient is HIV infected in the USA and feeling that infection control procedures are effective ways of avoiding occupational HIV infection. The role of normative pressures and assumptions about HIV infection status as well as cues and availability of facilities for infection control appear to differ between these health care workers in Nigeria and the USA.