Human fibroblast tissue factor is inhibited by lipoprotein-associated coagulation inhibitor and placental anticoagulant protein but not by apolipoprotein A-II

Studies of proteins that inhibit tissue factor activity have generally been conducted using either an extracted tissue homogenate ("thromboplastin") or tissue factor protein reconstituted into phospholipid vesicles rather than with tissue factor expressed in cell membranes (its physiological environment). In the present study, a human fibroblast cell strain was used to evaluate the effects of lipoprotein associated coagulation inhibitor (LACI), placental anticoagulant protein (PAP), and apolipoprotein A-II (apo A-II) on human tissue factor in cell membranes. LACI was tested from 7.8 to 500 pmol/L on fibroblasts cultured at cell densities ranging from 3,500 to 9,925 cells/well, and caused a progressive inhibition of tissue factor activity. PAP was tested from 3.9 nmol/L to 1 mumol/L at cell densities ranging from 4,500 to 15,400 cells/well and caused up to 83% inhibition of tissue factor activity. Inhibition by these proteins appeared to be influenced by cell density as well as whether the cells were intact or disrupted. Apo A-II, up to 1 mumol/L, did not inhibit the tissue factor activity of intact or disrupted fibroblasts at any cell density examined even though it did inhibit the activity of tissue factor in phospholipid vesicles. Of these inhibitors of tissue factor-dependent activation of factor X, LACI was the most effective in suppressing the generation of factor Xa activity. The effects obtained with apo A-II are clearly dependent on the nature of the tissue factor preparation with which it is tested. The disparity between the inhibitory effect of apo A-II on the activity of tissue factor reconstituted into lipid vesicles and the absence of effect on the activity of tissue factor remaining in cell membranes serves to reemphasize the necessity of reexamining results obtained with model systems using as nearly physiological reagents as possible.     

Visceral target organs in systemic St. Louis encephalitis virus infection of hamsters

Ultrastructural aspects of St. Louis encephalitis virus infection of the major extraneutral organs and tissues of suckling hamsters were examined. In the pancreas, both the exocrine and endocrine portions were equally affected by the virus. A feature apparently unique to flaviviruses was the accumulation of virus particles in all types of secretory granules in this organ. Virus particles were seen within myocardial fibers and within the smooth muscle cells and endothelial cells of small blood vessels of the heart. In the intestines, the lamina propria was the most severely infected, with virus particles accumulated in all cell types.     

The functional activities of IgG and IgM anti-A and anti-B

The rate constants for association and dissociation, and the equilibrium constants, were determined for ¹²⁵I-labelled anti-A and anti-B of both IgG and IgM molecular types. The following results and conclusions were obtained:

1. The equilibrium constants were within the range 06×10⁸–13.0×10⁸ l/mole, and were of the same order for both IgG and IgM antibodies.

2. The initial rate constants for association were in the range 2.1×10⁵–4.8×10⁵ l/mole/sec, and the energy of activation (E_a) 6700–9000 cal/mole. These results indicate that the rate of association is approaching the limit set by the rate of diffusion of the reactants.

3. The initial rate constants for dissociation were 1 × 10^-4–5 × 10^-4/sec and E_a = 20,000–36,000 cal/mole. These latter values suggest that more than one bond must be broken simultaneously during dissociation.

4. Ionic strength and pH changes have only a minor effect on the constants; this indicates absence of ionic groups on A and B antigen sites.

5. The changes in enthalpy were –5400 to –21,800 cal/mole; the reactions are mainly enthalpy driven and this accounts for the fact that anti-A and anti-B agglutination titres increase as the temperature is decresed.

6. There was heterogeneity of the values of the standard change in free energy, enthalpy and entropy within each example of antibody.

7. The approximate concentrations of antibody at the end-points of the agglutination titres were: for IgG antibody, 0.2 μg/ml; for IgM antibody, 0.01 μg/ml.

     

Comparison of a modified microagglutination technique for HBsAg with the standard technique and a new RIA system.

A further modification of the standard RPHA technique (Hepatest, Wellcome Reagents) for the detection of HBsAg is described. This modification does not require a centrifugation step which is required by the other modifications that have been described previously and consequently takes a little longer to perform. It does, however, retain the advantages of increased sensitivity and decreased costs which are also features of the other modifications. A series of 939 routine clinical specimens were used to evaluate the method described and to evaluate a new RIA kit for the detection of HBsAg (Hepatube, Wellcome Reagents). Of 53 specimens found to be positive for HBsAg by RIA, 50 (94% were detected by the modified Hepatest RPHA as opposed to 47 (89%) by the standard technique.     

Inclusion of satellites in an 18/21 translocation chromosome shown by ammonical-silver staining (sat-banding) in case of partial trisomy 18.

A male infant with a partial trisomy 18 and a 46,XY, --21, t(18;21)(18qter replaced by 18q12::21 p13 replaced by 21 qter) chromosome complement is described. The translocation chromosome is of special interest because it includes the satellites of chromosome 21. This was shown by differential satellite staining with the ammoniacal-silver technique.     

Serial linkage of target selection for orienting and tracking eye movements

Many natural actions require the coordination of two different kinds of movements. How are targets chosen under these circumstances: do central commands instruct different movement systems in parallel, or does the execution of one movement activate a serial chain that automatically chooses targets for the other movement? We examined a natural eye tracking action that consists of orienting saccades and tracking smooth pursuit eye movements, and found strong physiological evidence for a serial strategy. Monkeys chose freely between two identical spots that appeared at different sites in the visual field and moved in orthogonal directions. If a saccade was evoked to one of the moving targets by microstimulation in either the frontal eye field (FEF) or the superior colliculus (SC), then the same target was automatically chosen for pursuit. Our results imply that the neural signals responsible for saccade execution can also act as an internal command of target choice for other movement systems.