No association of complement mannose-binding lectin deficiency with cardiovascular disease in patients with Systemic Lupus Erythematosus.

Cardiovascular (CV) morbidity is the major cause of death in patients with Systemic Lupus Erythematosus (SLE). Previous studies on mannose-binding lectin (MBL) gene polymorphisms in SLE patients suggest that low levels of complement MBL are associated with cardiovascular disease (CVD). However, as large studies on MBL deficiency based on resulting MBL plasma concentrations are lacking, the aim of our study was to analyze the association of MBL concentrations with CVD in SLE patients. Plasma MBL levels SLE patients included in the Swiss SLE Cohort Study were quantified by ELISA. Five different CV organ manifestations were documented. Of 373 included patients (85.5% female) 62 patients had at least one CV manifestation. Patients with MBL deficiency (levels below 500 ng/ml or 1000 ng/ml) had no significantly increased frequency of CVD (19.4% vs. 15.2%, P = 0.3 or 17.7% vs. 15.7%, P = 0.7). After adjustment for traditional CV risk factors, MBL levels and positive antiphospholipid serology (APL+) a significant association of CVD with age, hypertension, disease duration and APL+ was demonstrated. In our study of a large cohort of patients with SLE, we could not confirm previous studies suggesting MBL deficiency to be associated with an increased risk for CVD.

Human blood platelet secretion: optical multichannel analyzer measurements using acriflavine as a release indicator.

Blood platelets preloaded with the fluorescent amine acriflavine release the trapped fluorophore after stimulation with thrombin or the divalent cation ionophore A23187. Release was detected by an increase in acriflavine fluorescence, which is otherwise strongly quenched in the platelet, by using an optical multichannel analyzer to monitor the spectral and temporal reaction parameters. The secretion of [14C]serotonin and acriflavine is well correlated, suggesting that acriflavine, like serotonin and the closely related fluorescent drugs mepacrine and acridine orange, is accumulated in and released from platelet dense bodies. Acriflavine secretion at 37 degrees C in the absence of external calcium is characterized by a short delay, followed by a rapid biphasic increase in fluorescence that implies at least a three-stage secretory process. For saturating levels of thrombin the delay was 1.5 s and release was 90% complete within 6-7 s. The delay could not be shortened by prestimulation under conditions that induce shape changes but not release, i.e., with ADP, arachidonic acid, or low levels of thrombin or A23187. Acriflavine secretion induced by A23187 was similar but less effective; the reaction was slower, the yield was smaller, and, in contrast to thrombin, the longer lag period could be significantly shortened by prestimulation.

Optical shape change analysis in stirred and unstirred human platelet suspensions. A comparison of aggregometric and stopped-flow turbidimetric measurements.

To monitor the discoidity of platelets in an aggregometer, a relative, stirring-dependent change in extinction (delta ES) is defined. delta ES is large in highly discoid and small in ADP-activated platelets. The platelet shape change, as monitored by the changes in delta ES, not only precedes ADP-induced aggregation but also outlasts disaggregation. In unstirred samples, ADP induces insignificant changes in extinction in the aggregometer but biphasic changes in extinction in a "zero degree" stopped-flow turbidimeter. This discrepancy apparently arises from differences in the amount of scattered light collected by the optical systems and from wavelength-dependent differences in sensitivity. Similar progress curves were observed in both instruments for the biphasic changes in extinction which accompany the release reaction induced by thrombin or concanavalin A in pre-sphered platelets. The aggregometer is advantageous for monitoring rheooptical effects of the asymmetric platelets while the stopped-flow laser turbidimeter is superior in quantifying the changes in extinction according to the light scattering theory.

Optimal efficiency of human platelet shape changes.

The light scattering extinction coefficients and kinetic rate constant(s) for the disc to sphere and the sphere to (smaller) 'spiny sphere' shape changes induced in platelets by saturating amounts of ADP are compared at 31, 37 and 41 degrees C. Platelets exhibit optimum efficiency at 37 degrees C, as judged by not only the rates of the shape changes but also by alterations in the overall sizes and shapes of the three platelet forms. Unstimulated (discoid) platelets appear to be flatter at 37 degrees C, the disc to sphere reaction appears to be impaired at other than 37 degrees C, and the pseudopodia which characterize the final spiny sphere may be more prominent at 41 degrees C.

Transient kinetics of the rapid shape change of unstirred human blood platelets stimulated with ADP.

Unstirred (isotropic) suspensions of human blood platelets stimulated with ADP in a stopped-flow laser turbidimeter exhibit a distinct extinction maximum during the course of the classical rapid conversion of initially smooth flat discoid cells to smaller-body spiny spheres. This implies the existence of a transient intermediate having a larger average light scattering cross section (extinction coefficient) than either the disc or the spiny sphere. Monophasic extinction increases reaching the same final value were observed when either discoid or spiny sphere platelets were converted to smooth spheres by treatment with chlorpromazine, and sphering of discoid cells was accompanied by a larger total extinction change than the retraction of pseudopods by already spherical cells. These and other results suggest that the ADP-induced transient state represents platelets that are approximately as "spherical" as the irregular spiny sphere but lack the characteristic long pseudopods and as a consequence are larger bodied. Fitting the ADP progress curves to the series reaction A leads to B leads to C by means of the light scattering equivalent of the Beer-Lambert law yielded scattering cross sections that are consistent with this explanation. The rate constants for the two reaction steps were identical, indicating that ADP activation corresponds to a continuous random (Poisson) process with successive apparent states "disc," "sphere," and "spiny sphere," whose individual probabilities are determined by a single rate-limiting step.