Antifibrinogen IgG, fibrinogen, and Clq complexes circulating in a hypodysfibrinogenemic proband. Isolation, stoichiometry, and partial characterization

Circulating antifibrinogen antibodies have been reported in rare afibrinogenemic propositi, apparently occurring following fibrinogen replacement therapy, but immune complexes have not been described. In this report we describe circulating immune complexes formed by a monoclonal antifibrinogen IgG in a heterozygous hypodysfibrinogenemic (A alpha 16 Arg-->Cys) proband. Estimated by partial protein sequence and by other analyses, each immune complex consisted of one fibrin(ogen), one C1q, and 3-4 IgG molecules. The complexes were cryoprecipitable, a property also displayed by mixtures of proband IgG and normal fibrinogen. Indicating that both D and E domains were necessary for this behavior, cryoprecipitability was abolished by preincubation of the isolated IgG with either isolated normal fibrinogen fragment D100 or E. Consistent with the crossreactivity of the IgG with normal and mutant fibrinogen, the results suggest that the primary epitope resides on a D-E locus on the fibrin polymer formed by normal and abnormal molecules containing the uncleaved (or mutant) peptide A.

Defensin promotes the binding of lipoprotein(a) to vascular matrix

Retention of lipoproteins within the vasculature is a central event in the pathogenesis of atherosclerosis. However, the signals that mediate this process are only partially understood. Prompted by putative links between inflammation and atherosclerosis, we previously reported that alpha-defensins released by neutrophils are present in human atherosclerotic lesions and promote the binding of lipoprotein(a) [Lp(a)] to vascular cells without a concomitant increase in degradation. We have now tested the hypothesis that this accumulation results from the propensity of defensin to form stable complexes with Lp(a) that divert the lipoprotein from its normal cellular degradative pathways to the extracellular matrix (ECM). In accord with this hypothesis, defensin stimulated the binding of Lp(a) to vascular matrices approximately 40-fold and binding of the reactants to the matrix was essentially irreversible. Defensin formed stable, multivalent complexes with Lp(a) and with its components, apoprotein (a) and low-density lipoprotein (LDL), as assessed by optical biosensor analysis, gel filtration, and immunoelectron microscopy. Binding of defensin/Lp(a) complexes to matrix was inhibited (>90%) by heparin and by antibodies to fibronectin (>70%), but not by antibodies to vitronectin or thrombospondin. Defensin increased the binding of Lp(a) (10 nmol/L) to purified fibronectin more than 30-fold. Whereas defensin and Lp(a) readily traversed the endothelial cell membranes individually, defensin/Lp(a) complexes lodged on the cell surface. These studies demonstrate that alpha-defensins released from activated or senescent neutrophils stimulate the binding of an atherogenic lipoprotein to the ECM of endothelial cells, a process that may contribute to lipoprotein accumulation in atherosclerotic lesions.

The myosin filament XIV backbone structure

The substructure of the thick filaments of chemically skinned chicken pectoralis muscle was investigated by electron microscopy. Images of transverse sections of the myosin filaments were determined to have threefold symmetry by cross-correlation analysis, which gives an unbiased determination of the rotational symmetry of the images. Resolution, using the phase residual test (Frank et al. 1981. Science [Wash. DC]. 214:1353-1355), was found to be between 3.2 and 3.6 nm. Three arrangements of nine subfilaments in the backbone were found in all regions of the filament at ionic strengths of 20 and 200 mM. In the average images of two of these, there were three dense central subfilaments and three pairs of subfilaments on the surface of the thick filament. In the average image of the third arrangement, all of the protein mass of the nine subfilaments was on the surface of the filament with three of them showing less variation in position than the others. A fourth arrangement appearing to be transitional between two of these was seen often at 200 mM ionic strength and only rarely at 20 mM. On average, the myosin subfilaments were parallel to the long axis of the filament. The different arrangements of subfilaments appear to be randomly distributed among the filaments in a transverse section of the A-band. Relative rotational orientations with respect to the hexagonal filament lattice, using the three densest subfilaments as reference showed a major clustering (32%) of filaments within one 10 degrees spread, a lesser clustering (15%) at 90 degrees to the first, and the remainder scattered thinly over the rest of the 120 degrees range. There was no obvious pattern of distribution of the two predominant orientations that could define a superlattice in the filament lattice.

Electron microscope investigation of the early stages of fibrin assembly. Twisted protofibrils and fibers

Structures formed during the early stages of clot formation have been produced in a controlled manner by polymerization of soluble fibrin monomers prepared from dissolved normal clots that had been formed upon addition of thrombin to fibrinogen. In agreement with other studies using different approaches, electron microscopy of negatively contrasted or rotary-shadowed specimens of these preparations reveal two-stranded protofibrils, as well as shorter oligomers and fibrin monomers. Individual fibrin molecules are similar in appearance to fibrinogen, suggesting that no large-scale changes in conformation occur on removal of the fibrinopeptides. Moreover, these micrographs show details of the protofibril structure not previously seen. The visualization of clear cross-over points of the filaments making up the protofibril indicate that these structures are twisted. Diffraction patterns of electron micrographs of both protofibrils and fibers and computer modeling of protofibrils also suggest that these structures are twisted but not precisely ordered.

The myosin filament. X. Observation of nine subfilaments in transverse sections

The molecular packing of the subfilaments in muscle thick filaments has been investigated by electron microscopy. Thin (80-100 nm) transverse sections of vertebrate skeletal muscle were cut, and 129 electron microscope images of thick filaments from 15 different areas including seven to ten images in each area were analyzed by computer image processing. The transverse sections were limited to the portion of the filaments between the bare zone and the C-protein bearing region. Of the 129 images, six were discarded because they were structurally disrupted, 17 did not show evidence for the presence of subfilaments from the autocorrelation function, and four did not show evidence for three-fold rotational symmetry from the power spectrum. The remaining 102 filaments all showed evidence for three-fold rotational symmetry, consistent with other available evidence (Pepe, 1982). From the analysis of these images by rotational filtering, we have found that the vertebrate skeletal myosin filament is made up of nine subfilaments and that the image appears to have trigonal symmetry. Of these subfilaments, six are arranged with a center-to-center spacing of about 4 nm and the other three on the surface of the filament are distorted from this arrangement. Three additional densities, which together with the other nine, correspond to the pattern of 12 densities previously observed in more highly selected images (Stewart et al., 1981; Pepe and Drucker, 1972) were observed in 5% of the images. Another pattern of nine subfilaments peripherally arranged around the circumference of the filament was observed occasionally. This latter image may represent the organization of the subfilaments in the bare zone region of the filament, resulting from sampling of individual filaments displaced longitudinally relative to the other filaments in the A-band.

Comparison of the accuracy of the Binkhorst, Colenbrander, and SRK implant power prediction formulas

The prediction accuracy of the Binkhorst, Colenbrander, and SRK formulas were compared in five series from different sources totalling 654 cases. The SRK formula was superior to both the other formulas by having a smaller average error per case, a smaller range of error from highest minus to highest plus, and a smaller proportion of cases with greater than 2 diopters (D) of error in all five series studied. In four of the five series, the SRK formula also had the greatest proportion of cases with less than 1 D of error. The Colenbrander formula was superior to the Binkhorst formula in all five series with regard to average error, proportion of cases with less than 1 D of error, and proportion of cases with more than 2 D of error. The range of error from highest minus to highest plus was equivalent with the two formulas. All available published literature on the accuracy of implant power prediction formulas was reviewed and appears to support our findings.