Expression of alpha IIb beta 3 integrin (GPIIb-IIIa) in myeloid cell lines and normal CD34+/CD33+ bone marrow cells.

Regulation of myeloid cell proliferation and differentiation in the bone marrow is mediated, in part, by the interaction of integrins on early myeloid cells with the extracellular matrix proteins secreted by stromal cells. To further define adhesive protein receptors of early myeloid cells, we examined the expression of the integrin GPIIb-IIIa (alphaIIbbeta3) in leukemic cell lines KG-1a, KG-1, and HL-60, that represent early stages of myeloid differentiation. All three cell lines expressed surface GPIIb-IIIa as measured by flow cytometry and by binding of 125I-anti-GPIIb-IIIa monoclonal antibody. Preincubation of cells with human AB serum or platelet releasate increased GPIIb-IIIa surface expression. GPIIb transcripts were identified in all three cell lines by Northern blot analysis. Furthermore, we readily detected GPIIb transcripts in fluorescence activated cell sorted (FACS) myeloid cells from normal human bone marrow by RT-PCR. Cloning and sequencing of the PCR products established the identity of GPIIb transcripts in the leukemic cell lines and CD34+/CD33+ normal bone marrow cells. Since the normal myeloid cells also demonstrated markers corresponding to the maturational stage of KG-1a/KG-1 cells, we propose that GPIIb-IIIa may serve as a myeloid differentiation antigen and as a key integrin of myeloid precursors.

Selective induction of a glycoprotein IIIa ligand-induced binding site by fibrinogen and von Willebrand factor.

Ligand-induced binding sites (LIBS) are neoantigenic regions of glycoprotein (GP)IIb-IIIa that are exposed upon interaction of the receptor with the ligand fibrinogen or the ligand recognition sequence (RGDS). LIBS have been suggested to contribute to postreceptor occupancy events such as full-scale platelet aggregation, adhesion to collagen, and clot retraction. This study examined the induction requirements of a GPIIIa LIBS with regard to ligand specificity. Through the use of the anti-LIBS D3, we report that this complex-activating antibody induces fibrinogen- and von Willebrand factor-binding to GPIIb-IIIa on intact platelets. Bound ligand was detected by flow cytometric analysis and platelet aggregation assays. These bound ligands increased the number of D3-binding sites and altered the affinity of D3 for GPIIb-IIIa on platelets. In contrast, activation of platelet GPIIb-IIIa by D3 did not increase the binding of another RGD-containing ligand, vitronectin. Furthermore, bound vitronectin on thrombin-stimulated platelets did not cause the expression of the D3 LIBS epitope. We conclude direct activation of GPIIb-IIIa in the absence of platelet activation results in selective ligand interaction and that D3 LIBS induction requires the binding of the multivalent ligands, fibrinogen or von Willebrand factor. Thus, the region of GPIIIa recognized by D3 may be an important regulatory domain in ligand-receptor interactions that directly mediate platelet aggregation.

Immunological comparisons of integrin alpha IIb beta 3 (GPIIb-IIIa) expressed on platelets and human erythroleukemia cells: evidence for cell specific differences.

Platelet glycoprotein IIb-IIIa (GPIIb-IIIa, alpha IIb beta 3) is expressed on the cell surface of the human erythroleukemia (HEL) cell line. Previous studies have demonstrated differences in GPIIb-IIIa ligand binding properties of HEL cells when compared to platelets. Although the mRNA sequences for GPIIb and GPIIIa are identical in platelets and HEL cells, cell specific differences in the conformation states of the GPIIb-IIIa complex may exist and may explain in part the contrasting functional properties. Two monoclonal antibodies (mAbs), an anti-GPIIb mAb C3 and an anti-GPIIIa mAb D3, were used to determine whether differences in GPIIb-IIIa conformational states could be measured. Initial studies in a purified system showed that the mAbs' binding to isolated GPIIb-IIIa conformers was increased to the active GPIIb-IIIa and to dissociated receptor subunits when compared to the inactive form. Furthermore, soluble active GPIIb-IIIa was a much better inhibitor of D3 binding to the immobilized receptor compared to soluble inactive GPIIb-IIIa. Extending these studies with intact cells, we detected at least two classes of binding sites for each mAb on each cell type. Differences in Bmax and in the relative affinities of the mAbs were identified and may represent subpopulations of GPIIb-IIIa conformations. Total HEL cell and platelet GPIIb-IIIa was determined in our binding assays using a radiolabeled GPIIb-IIIa complex specific mAb, 10E5. HEL cells express approximately five times more GPIIb-IIIa on a per cell basis. The percent of total GPIIb-IIIa that represented each class of mAb binding sites was determined. In summary, the relative differences in GPIIb-IIIa conformation found on platelets and HEL cells may be related to cell-specific ligand binding properties and activation states of the receptor.

Rehabilitation of the edentulous mandible with osseointegrated dental implants: 10 year follow-up.

Long-term retrospective studies on the efficacy of implant retained bridgework are relatively few. In this study, 10 year follow-up results are reported on the rehabilitation of the edentulous mandible with osseointegrated implant anchored bridges. Fifteen patients were closely maintained and monitored using the conventional indices used in longitudinal periodontal research, together with serial intraoral periapical and extraoral panoramic radiographs. The need for prosthetic maintenance and the effects of the treatment on soft tissues, supporting bone, opposing dentition and the behavioural aspects of such rehabilitation are discussed. Based on the reviewed results of the study and numerous other investigations, the treatment of mandibular edentulism with fixed bridges supported by osseointegrated implants ad modum Brånemark is a highly effective method, giving predictable long-term results.

Further characterization of the loop structure of platelet glycoprotein IIIa: partial mapping of functionally significant glycoprotein IIIa epitopes.

Glycoprotein (GP) IIb-IIIa serves as the platelet fibrinogen receptor. Studies of the tertiary structure of GPIIIa have shown that the protein has a large loop structure of at least 325 amino acids in length. To further characterize this loop structure, intact platelets were digested with alpha-chymotrypsin. Digestion products were examined using the anti-GPIIIa monoclonal antibodies (MoAbs) AP3, D3GP3, and C5GP3, as well as the human alloantibody, anti-PLA1. AP3 recognized GPIIIa digestion products of 109, 95, and 68 Kd. D3GP3 and C5GP3 recognized an additional band of 51 Kd. Time course digestions demonstrated that the 51-Kd fragment was generated by proteolysis of the 68-Kd peptide. Sequence analysis of the reduced 51-Kd peptide showed that this fragment began at amino acid 422. The nonreduced 51-Kd peptide was reactive with antibodies directed against the first 13 amino acids of GPIIIa, demonstrating the presence of a covalently attached N-terminal peptide. These data suggest that: (1) the minimum length of the loop structure is at least 384 amino acids; (2) the AP3 epitope is formed at least in part by a determinant contained within residues 348 to 421; and (3) the D3GP3 and C5GP3 epitopes are contained within amino acids 422 to 692 of GPIIIa, a region that may be flexible and involved in conformational changes that occur after ligand binding.

A conformation-dependent epitope of human platelet glycoprotein IIIa.

This study explores conformational states of human platelet glycoprotein IIIa (GP IIIa) and possible mechanisms of fibrinogen receptor exposure. D3GP3 is an IgG1, kappa monoclonal antibody generated against purified GP IIIa and found to be specific for GP IIIa by immunoprecipitation and Western blot analysis. The binding of D3GP3 to resting platelets caused fibrinogen binding (approximately 5,000 molecules/platelet) and platelet aggregation but not secretion. Platelets express 40,000-50,000 GP IIb-IIIa molecules in their surface membranes. However, resting platelets only bound approximately 5,000 D3GP3 molecules/platelet. D3GP3 binding to platelets could be increased 2-3-fold by dissociation of the GP IIb-IIIa complex with 5 mM EDTA or by occupying the fibrinogen receptor with either RGDS peptides or fibrinogen. Platelet stimulation with ADP in the absence of fibrinogen did not cause increased D3GP3 binding above control levels. These data suggest that 1) GP IIb-IIIa can exist in multiple conformations in the platelet membrane, 2) D3GP3 binding to GP IIIa can expose the fibrinogen receptor, 3) the binding of either RGDS peptides or fibrinogen causes exposure of the D3GP3 epitope, and 4) platelet activation in the absence of ligand does not induce the same conformational changes in GP IIb-IIIa as does receptor occupancy by RGDS peptides or fibrinogen.

Calcium mobilization in human platelets using indo-1 and flow cytometry.

Regulation of cytoplasmic free calcium concentration is believed to be important in the response of platelets to external stimuli. A relatively new fluorescent calcium indicator, indo-1, has properties by which alterations of cytoplasmic calcium can be evaluated in single platelets by flow cytometry. Activation of platelets at a temperature lower than 37 degrees C allows examination of the heterogeneity of intracellular free calcium levels and can distinguish variations among platelets in the initiation, duration, and magnitude of calcium fluxes. The clear advantage of flow cytometric analysis of platelet cytosolic calcium is that stimulus-response coupling can now be studied on a single cell basis. Platelets were activated by addition of human alpha-thrombin or ADP at 37 degrees C or at room temperature (22 degrees C). Activation at 37 degrees C approaches more closely an in vivo response and, as expected, increases in cytosolic calcium occurred within seconds of agonist addition. Transient increases in cytoplasmic calcium levels occurred when platelets were challenged with a low concentration of agonist. Heterogeneity in cytoplasmic calcium levels was also observed at 10(-5) mol/L ADP and 0.1 U/mL alpha-thrombin. Some of this heterogeneity was no longer observed at higher concentrations of agonist (10(-4) mol/L ADP and 0.5 U/mL thrombin), suggesting that a sufficient magnitude of signal is required to induce changes in platelet cytosolic calcium. Light-scatter properties of the activated platelets were also monitored simultaneously and showed changes in response to both agonists. The ability to measure changes in cytoplasmic free calcium by ratio flow cytofluorimetry provides a new approach to study of the role of alterations in intracellular calcium in response to agonists acting through different membrane receptors as well as providing a sensitive technique to detect functional subpopulations of platelets.

Clinical and microscopic findings in edentulous patients 3 years after incorporation of osseointegrated implant-supported bridgework.

15 mandibular fixed prostheses supported by osseointegrated titanium implants were examined 3 years after insertion. No implants had been lost after 3 years and all prostheses were present and continuously functional. The morphotypic analysis of the microbial plaque taken from titanium implants adjacent to clinically inflamed tissues was different from that described of the dental plaque associated with sites of gingival inflammation. Radiographs demonstrated early horizontal bone loss adjacent to osseointegrated fixtures and occasional continuing horizontal bone loss at some sites during the 1st and 2nd years after prosthesis installation. All fixtures remained integrated after 3 years of function supporting fixed prostheses. Minor differences between the results of this study and earlier studies may reflect differences in surgical technique.

Mitogenic stimulation of human B lymphocytes by the mannose-specific adhesin on Escherichia coli type 1 fimbriae.

Escherichia coli type 1 fimbriae contain in association with the major structural protein a lectin-like adhesin moiety that mediates attachment of E. coli to mannose-containing receptors on the surface of host cells. We have investigated the lymphocyte mitogenic activity of this mannose-specific adhesin by comparing the ability of purified wild type type 1 fimbriae containing the adhesin and mutant type 1 fimbriae lacking the adhesin to stimulate proliferation in human lymphocytes. Both fimbriae stimulated a peak of proliferation at 8 days whereas only the wild type fimbriae stimulated an additional peak of proliferation occurring at 3 days. Proliferation at 3 days but not at 8 days could be blocked by the addition of alpha-methyl-D-mannoside. Neonatal lymphocytes from umbilical cord blood responded to both wild type and mutant fimbriae in a fashion similar to adult cells. Stimulation of separated T and non-T cell populations indicated that the proliferation seen at 3 days was solely due to non-T cells whereas the 8-day response was due to T cell proliferation. The addition of gamma-irradiated T cells did not appear to enhance the 3-day response of the non-T cells. However, the 8-day response by T cells was dependent on the presence of gamma-irradiated non-T cells. In cultures of unseparated cells, wild type fimbriae stimulated more than 75% of the B cells to enter the S and G2 phase at 3 days whereas at 8 days cycling T cells were present in both wild type and mutant fimbriae-stimulated cultures. Taken together, our observations suggest that the adhesin molecule stimulates a polyclonal mitogenic response in B cells that peaks at 3 days, and other structural components of the fimbriae are responsible for evoking an 8-day (probably immune) response in T cells.

The quantitative determination of hydrated calcium sulphates in cement by use of self-generating atmosphere thermogravimetry.

A method is described for the quantitative determination of hydrated calcium sulphates in cement by use of self-generating atmosphere thermogravimetry. The method is rapid and precise and can be applied (with a suitably modified sample container) with most thermogravimetric equipment.

A simple method for improving control of the time constant in recording transient signals in atomic-absorption spectrometry.

Significant improvements can be made in signal:noise ratios of transient signals arising in atomic-absorption spectroscopy by the use of resistor-capacitor damping. A suitable device is described and the effect it has on signals arising from instruments using analogue and digital forms of output is demonstrated.

Rapid analysis of small glass fragments by atomic-absorption spectroscopy.

A rapid method is described for the determination of magnesium, iron and manganese in small glass fragments (250-500 mug). The speed of the analytical procedure is made possible by the use of a convenient cold digestion stage allied to a discrete sampling method which permits the three elements of interest to be determined by flame atomic-absorption spectrophotometry.

Sensitivity enhancement in flameless atomization systems by use of a rigid tungsten collar.

Sensitivity enhancement was achieved in a flameless atomization system by the insertion of a rigid tungsten "collar" 1 cm long and 0.5 mm thick. With such a collar the electrical and thermal properties of the furnace were essentially those of the original tube, and the existing power pack could be used without modification. A significant improvement in sensitivity was found for the majority of the sixteen elements studied. The system did not appear to suffer from the deformation problems associated with other systems of atomization from metal surfaces.

The determination of thallium in urine by atomic absorption spectroscopy and emission spectrography.

The detection and measurement of thallium in urine samples using atomic absorption spectroscopy and emission spectrography is described. The sensitivity and precision of the methods are shown to be adequate for rapid routine screening in cases of suspected thallotoxicosis.