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Biomedical subjects

R R Montgomery

Publications and source records attributed to R R Montgomery.

At least 91 records · Page 5Linked to original sources
PubMed1985

Persistence and progression of immunologic abnormalities in haemophilia.

Immunologic parameters in 51 patients with haemophilia treated with cryoprecipitate from volunteer donors or with commercial lyophilized concentrate were studied on 2-7 occasions. Concentrate users had significantly decreased mean T4 (helper)/T8 (suppressor) lymphocyte ratios when the initial (1.5 +/- .43) and most recent (1.25 +/- .60) values were compared (p less than .001), whereas in cryoprecipitate users mean values remained normal. Of the 22 concentrate users with initially normal T4/T8 ratios, 10 became abnormal during the study, an incidence of 45%. Fifteen of 28 (54%) patients with abnormal T4/T8 ratios had elevated circulating immune complexes (CIC), whereas all 16 patients with normal T4/T8 ratios had normal levels of CIC. Six patients have persistent lymphadenopathy.

Antigens, Surface↗
PubMed1985

On the association of glycoprotein Ib and actin-binding protein in human platelets.

Glycoprotein (GP) Ib was purified from lysates of human platelets prepared in the presence or absence of inhibitors of the endogenous calcium-activated neutral protease (CANP) by immunoaffinity chromatography, employing the GPIb-specific murine monoclonal antibody, AP1, coupled to Sepharose CL4B. When derived from lysates prepared in the presence of EDTA or leupeptin, the eluate from the AP1-affinity column contained a 240,000-260,000-mol-wt protein in addition to GPIb. In SDS PAGE, this protein was stained by Coomassie Blue R, but not by the periodic acid-Schiff reagent, and it was not labeled with 125I in intact platelets by the lactoperoxidase-catalyzed method. When derived from lysates prepared in the absence of CANP inhibitors, the eluate contained only GPIb and its proteolytic derivative, glycocalicin. A change in the electrophoretic mobility of GPIb consistent with its association with the 240,000-260,000-mol-wt protein was confirmed by crossed immunoelectrophoresis. By an immunoblot technique involving transfer of proteins eluted from the AP1-affinity column and separated by SDS PAGE onto a nitrocellulose membrane, the 240,000-260,000-mol-wt protein bound polyclonal goat antibody raised against rabbit macrophage actin-binding protein (ABP). On the basis of these results, we conclude the GPIb is tightly associated with ABP under conditions in which the endogenous CANP is inhibited, and that this apparent transmembrane complex of GPIb-ABP can be isolated in lysates of nonactivated human platelets.

Actins↗
PubMed1985

Endothelial cell synthesis of von Willebrand antigen II, von Willebrand factor, and von Willebrand factor/von Willebrand antigen II complex.

von Willebrand antigen II (vW AgII) and von Willebrand factor (vWf) are immunochemically distinct proteins that are deficient in the plasma and platelets of patients with severe von Willebrand's disease. Normal human umbilical vein endothelial cells were cultured in the presence of [35S]methionine. Crossed immunoelectrophoresis of endothelial cell supernates and detergent-solubilized endothelial cells demonstrated specific incorporation of the [35S]methionine into vW AgII. Furthermore, when endothelial cells were lysed in the presence of proteolytic inhibitors, a second, less anodal peak was identified on crossed immunoelectrophoresis. This peak represented a complex of vW AgII and vWf and demonstrated a reaction of complete identity with the vW AgII immunoprecipitate. When plasma, serum, or platelets were evaluated by crossed immunoelectrophoresis, this "complex" peak was not present. When antibodies to vWf, fibronectin, or fibrinogen were present in the first dimension of crossed immunoelectrophoresis, only the antibodies to vWf removed the complex. Radioiodinated polyclonal and monoclonal antibodies to vWf also localized vWf to this complex. Under reducing conditions, sodium dodecyl sulfate-polyacrylamide gel electrophoresis of [35S]methionine-labeled immunoprecipitates indicated that the molecular weight of vW AgII is 98,000 and that vWf was present as two species of 220,000 and 260,000 mol wt, respectively. Immunofluorescent microscopy of endothelial cells demonstrated colocalization of vW AgII and vWf in endothelial cells with intense immunostaining of the same subcellular granules.

Antigens↗
PubMed1985

Cleavage of human von Willebrand factor by platelet calcium-activated protease.

In human platelet lysates prepared by addition of nonionic detergent (Triton X-100) or by sonication, the multimer composition and electrophoretic mobility of platelet von Willebrand factor (vWF) were consistently modified under conditions that would favor activation of the endogenous calcium-activated, sulfhydryl-dependent neutral protease (CAP). By sodium dodecylsulfate-agarose gel electrophoresis, native platelet vWF contained some multimers that were larger than those characteristic of plasma vWF. Modified platelet vWF contained a multimer population equivalent to or smaller than that of plasma vWF plus an additional fast-migrating band. In crossed immunoelectrophoresis (CIE), modified platelet vWF was characterized by a more anodic distribution and the appearance of a distinct, cross-reactive, anodic component previously designated VIIIR:Ag fragment. In the presence of calcium, radiolabeled purified plasma vWF was also degraded by the protease in question, with a decrease in the apparent molecular weight of the reduced monomer from 230,000 to 205,000. The VIIR:Ag fragment isolated from the same degraded plasma vWF by preparative CIE was shown to be composed of an identical mol wt 205,000 subunit. Because cleavage of plasma or platelet vWF was inhibited by prior addition of leupeptin, EDTA, ethylene glycol bis (beta-aminoethyl ether)-N, N, N', N'-tetraacetic acid (EGTA), or N-ethylmaleimide (agents known to inhibit platelet CAP) but was unaffected by numerous other protease inhibitors, including soybean trypsin inhibitor, benzamidine, hirudin, phenylmethylsulfonyl fluoride, aprotonin, or epsilon-aminocaproic acid (none of which inhibits platelet CAP), we conclude that proteolysis of vWF observed in this study is a direct effect of CAP and is not mediated by way of secondary proteases.

Blood Coagulation Factors↗
PubMed1985

Newborn haemostasis.

Although reliable haemostasis testing is difficult to obtain in the newborn infant, information gained from such testing is important to the diagnosis of hereditary and acquired haemostatic disorders. Newborn infants are at risk for developing haemorrhage or thrombosis when provoked by various pathological stimuli. Haemostasis screening tests and factor assays must be interpreted using gestational age-specific normal ranges. Frequently, the comparison of several factor assays provides the necessary information to diagnose and treat neonatal haemostatic abnormalities.

Blood Coagulation↗
PubMed1984

Severe homozygous protein C deficiency.

An infant with recurrent purpura fulminans in the first year of life was found to have severe homozygous deficiency of protein C (less than 1% of normal levels). The episodes of purpura fulminans were controlled by infusions of fresh frozen plasma containing protein C. The requirement of frequent plasma infusions, however, eventually resulted in several complications secondary to hyperproteinemia. Factor IX concentrates rich in protein C were then given to maintain adequate levels of the factor while minimizing the amount of extraneous proteins. The patient has remained asymptomatic and free of complications for greater than 10 months while receiving these concentrates every 48 hours.

Blood Coagulation Factors↗
PubMed1984

Comparison of the sensitivity of commercial APTT reagents in the detection of mild coagulopathies.

This study was undertaken to evaluate the precision and sensitivity of three different commercial APTT reagents containing the activators kaolin, micronized silica, or ellagic acid. These reagents varied greatly in their ability to detect mild coagulopathies. The ellagic acid reagent was able to detect the mildest deficiencies for the most common coagulopathies. This reagent was sensitive to 50% levels of Factor VIIIC, whereas the APTT with the kaolin reagent was not prolonged until levels of 35% or less were attained. The micronized silica reagent was the least sensitive to Factor IX deficiency, detecting levels of 12% or less. Precision was similar for all reagents when tested with normal and slightly abnormal plasmas. Since methods and instrumentation vary, each laboratory should evaluate their APTT reagent to determine its precision and sensitivity.

Blood Coagulation Disorders↗
PubMed1984

Interaction of von Willebrand factor with human platelets in the plasma milieu.

The binding of von Willebrand factor (vWf) to stimulated platelets in the plasma milieu was performed using a radiolabeled monoclonal antibody to vWf. Plasma proteins specifically inhibited the thrombin- and ADP/epinephrine-induced vWf binding to activated platelets but did not inhibit the ristocetin-induced vWf binding. When normal plasma was heat defibrinated, monoclonal-labeled vWf was bound to platelets following thrombin or ADP/epinephrine stimulation. Furthermore, monoclonal-labeled vWf from afibrinogenemic plasma bound normally to platelets. The binding of vWf to stimulated platelets in either heat-defibrinated normal plasma or afibrinogenemic plasma was specifically inhibited by the addition of normal plasma fibrinogen in a concentration-dependent manner. At levels of fibrinogen less than 1 mg/ml, however, vWf binding could be demonstrated. The inhibition by fibrinogen of vWf binding to platelets was competitive and overcome by increased concentrations of vWf. These studies show that thrombin-induced and ADP/epinephrine-induced vWf binding to platelets does not occur in the plasma milieu, although at reduced levels of fibrinogen, vWf binding to stimulated platelets can be demonstrated.

Adenosine Diphosphate↗
PubMed1984

Autoantibodies against platelet glycoprotein Ib in patients with chronic immune thrombocytopenic purpura.

The present studies provide direct evidence that some patients with chronic immune thrombocytopenic purpura (ITP) have autoantibodies reactive with platelet glycoprotein Ib ( GPIb ). Microtiter wells coated with a monoclonal antibody that recognized GPIb were reacted with either platelet extract or a control cell extract. After washing and incubating with test plasma, well-bound IgG was quantitated using radioactive anti-IgG. When compared to plasma from normal subjects, plasma from 3 of 106 patients with chronic ITP had significantly increased quantities of IgG bound to microtiter wells reacted with platelet extracts. Negative results were obtained with the remaining 103 patients with chronic ITP and 59 patients with a variety of other platelet disorders. Plasma from two of the three positive patients precipitated a protein from 125I-surface-labeled platelet extract with a molecular weight similar to GPlb . One of the three patients with anti- GPlb antibody also had demonstrable autoantibodies to the platelet glycoprotein llb / llla complex.

Acute Disease↗
PubMed1984

The effect of DDAVP on plasma levels of von Willebrand antigen II in normal individuals and patients with von Willebrand's disease.

The infusion of 1-deamino-(8-D-arginine)-vasopressin (DDAVP) causes not only an elevation in factor VIII-related antigen (FVIIIR:Ag), but also a marked elevation of plasma von Willebrand antigen II (vWAgII). vWAgII reaches a peak concentration at 60 min and is elevated 3-8-fold over basal levels in normal individuals and individuals with type I, IIA, and IIB von Willebrand's disease. As the mechanism of hemostatic alteration brought about by DDAVP might be due to release of endothelial cell proteins, endothelial cell cultures were performed. The cultures demonstrated synthesis and secretion of vWAgII, as evidenced by the incorporation of 35S-methionine into the vWAgII molecule. Thus, vWAgII, like FVIIIR:Ag, is an endothelial cell protein.

Antigens↗
PubMed1984

Correlation between circulating levels of von Willebrand's antigen II and von Willebrand factor: discrimination between type I and type II von Willebrand's disease.

Classification of the subtypes of von Willebrand's disease (vWd) has been based on a quantitative deficiency or an abnormal multimeric composition of von Willebrand factor (vWf). Although the co-deficiency of a second protein, von Willebrand's antigen II (vW AgII), had been previously recognized, its concentration in a relatively large number of normal individuals or patients with well-defined vWd variants had not been studied. The plasma from patients with type I, IIA, IIB, IIC, and III (severe) vWd was evaluated, and the concentrations of vW AgII and vWf were determined. Although patients with type I and III vWd had reduced levels of both proteins, the plasma vW AgII concentration was normal in patients with type II vWd. Analysis of the results indicates that type I and type II variants can be discriminated with greater than 80% accuracy by comparison of results of these two antigenic assays. The normal levels of vW AgII in type II variants suggest a possible difference in the pathophysiology of type I and type II vWd.

Antigens↗
PubMed1983

Interaction of AP-2, a monoclonal antibody specific for the human platelet glycoprotein IIb-IIIa complex, with intact platelets.

A murine monoclonal antibody, designated AP-2, reacts specifically with the complex formed by human platelet membrane glycoproteins IIb and IIIa, but does not react at all with the individual glycoproteins. Purified AP-2 covalently coupled to Sepharose CL4B was used as an immunoadsorbent column to purify the IIb-IIIa complex from a preparation of Triton X-100-solubilized human platelet proteins. Radioiodinated AP-2 was shown to bind to a single class of sites, with 57,400 +/- 9,700 molecules bound per cell (mean +/- S.D.) at saturation and a dissociation constant (Kd) of 0.64 +/- 0.15 nM (mean +/- S.D.). Binding could not be readily reversed even after a 1-h incubation with a 100-fold excess of cold antibody. AP-2 inhibits ADP-induced binding of radiolabeled fibrinogen to gel-filtered platelets in a noncompetitive fashion, consistent with the previous observation that AP-2 also inhibits the aggregation of platelets in plasma induced by a number of physiologic agonists, including adenosine diphosphate, epinephrine, collagen, thrombin, and arachidonic acid. Using AP-2, we have obtained evidence that the IIb-IIIa complex exists in the membrane of intact nonstimulated platelets and that complex integrity is not affected by external calcium ion concentration.

Antibodies, Monoclonal↗
PubMed1983

Regulation of mouse oocyte meiotic maturation: implication of a decrease in oocyte cAMP and protein dephosphorylation in commitment to resume meiosis.

Mouse oocytes are reversibly inhibited from resuming meiotic maturation in vitro by cAMP phosphodiesterase inhibitors such as 3-isobutyl-1-methyl xanthine (IBMX) and cAMP analogs such as dibutyryl cAMP (dbcAMP). Oocytes cultured in IBMX-containing medium were transferred to and cultured in IBMX-free medium for various periods of time prior to their return to either IBMX- or dbcAMP-containing medium. Results from these experiments defined a period of time in which oocytes became committed to resuming meiosis. Forskolin, which elevated the intracellular oocyte cAMP concentration, transiently inhibited oocytes from resuming meiosis. Levels of cAMP were determined in oocytes incubated in medium that allows resumption of meiosis. The level of oocyte cAMP decreased significantly during the time in which oocytes become committed to resuming meiosis. This decrease in oocyte cAMP was not observed in oocytes inhibited from resuming meiosis by IBMX. In addition, cAMP levels were determined in preovulatory antral follicles, cumulus cell-oocyte complexes, and oocytes during gonadotropin-induced resumption of meiosis in vivo. A decrease in oocyte cAMP preceded resumption of meiosis as manifested by germinal vesicle breakdown (GVBD). This decrease apparently occurred before or during a period of time in which follicle and cumulus cell cAMP were increasing. Associated with commitment to resume meiosis was a characteristic set of changes in oocyte phosphoprotein metabolism that preceded GVBD. These changes are, to date, some of the first reported biochemical changes that precede GVBD. Results from these experiments are discussed in terms of a possible role cAMP may play in regulation of resumption of meiosis in mammals.

1-Methyl-3-isobutylxanthine↗
PubMed1983

Generalized lymphadenopathy and T cell abnormalities in hemophilia A.

Two patients with hemophilia A had generalized lymphadenopathy, lymphopenia, elevated IgG values, depressed T4 (helper) lymphocytes, elevated T8 (suppressor) lymphocytes, and abnormally low T4/T8 ratios. One of the patients, who also had hepatosplenomegaly, underwent cervical lymph node biopsy; the node contained 43% T8-lymphocytes, a marked elevation over the small fraction of T8 cells usually found in lymph nodes. These patients may have a form of the acquired immune deficiency syndrome described in male homosexuals, Haitians, intravenous drug abusers, and recently, in patients with hemophilia. We studied T cell phenotypes in 43 patients with hemophilia. Fourteen of 28 patients given commercial factor VIII concentrates had abnormal T4/T8 ratios; none of nine patients who used cryoprecipitate had abnormal values. T4 helper cells were significantly lower, T8 suppressor cells significantly elevated, and T4/T8 ratios significantly lower in the lyophilized concentrate users and in patients with hemophilia as a total group. The type of therapeutic factor VIII replacement may alter the risk of developing T4/T8 abnormalities or AIDS.

Acquired Immunodeficiency Syndrome↗
PubMed1983

Diagnosis of Bernard-Soulier syndrome and Glanzmann's thrombasthenia with a monoclonal assay on whole blood.

Two hereditary platelet disorders, Bernard-Soulier syndrome and Glanzmann's thrombasthenia, are characterized by selective deficiencies of platelet membrane glycoproteins. Murine monoclonal antibodies were developed against platelet membrane glycoprotein Ib and against the glycoprotein IIb/IIIa complex. A rapid whole blood assay for the deficiency of these glycoproteins was developed and used to study whole blood samples from six patients with Glanzmann's thrombasthenia and three patients with Bernard-Soulier syndrome. Patients with type I and type II Glanzmann's thrombasthenia were easily detectable with this assay. This permits the diagnosis of these disorders on 200 microliters of whole blood within 2 h of blood sampling.

Animals↗