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Biomedical subjects

J Freedman

Publications and source records attributed to J Freedman.

At least 73 records · Page 4Linked to original sources
PubMed1998

Intravenous immunoglobulin and anti-D in idiopathic thrombocytopenic purpura (ITP): mechanisms of action.

Infusion of large amounts of intravenous immunoglobulin (IVIG) or anti-D can reverse the low platelet count in patients with ITP within hours of the initiation of treatment. In some cases, the effects of IVIG appear to far outlast several half-lives of the product. Several mechanisms have been proposed to explain these rapid and long term effects and these will be discussed in this review.

Antibodies, Anti-Idiotypic↗
PubMed1998

The Platelet Function Analyzer (PFA-100): a novel in-vitro system for evaluation of primary haemostasis in children.

The PFA-100 system provides an in-vitro method of assessing primary platelet-related haemostasis by measuring the time (the closure time, or CT) taken for a platelet plug to occlude a microscopic aperture cut into a membrane coated with collagen and either epinephrine or ADP. We used the system to establish normal ranges for CTs in healthy children, adults and neonates. Mean CTs of healthy children were independent of the needle gauge used (21G or 23CG) for blood sampling; they were very similar to the mean CTs of healthy adults, but longer than mean CTs of healthy neonates. Although children with haemophilia had normal CTs, the PFA-100 system was found to be potentially useful in screening for von Willebrand disease in children.

Adolescent↗
PubMed1998

Characterization of HIV-1-specific antibodies and HIV-1-crossreactive antibodies to platelets in HIV-1-infected haemophiliac patients.

Sera from HIV-1-infected haemophiliacs were examined for human immunodeficiency virus (HIV) specific antibodies and for platelet crossreactive antibodies. Using HIV sepharose 4B affinity columns for serum absorption, antibodies against various HIV antigens, including HIV lysate. HIV-p24 and HIV-gp120, were eluted either by low or by high pH buffer. The eluates were examined by ELISA for HIV specificity and by flow cytometry for platelet crossreactivity. Two types of HIV antibodies could be eluted, i.e. acid-sensitive and alkaline-sensitive antibodies. HIV antibodies were obtained in 26/29 acid eluates and in 25/29 of the alkaline eluates from HIV-lysate columns; 96% (25/26) of the acid-eluted antibodies were HIV-specific but 48% (12/ 25) of the alkaline-eluted antibodies also showed crossreactivity to platelets. Of the 20 alkaline-eluted HIV-p24 antibodies, 40% (8/20) reacted specifically with HIV-p24 and 60% (12/20) were platelet crossreactive. In contrast, of the alkaline-eluted HIV-gp120 antibodies (n=17), 88% (15/17) were HIV gp120-specific and only 12% (2/17) were platelet crossreactive. Western blot analysis of platelets demonstrated that the anti-p24 antibodies recognized three bands with approximate molecular weights of 72000 to 95000. 69% of the serum antiplatelet antibodies showed platelet glycoprotein IIbIIIa specificity. Anti-HIV antibodies could be eluted from platelets. Hence, platelet crossreactive antibodies in HIV infection are primarily alkaline-sensitive and are associated predominantly with HIV p24 antibody; these antibodies may play a role in the immune thrombocytopenia of HIV-infected haemophiliacs.

Acquired Immunodeficiency Syndrome↗
PubMed1998

Idiopathic thrombocytopenic purpura (ITP): a historical odyssey.

Purpura has been recognized since ancient times and its clinical syndromes were refined by important observations in the sixteenth, seventeenth and eighteenth centuries. It required the development of adequate microscopes in the nineteenth century, however, to recognize the platelet, leading to the recognition of the thrombocytopenic component of ITP. The twentieth century brought recognition of the pathophysiology of the disorder and further defined the clinical states and treatments for ITP. The latter half of the twentieth century has focussed on the autoimmune components of ITP, initially on the humoral immune aspects and more recently on dysregulation of cellular immunity.

History, 16th Century↗
PubMed1998

Reticulated platelet counts in the assessment of thrombocytopenic disorders.

Reticulated platelets (RP) are the youngest platelets in the circulation and can be measured by analysing the RNA content of platelets from whole blood or platelet-rich plasma by flow cytometry. Increased RP are indicative of increased production of platelets. Despite the current lack of standardization for the measurement of RP, it is useful in the assessment of patients with ITP by aiding the distinction of these patients from those with decreased platelet production. RP counts also have a role in the assessment of the complicated patient with multiple possible aetiologies for thrombocytopenia. Measurement of the RP count may hold predictive value for marrow recovery following myelosuppressive or myeloablative chemotherapy, and may play a role in monitoring the administration of the various thrombopoietins currently under clinical trial.

Blood Platelets↗
PubMed1998

Directions for research in autoimmune thrombocytopenic purpura (ITP).

All attendees participated in a round-table discussion regarding directions for research in autoimmune thrombocytopenic purpura (ITP). Suggested areas for study were grouped into five main areas: (i) improved classification of ITP identifying subsets of patients with differing clinical syndromes and response to treatment, and those more likely to have serious bleeding manifestations; identification of patients with reduced thrombopoiesis was emphasized; (ii) studies aimed at elucidating the aetiology and pathophysiology of ITP, with emphasis on distinctions between acute and chronic ITP and between patients responsive or refractory to therapy; these studies focused on measures of humoral and cellular immune dysregulation; (iii) studies of platelet function in ITP, with the intent of defining these abnormalities and correlating them with the clinical manifestations of the disease; (iv) new approaches to treatment, particularly of refractory patients; and (v) a miscellaneous group, which included development of an ITP registry, evaluation of the "burden" of disease, investigation of mood changes in ITP, etc. The discussion was not intended to be all-inclusive, but focused on the content of other talks in this symposium. It is hoped that some of these suggestions will be further developed for investigation in multicentre co-operative studies to improve the diagnosis, understanding and treatment of ITP.

Humans↗
PubMed1998

Management of chronic immune thrombocytopenic purpura in children and adults.

Chronic immune thrombocytopenic purpura (ITP) is characterized by macrophage destruction of platelets, primarily in the spleen, and occurs in both adults and children. Historically, splenectomy is often required, especially in adults with chronic ITP; however, several medical options have been used successfully prior to splenectomy or when this procedure has either failed or been refused by the patient. These include corticosteroids, intravenous immunoglobulin (IVIg), intravenous anti-D, danazol, vinca alkaloids, and other immunosuppressive agents such as azathioprine and cyclophosphamide. Platelet transfusions have been used in emergency situations. Several therapies that have been reported, but that are rarely used in chronic ITP, include cyclosporine A, interferon-alpha (IFN-alpha), plasma exchange, staphylococcal protein A immunoadsorption, combination chemotherapy, dapsone, ascorbic acid, and colchicine. Each of these approaches to treatment of chronic ITP are discussed.

Adrenal Cortex Hormones↗
PubMed1998

Management of the Molteno silicone tube in corneal transplant surgery.

A method to prevent tube-corneal touch in patients with Molteno implants who require corneal transplants is presented. A double-armed 10-0 Prolene suture is passed from limbus to limbus so that within the anterior chamber the suture acts as a splint for the silicone tube of the Molteno implant, keeping it away from the cornea. This suture has been used in six patients, all aphakic or pseudophakic, requiring corneal transplants for bullous keratopathy. In all six patients, the silicone tube was successfully splinted away from the endothelium of the corneal transplant.

Anterior Chamber↗
PubMed1998

Delivering labeled teaching images over the Web.

The Web provides educators with the best opportunity to date for distributing teaching images across the educational enterprise and within the clinical environment. Experience in the pre-Web era showed that labels and information linked to parts of the image are crucial to student learning. Standard Web technology does not enable the delivery of labeled images. We have developed an environment called OverLayer that succeeds in the authoring and delivering of such images in a variety of formats. OverLayer has a number of functional specifications, based on the literature and on our experience, among them, the following: Users should be able to find components by name or by image; to receive feedback about their choice to test themselves. The image should be of arbitrary size; should be reusable; should be linked to further information; should be stand-alone files. The labels should not obscure the image; should be linked to further information. Images should be stand-alone files that can be transferred among faculty members. Implemented in Java, OverLayer (http:/(/)omie.med.jhmi.edu/overlayer) has at its heart a set of object classes that have been reused in a number of applets for different teaching purposes and a file format for creating OverLayer images. We have created a 350-image histology library and a 500-image pathology library, and are working on a 400-image GI endoscopy library. We hope that the OverLayer suite of classes and implementations will help to further the gains made by previous image-based hyperlinked technologies.

Anatomy↗
PubMed1997

Binding of thrombin to the G-protein-linked receptor, and not to glycoprotein Ib, precedes thrombin-mediated platelet activation.

The roles of the G-protein-linked thrombin receptor and platelet glycoprotein Ib (GPIb) as alpha-thrombin-binding sites on platelets remain controversial. alpha-Thrombin has been proposed to bind to both GPIb and the hirudin-like domain of the G-protein-linked receptor (from which it cleaves the NH2-terminal extracellular domain to release a 41-mer peptide (TR-(1-41), where TR is alpha-thrombin receptor)) to initiate platelet activation. Using affinity-purified rabbit anti-human TR-(1-41) IgG and immunoblotting, we demonstrated TR-(1-41) release from platelets suspended in Tyrode's buffer containing 2 mM CaCl2 and incubated with >/=0.5 nM alpha-thrombin for 10-60 s at 37 degrees C. As quantified by enzyme-linked immunosorbent assay, 0.32-0.59 nM TR-(1-41) was released from washed platelets (5 x 10(11) platelets/liter) after their incubation with 10 nM alpha-thrombin for 10 s. Parallel binding of alpha-thrombin to and activation of the platelets were confirmed by flow cytometry. A monoclonal antibody against the hirudin-like domain of the G-protein-linked receptor abrogated alpha-thrombin binding to platelets, cleavage of TR-(1-41), and platelet activation by </=1.0 nM (but not 10 nM) alpha-thrombin. Proteolysis of platelet GPIb with Serratia marcescens protease or O-sialoglycoprotein endopeptidase had no effect on alpha-thrombin binding to platelets or their subsequent activation. In contrast, chymotrypsin, which cleaves both GPIb and the G-protein-linked receptor, abrogated alpha-thrombin binding to platelets, TR-(1-41) release, and platelet activation. Furthermore, monoclonal antibodies directed against the reported alpha-thrombin-binding site on GPIb inhibited neither alpha-thrombin binding to nor activation of the platelets. Thus, alpha-thrombin binds to and cleaves the G-protein-linked receptor when it activates platelets, and GPIb does not appear to serve as an important binding site when alpha-thrombin activates platelets.

Antibodies, Monoclonal↗
PubMed1997

Pentastarch instead of albumin as replacement fluid for therapeutic plasma exchange. The Canadian Apheresis Group.

BACKGROUND: Human albumin is commonly used as a replacement fluid in therapeutic plasma exchange (PE). In order to determine whether Pentaspan (PES), a synthetic low molecular weight starch solution, might be an effective substitute, we compared albumin with PES in 12 patients with myasthenia gravis or Guillain-Barré syndrome. STUDY DESIGN AND METHODS: Six patients were randomly assigned to receive PES and six to receive albumin as replacement fluid during their course of PE, which consisted of two to five treatments delivered over a maximum of 10 days. All patients were hospitalized and observed closely. Blood pressures were recorded every 4 hours and daily measurements were made of hematologic, coagulation, and immunoglobulin parameters. RESULTS: Individual exchange volumes were similar in each group (37 ml/kg--range 6-62--in patients receiving albumin vs. 41 ml/kg--range 6-41--in those receiving PES). Changes in immunoglobulin levels and coagulation parameters were similar but mild, transient thrombocytopenia was observed in three subjects given PES. Total serum protein and albumin levels decreased significantly in patients replaced with PES. Clinically, PES was well tolerated. Hypotension occurred in one patient who developed septic shock due to an infected femoral catheter; in another patient, a pre-existing pleural effusion was thought to increase slightly. CONCLUSIONS: PES appears to be a safe replacement fluid for PE, but larger clinical studies are required to confirm these findings.

Adult↗
PubMed1997

The effect of exercise on lymphocyte redistribution and leucocyte function in asymptomatic HIV-infected subjects.

This study was undertaken to examine the responsiveness of circulating leucocyte and lymphocyte populations to the physiological demands of exercise in asymptomatic HIV-infected subjects with CD4+ counts greater than 500/microliter. Thirteen subjects infected with HIV and 14 control subjects underwent 20 min of defined moderate exercise at estimated 65% of their maximal ventilatory capacity on a bicycle ergometer. Blood samples were obtained for serum cortisol, norepinephrine, lymphocyte subsets (CD4, CD8, CD19, CD16-CD56), and phagocytic function at rest immediately after exercise and 20 min following the cessation of the exercise. The HIV-infected subjects had increased circulating concentrations of CD8 cells (p = .007) and CD16-CD56+ NK cells (p = .02) in response to the exercise, whereas the control group did not. There was a greater increase in monocyte respiratory burst activity following recovery from exercise in the control subjects (p = .016) but not in the HIV-infected subjects. The control subjects experienced an increase in serum cortisol in response to the exercise (p = .006), but the HIV-infected subjects did not. Our results show that the changes in the distribution and function of circulating leucocytes and adrenal neuroendocrine responses to moderate exercise differ in asymptomatic HIV-infected and control subjects.

Adult↗
PubMed1997

Platelet and immune responses to oral cyclic dexamethasone therapy in childhood chronic immune thrombocytopenic purpura.

OBJECTIVE: To examine the effectiveness of cyclic oral high-dose (HD) dexamethasone therapy in pediatric patients with chronic immune thrombocytopenic purpura (ITP), which has been reported to cause complete remission in adults with chronic ITP. STUDY DESIGN: Eleven children with primary chronic ITP, with a median disease duration of 28 months (range, 6 to 120 months), were treated with cycles of HD dexamethasone therapy. RESULTS: Excellent short-term responses (initial platelet counts < or = 50 x 10(9)/L, increasing to > 100 x 10(9)/L within 72 hours of completion of an HD dexamethasone cycle) were observed in 78% of 41 cycles. Long-term effects include one complete response (platelet count > or = 150 x 10(9)/L) and three partial responses (platelet count > or = 50 and < 150 x 10(9)/L) in 11 children followed for 6 or more months after completing cyclic HD dexamethasone therapy. Because side effects were substantial, three children did not complete their sixth treatment cycle. At day 6 of treatment, B lymphocytes were significantly increased (p = 0.005). CONCLUSIONS: Dexamethasone, given orally in high doses, is an effective drug in achieving short-term platelet responses, but it induced long-term remissions in fewer than half of the children with well-established chronic ITP. Its effect on B lymphocytes requires further elucidation. A prospective, controlled study will be needed to establish whether cyclic HD dexamethasone therapy can alter the natural history of children with early chronic ITP and thus avoid splenectomy.

Administration, Oral↗
PubMed1997

Flow cytometric analysis of platelets from children with the Wiskott-Aldrich syndrome reveals defects in platelet development, activation and structure.

The pathophysiology of platelet dysfunction in the Wiskott-Aldrich immune deficiency syndrome (WAS) remains unclear. Using flow cytometry, we have characterized the functional properties of platelets from 10 children with WAS. Patients with WAS had thrombocytopenia, small platelets, increased platelet-associated IgG and reduced platelet-dense granule content. Levels of reticulated 'young' platelets were normal in the WAS patients. Although the mean numbers of platelet glycoprotein (GP) Ib, GPIIbIIIa and GPIV molecules per platelet appeared lower in WAS patients than in healthy controls, analysis of similar-sized platelets revealed the mean number of GPIb molecules per platelet to be comparable in patients and normal controls. Surface GPIIbIIIa and GPIV expression was, however, significantly lower on the WAS platelets than on normal platelets. Compared with normal platelets, WAS platelets showed a reduced ability to modulate GPIIbIIIa expression following thrombin stimulation. In addition, thrombin- and ADP-induced expression of CD62P and CD63 was defective in WAS platelets. Phallacidin staining of the WAS platelets revealed less F-actin content than in normal platelets. Together, these data suggest that the reduced platelet number and function in WAS reflects, at least in part, a defect in bone marrow production as well as an intrinsic platelet abnormality.

Actins↗
PubMed1997

Bronchiolitis obliterans with organizing pneumonia and cold agglutinin disease associated with phenytoin hypersensitivity syndrome.

Phenytoin hypersensitivity syndrome (PHS) is a rare delayed hypersensitivity reaction which occurs following exposure to phenytoin sodium. Pulmonary involvement is uncommonly described. Herein is reported the first case of histopathologic bronchiolitis obliterans organizing pneumonia (BOOP) found on open-lung biopsy in a patient with severe PHS. New onset, clinically significant, cold agglutinin disease was also documented. Hemodynamic parameters mimicking sepsis were present in the absence of significant clinical infection. Rapid, dramatic improvement followed high-dose steroid therapy.

Adult↗
PubMed1996

Recipient humoral immunity against leukoreduced allogeneic platelets is suppressed by aminoguanidine, a selective inhibitor of inducible nitric oxide synthase.

Leukoreduced allogeneic platelet transfusions have been previously shown to initially stimulate an in vitro cellular cytotoxicity and subsequently Induce the formation of immunoglobulin G (IgG) antidonor alloantibodies. To further characterize these responses and determine if they are related, recipient BALB/c H-2d mice were treated with aminoguanidine (AMG), a selective inhibitor of inducible nitric oxide synthase (iNOS), and transfused weekly with 2 x 10(8) C57BL/6 H2b platelets. In control, non-AMG-treated mice, transfusion significantly (P < .01) increased serum levels of interferon-gamma (IFN-gamma) by day 1 posttransfusion (PT). IFN-gamma returned to pretransfusion levels by day 3 PT, and its production was not affected by AMG treatment. Serum interleukin-4 (IL-4), on the other hand, was undetectable before and during the transfusion protocol. By day 3 PT, recipient spleen cells could mediate in vitro anti-P815 (auto), anti-EL4 (allo), and anti-R1.1 (third-party MHC) cytotoxicity, and these responses were maximal by day 7 PT. Concurrently, a significant reduction in the vitro ability of recipient splenocytes to respond to Concanavalin A (ConA) was observed; this was not seen with lipopolysaccharide (LPS) stimulation. Elevated levels of NO2- were found in the ConA culture supernatants from transfused mice at day 3 PT. Serum antidonor alloantibodies were detected by the fifth platelet transfusion. AMG treatment of recipient mice significantly inhibited the transfusion. Induced cytotoxicity and ConA-stimulated NO2- production, and restored ConA-induced proliferation to normal levels. AMG appeared to selectively inhibit platelet-induced alloantibody production in that it did not affect antibody production induced by transfusions with 10(5) allogeneic leukocytes or by immunization with a foreign protein antigen, human gamma globulin, in adjuvant therapy. These results indicate that an in vivo AMG-sensitive mechanism is essential for recipients to initiate a humoral IgG immune response against allogeneic platelets.

Animals↗