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Biomedical subjects

R H Aster

Publications and source records attributed to R H Aster.

At least 37 records · Page 2Linked to original sources
PubMed1999

Minimal evidence of platelet and endothelial cell reactive antibodies in thrombotic thrombocytopenic purpura.

Thrombotic thrombocytopenic purpura (TTP) is a syndrome characterized by microvascular thrombosis with thrombocytopenia and end-organ injury. Evidence suggests that platelet or endothelial cell injury may be initial pathological events in TTP. A number of factors in patient plasma, including immunoglobulins, have been proposed to mediate cellular injury in TTP. However, systematic analyses of TTP patient plasma for the presence of platelet or endothelial cell antibodies are lacking. We, therefore, analyzed 48 TTP patient plasma samples for the presence of platelet and endothelial cell antibodies by using enzyme-linked immunosorbent assay, flow cytometry, and microlymphocytotoxicity. Twelve of 48 TTP patient samples (25%) reacted against purified platelet glycoproteins. Nine (19%) also contained antibodies that bound to allogeneic target platelets in flow-cytometric assays. Nine of 48 samples (19%) contained antibodies to human umbilical vein endothelial cells in flow-cytometric assays, and seven of 48 patient samples (15%) bound to human dermal microvascular endothelial cells. Six of 48 (13%) patient plasma samples contained antibodies that bound to human umbilical vein endothelial cells activated with gamma-interferon and tumor necrosis factor-alpha. Of twenty samples that were reactive in one or more platelet or endothelial cell assay, eight contained human leukocyte antigen antibodies reactive in microlymphocytotoxicity. These studies demonstrate that antibodies reactive against platelet or endothelial cell antigens are not prevalent in TTP, and that more than a third of antibodies detected are human leukocyte antigen alloantibodies. Our findings suggest that autoantibodies against platelets or endothelial cells are not important in the pathogenesis of this syndrome.

Autoantibodies↗
PubMed1999

Drug-induced immune thrombocytopenia: an overview of pathogenesis.

Many drugs are capable of causing antibody-mediated thrombocytopenia. Four, and perhaps five, different mechanisms have been implicated in the pathogenesis of this family of disorders. Some drugs become bound covalently to platelet membrane glycoproteins in vivo and stimulate the production of hapten-dependent antibodies that recognize drug-membrane protein targets. Others, such as quinidine, quinine, and sulfonamide antibiotics, induce the formation of an unusual class of antibodies that bind to membrane glycoproteins only when the drug (or one of its metabolites) is present in solution. Certain drugs trigger the production of true autoantibodies capable of binding to cell membrane glycoproteins in the absence of drug. Heparin-induced immune thrombocytopenia (HIT) is associated with antibodies specific for complexes formed between heparin and platelet factor 4 (PF4), a basic protein of the chemokine family found normally in platelet alpha granules. Immune complexes consisting of heparin, PF4, and antibodies are important in the pathogenesis of HIT, but the exact mechanisms by which they cause platelet destruction and, in some patients, thrombosis are not yet fully understood. Finally, thrombocytopenia in patients treated with recently introduced inhibitors of the platelet fibrinogen receptor (ligand mimetics) is thought to result from antibodies specific for ligand-induced binding sites (LIBS) on this receptor, but this mechanism has not yet been established.

Humans↗
PubMed1998

An antibody from a patient with ranitidine-induced thrombocytopenia recognizes a site on glycoprotein IX that is a favored target for drug-induced antibodies.

Although thrombocytopenia associated with the use of histamine H2 receptor (H2R) antagonists has been described, a drug-dependent, platelet-reactive antibody has not previously been identified in such cases. We studied serum from a patient who developed acute, severe thrombocytopenia after exposure to the H2 receptor antagonist, ranitidine, and identified an antibody that reacted with normal platelets in the presence of this drug at pharmacologic concentrations. In flow cytometric and immunoprecipitation studies, the antibody was shown to be specific for the glycoprotein Ib/IX complex (GPIb/IX). From the pattern of monoclonal antibody (MoAb) inhibition and the reactions of antibody with Chinese hamster ovary (CHO) cells transfected with GPIX and GPIbbeta, we found that the patient's antibody is specific for an epitope on GPIX close to, or identical with a site recognized by the MoAb SZ1 that is a common target for antibodies induced by quinine and quinidine, drugs structurally unrelated to ranitidine. These findings provide evidence that immune thrombocytopenia can be caused by sensitivity to an H2 R antagonist and suggest that the SZ1 binding site on GPIX may be a common target for drug-induced antibodies. Further studies of the epitope for which SZ1 is specific may provide clues to the mechanism(s) by which drugs promote tight binding of antibody to a membrane glycoprotein and cause platelet destruction in patients with drug sensitivity.

Aged↗
PubMed1998

A recombinant soluble form of the integrin alpha IIb beta 3 (GPIIb-IIIa) assumes an active, ligand-binding conformation and is recognized by GPIIb-IIIa-specific monoclonal, allo-, auto-, and drug-dependent platelet antibodies.

The IIb-IIIa glycoprotein complex is a favored target for allo-, auto-, and drug-dependent antibodies associated with immune thrombocytopenia. A soluble, recombinant form of the GPIIb-IIIa heterodimer that could be produced in large quantities and maintained in solution without detergent could provide a useful experimental tool for the study of platelet-reactive antibodies, but previous attempts to produce such a construct have yielded only small quantities of the end product. Using a baculovirus expression system and the dual-promoter transfer vector P2Bac, we were able to express soluble GPIIb-IIIa complex (srGPIIb-IIIa) lacking cytoplasmic and transmembrane domains in quantities of about 1,000 microg/L, about 40 times greater than reported previously. The high yield achieved may be related to inclusion of the entire extracellular region of the GPIIb light chain in the construct. srGPIIb-IIIa reacts spontaneously with fibrinogen, and this interaction is totally inhibited by the peptide RGDS. Reactions of 24 GPIIb-IIIa-specific antibodies evaluated (12 monoclonal, 3 allo-specific, 3 auto-specific, and 6 drug-dependent) with srGPIIb-IIIa were indistinguishable from reactions with platelet GPIIb-IIIa. Thus, srGPIIb-IIIa spontaneously assumes an active, ligand-binding conformation and contains epitopes for all monoclonal and human antibodies tested to date. srGPIIb-IIIa can be produced in large quantities, can readily be modified by site-directed mutagenesis, and should facilitate identification of epitopes recognized by GPIIb-IIIa-specific antibodies, study of the mechanism(s) by which certain drugs promote antibody binding to GPIIb-IIIa in drug-induced thrombocytopenia and structure-function relationships of GPIIb-IIIa.

Antibodies, Monoclonal↗
PubMed1998

Antibodies from patients with heparin-induced thrombocytopenia/thrombosis recognize different epitopes on heparin: platelet factor 4.

Antibodies associated with heparin-induced thrombocytopenia/ thrombosis (HITT) are now thought to be specific for complexes formed between heparin and platelet factor 4 (PF4), a basic protein found normally in platelet alpha granules. How these antibodies cause thrombocytopenia and, in some patients, thrombosis, is not fully understood, in part because purified antibodies that could be labeled and used as probes to characterize target epitopes have not been available. We developed a novel method for antibody purification involving binding to and elution from PF4 complexed to heparin immobilized by end-linkage (EL) to a solid phase. Isolated antibodies were functional and after biotinylation, reacted with heparin: PF4 complexes in the same manner as unlabeled antibodies. Using these probes, we found that antibodies from 11 patients with HITT recognized two, and probably three, distinct sites on heparin: PF4 complexes. The antibodies did not bind to PF4 complexed with heparin immobilized by multiple chemical cross-linkages, suggesting that the heparin molecule must be in a flexible, relatively unconstrained state to react with PF4 in such a way as to create sites for HITT antibody binding.

Amino Acid Sequence↗
PubMed1998

Concurrence of anaphylaxis and acute heparin-induced thrombocytopenia in a patient with heparin-induced antibodies.

We report the occurrence of acute heparin-induced thrombocytopenia in a patient with anaphylaxis that began immediately after an intravenous bolus dose of unfractionated heparin. This case report is the first to document the concurrence of these 2 reactions to heparin. An abrupt fall in platelet count was documented immediately after the anaphylactic response. Study results for antibodies characteristic of heparin-induced thrombocytopenia were positive in 2 assays: serotonin release assay and heparin platelet factor 4 enzyme-linked immunosorbent assay. The patient's antibody was exclusively immunoglobulin G. Any explanation for the relationship between the antibody response observed and the histamine release remains speculative.

Acute Disease↗
PubMed1997

Sensitivity to a metabolite of diclofenac as a cause of acute immune hemolytic anemia.

A 75-year-old woman taking the nonsteroidal anti-inflammatory drug diclofenac (DCF) presented with acute Coombs-positive hemolytic anemia and subsequently developed renal failure. A drug-dependent antibody specific for red blood cells (RBCs) could not be demonstrated by in vitro testing with DCF. However, her serum was found to contain an IgM antibody that reacted strongly with RBCs in the presence of urine from any of four subjects who had ingested DCF. The active substance in urine was isolated, subjected to high-performance liquid chromatographic (HPLC) analysis, and found to be a glucuronide conjugate of a known DCF metabolite, 4'-hydroxydiclofenac (4'-OH DCF). Negative results were obtained with four other DCF metabolites. Two 4'-OH DCF glucuronides were synthesized in vitro using a liver microsomal system. One promoted agglutination of normal RBCs by the patient's serum and was identified as the glucuronide ester of 4'-OH DCF by proton nuclear magnetic resonance (NMR) analysis. Studies with a panel of RBCs showed that the patient's antibody reacted preferentially with the e antigen of the Rh system. Acute immune hemolytic anemia in this patient appears to have been caused by sensitization to DCF modified by 4' hydroxylation and glucuronidation. This is the first reported example of immune cytopenia caused by sensitivity to a glucuronide conjugate of a drug metabolite. Since glucuronidation is a common pathway of drug metabolism, studies of the frequency with which glucuronide derivatives of primary medications cause immune cytopenia seem warranted.

Aged↗
PubMed1997

Thrombotic thrombocytopenic purpura: early and late responders.

Thrombotic thrombocytopenic purpura (TTP) is characterized by micro-angiopathic hemolytic anemia (MAHA), thrombocytopenia, neurological symptoms, renal involvement, and fever. We describe our experience in 70 serially encountered TTP patients in the last decade who were treated with a standard therapeutic plasma exchange (TPE) protocol. Seventy percent of the patients were females. The median age of the patients was 43 years (range: 8-80). Sixty patients (85.7%) had a complete response to TPE therapy. This represented 91% of 66 who received at least one TPE. Ten patients died, two patients died before and two during the first plasma exchange. The median number of TPEs performed was nine (range: 1-85). Thirty-five (58%) out of 60 responded to 3-9 TPEs, and 25 (42%) required 10-34 TPEs for the response. The median total plasma volume exchanged was 28 liters (range: 2.7-250 L) and the mean plasma volumes exchanged during each procedure was 3.2 (SD +/- 1.09 L). The patients were classified into early responders (ER) and late responders (LR). ERs had a mean platelet count of 180 x 10(9)/L by Day 5, mean LDH of 643 IU/L by Day 7, and required median of seven TPEs. LRs had a mean platelet count of 122 x 10(9)/L by Day 5, mean LDH of 885 IU/L by Day 7, and required median of 19 TPEs (P = 0.001). The platelet counts were significantly higher (P = 0.01-0.03) in ERs on Days 1, 3, and 5 as compared to LRs but the LDH did not differ significantly. Seventy-seven percent of LRs had exacerbation of TTP and 18% had relapse as compared to 7% each in ERs. Thirteen patients were in coma/semicoma at presentation. Out of these, six died, making coma a bad prognostic indicator. Five of the seven survivors in coma had received two single-plasma volume exchanges on Day 1. In conclusion, 91% of TTP patients had an excellent response to plasma exchange therapy with FFR Coma/ semicoma appears to be a bad prognostic indicator. LRs needed prolonged treatment with a greater number of patients experiencing exacerbation and relapse of TTP as compared to ERs.

Adolescent↗
PubMed1997

Characterization of the humoral immune response in heparin-induced thrombocytopenia.

Recent reports indicate that antibodies associated with heparin-induced thrombocytopenia and thrombosis (HITP) are specific for complexes formed between heparin and the heparin-binding, platelet alpha granule protein, platelet factor 4 (PF4). As with other disorders mediated by immune complexes (IC), the characteristics of the involved immunoglobulins could affect the ability of IC to cause symptoms. We therefore studied the class, subclass, and potency of antibodies specific for heparin:PF4 complexes formed by two groups of patients: one with severe thrombocytopenia, with or without thrombosis, and a positive serotonin release assay (SRA) (Group 1) and another with mild or absent thrombocytopenia, absence of thrombosis, and a negative SRA despite having formed antibodies reactive with heparin:PF4 complexes (Group 2). IgG antibodies were more common in the Group 1 patients (100%) than in Group 2 (46%), whereas IgM antibodies were more common in Group 2 (81%) than in Group 1 (42%) (P = 0.009). About half of each group formed IgA antibodies. In each group, the IgG antibodies were predominantly IgG1 (82%); 42% were IgG3. Only one IgG2 antibody was identified in a total of 52 antibody formers. Antibodies of the IgG class were consistently of higher titer in Group 1 patients than in Group 2 patients (P < 0.001). Recent reports suggest that the H131 form of the Fc gammaRII receptor, which binds preferentially to IgG2 Fc, is found with greater than expected frequency in patients with HITP. Identification of only one IgG2 antibody among 38 antibodies of the IgG class argues against a unique role for antibodies of this subclass in the pathogenesis of HITP. The finding that titers of antibodies in Group 1 patients were a significantly higher titer than in Group 2 patients suggests that development of the full-blown HITP syndrome may require the formation of antibodies of unusually high titer.

Aged↗
PubMed1996

Patients treated with unfractionated heparin during open heart surgery are at high risk to form antibodies reactive with heparin:platelet factor 4 complexes.

Recent studies have demonstrated a strong association between type II (immunologically mediated) heparin-induced thrombocytopenia/thrombosis (HITP) and antibodies reactive with complexes consisting of heparin and platelet factor 4 (PF4), a heparin-binding protein normally found in platelet-alpha granules. However, the frequency with which such antibodies develop in patients given treatment with heparin has not yet been defined. We studied the development of heparin:PF4-specific antibodies in 51 patients who received a single dose of unfractionated heparin (UFH) during cardiac catheterization and were then given UFH or low-molecular-weight heparin (LMWH) again during and after open heart surgery. Eleven of the 51 patients (22%) had antibodies reactive with heparin:PF4 when they were admitted for cardiac surgery; these antibodies were mainly of the immunoglobulin M (IgM) class and were apparently stimulated by exposure to UFH at cardiac catheterization. Seventeen of 34 patients (50%) without preexisting antibody who were given UFH during and for 1 to 3 days after surgery formed immunoglobulin G antibodies or IgM antibodies (or both) by the sixth postoperative day. Overall, 27 of 44 patients (61%) who were given UFH at surgery had antibodies by the time of hospital discharge. None of 6 patients without preexisting antibody who were given LMWH at surgery formed antibodies (p < 0.03). However, LMWH was given as a single injection only on the day of surgery. The titer of the antibodies formed by patients receiving UFH ranged from 1:10 to 1:200, significantly lower than those in patients with a clinical diagnosis of HITP. Moderate thrombocytopenia was common after open heart surgery, but platelet levels in patients who had preexisting antibodies or formed new antibodies did not differ significantly from those in patients without antibody. Clinically significant thrombosis did not develop in any patient and HITP was not diagnosed in any patient. Antibodies reactive with heparin:PF4 formed in only 3 of 66 patients (4.5%) undergoing other types of surgery. One of these patients had been given UFH 3 months previously; the other 2 may have been exposed to heparin used to flush intravenous lines postoperatively. No antibodies reactive with heparin:PF4 were found in any of 108 normal subjects. We conclude that UFH is more immunogenic than has been thought and that patients exposed to this anticoagulant during open heart surgery are at high risk to form low titer (</= 1:200) antibodies reactive with heparin:PF4. Further studies are needed to determine whether such antibodies are clinically significant--that is, whether sensitized patients are at risk to develop HITP if heparin treatment is continued for more than 1 to 3 days or is reinstituted at a later date.

Adult↗
PubMed1996

Inhibition of platelet adhesion to collagen by monoclonal anti-CD36 antibodies.

Monoclonal anti CD36 antibodies capable of inhibiting platelet adhesion to collagen have not previously been identified. We have now prepared two groups of monoclonal antibodies. One group was prepared using, as immunogen, highly purified (99+%) CD36 prepared by a denaturing procedure. These antibodies (Mo series) reacted strongly with CD36 on protein blots but did not immunoprecipitate native CD36 from platelet lysates nor inhibit platelet adhesion to collagen. The second group of monoclonal antibodies (131 series) was prepared using CD36 purified to >95% by a non-denaturing procedure. These antibodies reacted with control platelets, but not Nak(a)-negative platelets which lack CD36, as measured by flow cytometry and immunoprecipitation. Three monoclonal antibodies of this latter group (131.4, 131.5 and 131.7) inhibited platelet adhesion to collagen in static systems under Mg2+ -independent conditions but had lit tle effect in the presence of Mg2+. 131.4 and 131.7 also inhibited adhesion to collagen using citrated whole blood in a parallel plate flow chamber at physiological shear rates (800s-1), whereas 131.5 was without effect. These are the first anti-CD36 monoclonal antibodies shown to be capable of inhibiting platelet adhesion to collagen and provide further evidence that CD36 plays a role in platelet-collagen interaction.

Animals↗
PubMed1996

Determination of neutrophil antigen gene frequencies in five ethnic groups by polymerase chain reaction with sequence-specific primers.

BACKGROUND: The granulocyte antigens NA1 and NA2 are the two recognized allelic forms of Fc gamma receptor IIIB. These antigens are clinically relevant, because they are the most frequent targets of neutrophil antibodies in alloimmune neonatal neutropenia, transfusion-related acute lung injury, and chronic benign autoimmune neutropenia of infancy. STUDY DESIGN AND METHODS: A genotyping assay for NA1 and NA2 using polymerase chain reaction with sequence-specific forward and reverse oligonucleotide primers has been developed and validated. Genomic DNA was isolated from the peripheral blood of 478 unrelated individuals of five ethnic groups and used as template for NA genotyping. RESULTS: A validation study of 22 serologically typed samples (2 NA1/NA1, 10 NA1/NA2, and 10 NA2/NA2) was performed. A concordance rate of 100 percent (22/22 samples) was observed between the genotyping assay and serologic typing. In the genotyping study conducted, the NA1 and NA2 gene frequencies observed were 0.31 and 0.69 for African Americans, 0.30 and 0.70 for Asian Indians, 0.37 and 0.63 for whites, 0.53 and 0.47 for Hispanics, and 0.55 and 0.45 for Native Americans, respectively. CONCLUSION: Polymerase chain reaction with sequence-specific primers provides a simple and rapid alternative to neutrophil antigen typing by serologic tests. The NA1 and NA2 gene frequencies observed in Asian Indians and African American populations are similar to those observed in white populations, while those observed in Native American and Hispanic populations are more similar to those previously reported for Asian populations.

Ethnicity↗