Clinical phenomena induced by complement and leukocyte interactions with artificial surfaces.
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Complement Activation↗
Biomedical subjects
A K Cheung
Publications and source records attributed to A K Cheung.
Macromolecule adsorption to hemodialysis membranes depends on molecular size.
Adsorption to hemodialysis membranes was studied by determining the binding kinetics of model macromolecules, polydisperse DEAE dextran (molecular radii 10-70 A), to an acrylonitrile-methallyl sulfonate copolymer membrane. Hemodialyzers were studied in a postdilution hemofiltration circuit where both blood path output and ultrafiltrate streams were returned to the reservoir. Changes in the reservoir concentration of and sieving coefficients for DEAE dextran were monitored over 24 h. Decreases (or increases) in reservoir concentration were assumed to result from adsorption to (or desorption from) the membrane. Small macromolecules adsorbed rapidly to the membrane but later desorbed. This rapid adsorption resulted in low initial sieving coefficients. Large macromolecules adsorbed slowly over the entire 24-hour study period. Additional experiments suggested that desorption of small macromolecules was due to displacement by large macromolecules. Adsorption and desorption of macromolecules to hemodialysis membranes are dynamic processes and depend on molecular size.
Acrylic Resins↗
Modulation of complement activation on hemodialysis membranes by immobilized heparin.
To determine the effects of surface-associated heparin on the capacity of hemodialysis membranes to activate complement, cellulose acetate (CA) membranes that were untreated and CA membranes that had been coated with heparin (HCA) were incubated with C3-depleted serum repleted with radio-labeled C3. Next, the proteins in the supernatant and those eluted from the membranes were subjected to sodium dodecyl sulfate-polyacrylamide gel electrophoresis. C3 activation was quantified by determining the radioactivity of the C3a-containing band in the gel. Total C3a generation (fluid phase C3a plus membrane-associated C3a) was three times greater in the presence of HCA compared with CA. Most (88%) of the C3a generated in the presence of HCA, however, was adsorbed onto the membrane surface. Consequently, there was more C3a in the CA supernatant than in the HCA supernatant. To determine the mechanism by which heparin enhanced alternative pathway activity, binding studies with radiolabeled factor B and factor H were performed. HCA bound 3.4 times more factor B and 20 times more factor H than did CA. The binding of these proteins, however, was not dependent on complement activation. Studies designed to test the functional activity of isolated factor H and factor B that had been adsorbed to the membrane showed that factor H was active on both CA and HCA, whereas factor B was active only on HCA. These data demonstrate that heparin immobilized onto CA hemodialysis membrane enhances C3 activation but produces low levels of C3a in the fluid phase because of high surface adsorption of the anaphylatoxin. Heparin appears to augment alternative pathway activity by favoring the interactions of factor B with other constituents of the amplification C3 convertase of the alternative pathway of complement.
Biocompatible Materials↗
Adherence of neutrophils to hemodialysis membranes: role of complement receptors.
Complement activation occurs during hemodialysis using cellulosic dialysis membranes with the consequent deposition of C3 activation and degradation products on the membrane surface. To determine if these complement fragments are functionally active, we examined their capacity to mediate leukocyte adherence to cuprophan membranes. Immunoblotting of proteins eluted from plasma-treated cuprophan membranes confirmed the presence of both C3b and iC3b. Incubation of cuprophan membranes with heparinized whole blood resulted in adherence of leukocytes but not erythrocytes. Neutrophils were the primary cell type bound, with monocytes comprising less than 5% of the adherent cells. Studies using indium-labeled neutrophils demonstrated that the binding was plasma dependent and increased with time up to two hours. Neutrophil binding was inhibited by preincubation of the plasma-treated cuprophan membrane with anti-C3 or preincubation of neutrophils with an antibody directed against the alpha chain of complement receptor type 3 (CR3). These observations indicate that iC3b deposited on cuprophan membrane surface as a result of complement activation mediates neutrophil adherence via interaction with CR3. They also support the hypothesis that, in addition to the anaphylatoxins released into the fluid phase, complement activation products that remained membrane bound during hemodialysis also stimulate pathophysiological responses.
Cell Adhesion↗
Cloning of the latency gene and the early protein 0 gene of pseudorabies virus.
A collection of overlapping cDNA clones encoding the latency transcript of pseudorabies virus and the DNA nucleotide sequence of the latency gene has been obtained. The transcript is spliced with 4.6 kb of intervening sequences. This mRNA, designated the large latency transcript, is 8.5 kb. It is polyadenylated and contains a large open reading frame capable of coding for a 200-kDa polypeptide. The direction of transcription is antiparallel to that of the immediate-early gene IE180 and a newly identified early gene, EP0. The latency transcript overlaps the entire IE180 gene and most of the EP0 gene. The EP0 mRNA is 1.75 kb and polyadenylated. The deduced amino acid sequence revealed the presence of cysteine-rich zinc finger domain similar to that of the immediate-early gene ICP0 of herpes simplex virus type 1 and the gene 61 polypeptide of varicella-zoster virus. On the basis of the biological functions, conserved protein domains, and unique spatial arrangements of the homologous polypeptides (IE180 versus ICP4 and EP0 versus ICP0) between pseudorabies virus and herpes simplex virus type 1, it is predicted that a homologous protein domain is also encoded by the 8.5-kb large latency transcripts of these two viruses.
Amino Acid Sequence↗
Genetic analysis of porcine respiratory coronavirus, an attenuated variant of transmissible gastroenteritis virus.
The genome and transcriptional pattern of a newly identified respiratory variant of transmissible gastroenteritis virus were analyzed and compared with those of classical enterotropic transmissible gastroenteritis virus. The transcriptional patterns of the two viruses indicated that differences occurred in RNAs 1 and 2(S) and that RNA 3 was absent in the porcine respiratory coronavirus (PRCV) variant. The smaller RNA 2(S) of PRCV was due to a 681-nucleotide (nt) deletion after base 62 of the PRCV peplomer or spike (S) gene. The PRCV S gene still retained information for the 16-amino-acid signal peptide and the first 6 amino acid residues at the N terminus of the mature S protein, but the adjacent 227 residues were deleted. Two additional deletions (3 and 5 nt) were detected in the PRCV genome downstream of the S gene. The 3-nt deletion occurred in a noncoding region; however, the 5-nt deletion shortened the potential open reading frame A polypeptide from 72 to 53 amino acid residues. Significantly, a C-to-T substitution was detected in the last base position of the transcription recognition sequence upstream of open reading frame A, which rendered RNA 3 nondetectable in PRCV-infected cell cultures.
Base Sequence↗
A prospective study on intradialytic symptoms associated with reuse of hemodialyzers.
The benefits and disadvantages of hemodialyzer reuse is controversial. While biochemical data have suggested potential benefits from reuse, there is dispute over the clinical impact on the patient. Limited data show that reuse is associated with less intradialytic symptoms compared to first use. We conducted a prospective study of acute symptoms during clinical dialysis using new and reused cellulose acetate membrane hollow-fiber dialyzers. A total of 106 sessions using new dialyzers and 871 sessions employing reused dialyzers were monitored. Dialyzers were processed with an automated machine using hydrogen peroxide and peroxyacetic acid as sterilants. We found that, compared to new ones, reused dialyzers were associated with a similar frequency of overall and specific symptoms. In addition, there was no difference in the magnitude of changes in blood pressure during and after the treatments between the two groups. We conclude that maintenance hemodialysis with reused cellulose acetate membrane dialyzers processed with hydrogen peroxide and peroxyacetic acid was not associated with more or fewer subjective symptoms than dialysis with new dialyzers.
Adult↗
Hemodialysis membrane biocompatibility: the case of erythropoietin.
Protein adsorption occurs upon blood exposure to hemodialysis membranes. While adsorption of certain proteins may be beneficial, adsorption of others may be undesirable. In the present study, we investigated the binding of recombinant human erythropoietin (rHuEPO) to different types of hemodialysis membranes in vitro. The amount of rHuEPO bound was dependent on the time of incubation, the concentration of the protein offered and the membrane material. Membranes made from the copolymer of polyacrylonitrile and methallyl sulfonate (AN69) bound the greatest quantity of rHuEPO. The dose-response curve of the binding to this type of membrane was linear. At the highest concentration examined, AN69 membranes bound 30 times more rHuEPO than did Cuprophan. This amount bound to AN69 was also greater than that which is expected to be present in a monolayer covering the nominal membrane surface area. We conclude that, under certain conditions, the binding of rHuEPO can be substantial and represents an example in which protein binding to hemodialysis membrane may be disadvantageous.
Acrylic Resins↗
Prescribing hemodialysis using a weekly urea mass balance model.
Prescribing hemodialysis by monitoring only predialysis BUN concentrations is not sufficient to guarantee adequate therapy. Results from the National Cooperative Dialysis Study have suggested that hemodialysis therapy is adequate if the protein catabolic rate is maintained greater than 1 g/day/kg body weight and simultaneously if sufficient hemodialysis is prescribed to maintain either a time-averaged BUN concentration (TACurea) less than 50 mg/dl or a value of Kt/V greater than unity. In the present study mathematical relationships were derived from a weekly urea mass balance model that permit an evaluation of TACurea and of protein catabolism via the urea generation rate (G) without the need for conventional urea kinetic modeling. The parameters TACurea and G were simply calculated from a midweek predialysis BUN concentration (BUNMW) by: TACurea = 0.7 BUNMW G = 0.7 BUNMW(Kr + Kd tau/T) where Kr, Kd, tau and T denote residual renal urea clearance, dialyzer urea clearance, number of minutes of hemodialysis per week, and number of minutes total in a week, respectively. Clinical results from 139 modeling sessions on 91 patients demonstrated that TACurea and G derived from urea kinetic modeling correlated highly with those calculated from the above equations (r = 0.96 and 0.94, respectively). It is concluded that individualized hemodialysis prescription and adequacy of therapy can be assessed by monitoring TACurea and G by calculation from a weekly urea mass balance model.
Adult↗
Biomedical polymers differ in their capacity to activate complement.
Conventionally, complement activation by biomedical polymers has been evaluated by determining the C3a concentration in the fluid phase only. According to this criterion, biomaterials such as hemodialysis membranes made from cellulosic or various synthetic polymers were classified as activators or nonactivators of complement. Since certain membranes bind large quantities of C3a from the fluid phase, classification based on fluid-phase C3a concentration has in some instances been inaccurate. As follows from the comparison of complement activation by cuprophane and polyacrylonitrile membranes, the capacity of a biomedical polymer to activate complement is not determined by the number of potential covalent binding sites on its surface. Biomaterial itself may lack hydroxyl and/or amino groups, and yet it may activate C3 in human serum very efficiently. Some of the biomaterials may also bind unactivated/unfragmented C3 whether in the absence or presence of other serum proteins. In addition, binding of factor B (a promotor of C3 activation) and binding of factor H (an inhibitor of C3 activation) to certain biomaterials have been found to be independent of complement activation and unaffected by the presence or absence of C3. Thus, it is becoming apparent that the requirements for the formation and stability of the C3 convertase on artificial surfaces differ from those on biological membranes, and that the relative magnitude of binding of factor B and factor H to the surface per se cannot be used as a reliable indicator of the capacity of the biomaterial to activate complement. Further studies are necessary to elucidate the molecular mechanisms of C3 and C5 activation on the surfaces of biomedical polymers.(ABSTRACT TRUNCATED AT 250 WORDS)
Blood Proteins↗
Update and comparison of the immediate-early gene DNA sequences of two pseudorabies virus isolates.
Differences between the immediate-early gene DNA sequences of two pseudorabies virus isolates (Indiana-Funkhauser and Ka) were resolved and confirmed. The deduced amino acid sequences showed that regions 2 and 4 have fewer changes than the rest of the molecules. These two conserved regions may be functionally important.
Amino Acid Sequence↗
Activation of complement by hemodialysis membranes: polyacrylonitrile binds more C3a than cuprophan.
Conventionally, complement activation by hemodialysis membranes has been determined by measuring fluid phase C3a. Based on such measurements, polyacrylonitrile (PAN) membranes have been classified as weak activators compared to cuprophan. Previous studies have demonstrated, however, that PAN adsorb fluid phase C3a. Based on that observation, we hypothesized that complement activation by PAN might be artifactually underestimated if relatively large amounts of C3a remained membrane bound. In the present study, a method that allows the simultaneous quantification of both fluid phase and membrane bound C3a was used to assess complement activation by PAN and cuprophan. Pieces of membrane were incubated with C3-depleted serum that had been repleted with radiolabeled C3. Subsequently, the supernates and membranes were subjected to SDS-PAGE, and complement activation was quantified by determining the radioactivity of the C3a bands in the gel. The results showed that while the serum exposed to cuprophan membranes contained almost five times more C3a than that exposed to PAN, approximately 80 times more C3a was bound to the PAN membranes. Consequently, the total amount of C3a generated in the presence of PAN was higher than that generated in the presence of cuprophan. We conclude that assessment of complement activation by hemodialysis membranes using fluid phase C3a measurements alone may be misleading.
Acrylic Resins↗
Genetic basis for the pathogenesis of transmissible gastroenteritis virus.
Intracellular RNAs of an avirulent small-plaque (SP) transmissible gastroenteritis virus variant and the parent virulent Miller strain of transmissible gastroenteritis virus were compared. Northern RNA blotting showed that the Miller strain contained eight intracellular RNA species. RNAs 1, 2(S), 5, 6(M), 7(N), and 8 were similar in size for both viruses; however, the SP variant lacked subgenomic RNAs 3 and 4. Instead, the SP virus contained an altered RNA species (delta 4) that was slightly smaller than RNA 4. S1 nuclease protection experiments showed a deletion of approximately 450 nucleotides in the SP genome downstream of the peplomer S gene. Sequencing of cDNA clones confirmed that SP virus contained a 462-nucleotide deletion, eliminating the transcriptional recognition sequences for both RNAs 3 and 4. These RNAs encode open reading frames A and B, respectively. An alternative consensus recognition sequence was not readily apparent for the delta 4 RNA species of SP virus. Since open reading frame A is missing in SP virus, it is not essential for a productive infection. The status of the potential protein encoded by open reading frame B is not clear, because it may be missing or just truncated. Nevertheless, these genes appear to be the contributing entities for transmissible gastroenteritis virus virulence, SP morphology, tissue tropism, and/or persistence in swine leukocytes.
Animals↗
The BamHI J fragment (0.706 to 0.737 map units) of pseudorabies virus is transcriptionally active during viral replication.
The BamHI J fragment of the pseudorabies virus (PRV) genome has not been associated with any viral transcripts during viral replication. In this report, data are presented to show that a portion of BamHI-J is transcribed during a productive infection. Four oligo(dT)-cellulose-selected RNA species were detected by hybridization with probes derived from BamHI-J. These RNAs were partially colinear, and they were transcribed in the opposite orientation with respect to the immediate-early gene (IE180) of PRV. At least one of the transcripts overlapped (antisense) the coding sequence of IE180 by 450 nucleotides. Expression of these RNAs was sensitive to phosphonoacetic acid, indicating that they are transcripts of PRV late genes. There were several similarities between these RNAs and the latency-associated transcripts detected in the trigeminal ganglia of swine latently infected with PRV (A. K. Cheung, J. Virol. 63: 2908-2913, 1989).
Animals↗
Biocompatibility of hemodialysis membranes.
Exposure of blood to hemodialysis membranes results in numerous interactions between the blood elements and the membrane. Transformation and adsorption of plasma proteins (such as complement) and activation of blood cells (such as neutrophils and monocytes) have been studied most extensively by nephrologists in recent years. There is no consensus on the definition of biocompatibility for dialyzer membranes. An operational definition of biocompatibility is the lack of any perturbation of blood constituents. According to this "inert surface" definition, a membrane (for example, one that adsorbs beta 2-microglobulin) can be considered as bioincompatible and yet desirable. Because of the multitude of blood-membrane interactions that may occur during hemodialysis, multiple criteria for biocompatibility needs to be applied in the classification of membranes. A certain bioincompatible phenomenon can be further classified as beneficial or deleterious depending on its biological effects as well as its acute and chronic impacts on the dialysis patient.
Biocompatible Materials↗
Humoral immune response to immediate-early protein of pseudorabies virus in swine with induced or naturally acquired infection.
Pseudorabies virus (PRV) immediate-early (IE) protein is a nonglycosylated polypeptide localized in the nuclei of infected cells. The IE protein is a regulatory protein that is only synthesized during viral replication and is presented to the immune system of PRV-infected swine. Antibodies to the IE protein were demonstrated in swine with induced or naturally acquired infection. However, antiserum raised against purified IE protein could not neutralize PRV in vitro.
Animals↗
DNA nucleotide sequence analysis of the immediate-early gene of pseudorabies virus.
The complete DNA sequence coding for the immediate-early protein (IE180) of pseudorabies virus was determined. The coding region of IE180 is 4380 nucleotides for 1460 amino acid residues. G+C content of the non-coding portion of the IE gene is 70.3% while the G+C content of the coding portion is considerably higher at 80.1%. Correspondingly, codons consisting mainly of Gs and Cs are favoured. Clusters of amino acid homologies are observed among IE180 of pseudorabies virus, ICP4 of herpes simplex virus type-1 and IE140 of varicella-zoster virus, and are organized similarly in all three polypeptides. Functions exhibited by IE180 are assigned, tentatively, to structural domains of the molecule by analogy to the HSV-1 ICP4 polypeptide.
Amino Acid Sequence↗
Nucleotide sequence of coronavirus TGEV genomic RNA: evidence for 3 mRNA species between the peplomer and matrix protein genes.
The region of the TGEV genome between the E1-matrix protein gene and the E2-peplomer protein gene has been sequenced from a cDNA clone. The consensus recognition sequence, 5'TTAA CTAAAC was found upstream from 3 large open reading frames. In coronaviruses these homologous recognition sequences are involved in the initiation of transcription suggesting that there are 3 mRNA species in this region of the TGEV genome. Northern blot analysis and nuclease S1 mapping confirmed the presence of 3 mRNA species between mRNA 3 encoding the E2-peplomer protein and mRNA 6 encoding the E1-matrix protein. The 5' regions of these 3 mRNAs encode potential polypeptides of predicted molecular weight; 7859, 27744 and 9287, respectively. The potential translation product of ORF B (27744 Da) is considerably larger than previously reported and could be difficult to distinguish by size from the E1-matrix protein.
Animals↗