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R Rieben

Publications and source records attributed to R Rieben.

30 records · Page 2Linked to original sources
PubMed1996

Biocompatibility in transfusion medicine.

The first measurable event upon interaction of artificial surfaces with blood is adsorption of proteins within seconds or minutes. At a later stage, blood cells interact with the surfaces through the initially deposited protein layer. The chemical composition of the surface is only one criterion for differential deposition of various plasma proteins, with molecular motion (polymer chain ends, loops and their flexibility), and topography (roughness, porosity) of the surface decisively influencing the interactions as well. Initially incompatible surfaces, which may be dangerous to the patient, may be rendered compatible by physicochemical surface modifications. Modern methods to estimate biocompatibility have become so sensitive that they may detect biological modifications of the blood after contact with a surface, which has no consequence for the patient. In these cases it is often difficult to decide whether a material should be classified as biocompatible or non-biocompatible. This paper discusses some methods that we have used for the study of biocompatibility of extracorporeal circuitry. It seems to us that minute signs of laboratory evidence for bioincompatibility should not preclude usage of the material in a clinical setting.

Biocompatible Materials↗
PubMed1995

In vitro evaluation of the efficacy and biocompatibility of new, synthetic ABO immunoabsorbents.

Synthetic ABO immunoabsorbents (known as Synsorbs) were in use for several years to specifically eliminate ABO antibodies from the patient's circulation before ABO-incompatible organ or bone marrow transplantation. Because Synsorbs are no longer available, we have developed new ABO immunoabsorbents. These substances, termed BioSorbents A and B, respectively, consist of synthetic A or B trisaccharides covalently coupled to macroporous glass beads via polyacrylamide. Here we report the evaluation of BioSorbents in regard to efficacy, specificity, and biocompatibility. Using a closed-circuit in vitro system, representing a 1:10-1:20 scale as compared with the immunoabsorption procedure with an adult patient, blood group O plasma was run through columns filled with ethylene oxide-sterilized BioSorbent. Hemagglutination was reduced by 4 titer steps after absorption, and anti-A and/or anti-B IgM/G/A, as measured by ABO ELISA, dropped by 85% or more, while no nonspecific absorption of immunoglobulins occurred. No significant changes could be observed for complement (C3, C4, and total hemolytic complement of the classical pathway) or for coagulation parameters (fibrinogen, prothrombin time, activated partial thromboplastin time). As monitored by immunoblotting, neither factor XII nor high molecular weight kininogen was cleaved. In addition, a monocyte phagocytosis inhibition test provided evidence that no significant aggregation of IgG had occurred during absorption. We conclude that BioSorbents A and B are efficient, specific, and biocompatible with human plasma.

ABO Blood-Group System↗
PubMed1994

Development of a C1q-ABO-ELISA to measure C1q binding by human anti-A alloantibodies.

Little is known about the correlation between the amount of anti-A antibodies and the respective complement activating capacity. We have therefore developed a new ELISA procedure for the study of complement activation by anti-A antibodies bound to immobilized blood group substance A through the classical pathway. C1q binding capacity of anti-A was then compared to both anti-A immunoglobulin (Ig) isotype serum concentrations and to the hemolysing capacity of O type sera. We have demonstrated that sera with low anti-A IgG and IgM levels produced low C1q binding activity and no hemolysis of human A1 red blood cells (RBC), whereas higher anti-A Ig levels resulted in either weak or strong C1q binding capacity as well as weak or strong RBC hemolysis. A correlation of rs = 0.755 was observed between C1q-ABO-ELISA and hemolysin assay results, although only 58% of the O type sera containing C1q binding anti-A lysed A1 type RBC under the used conditions. The C1q-ABO-ELISA is therefore a more sensitive assay for detecting 'dangerous' O type donors for blood transfusion to A type recipients than screening tests for hemolytic anti-A or determination of anti-A Ig levels alone.

ABO Blood-Group System↗
PubMed1992

Naturally occurring ABO antibodies: long-term stable, individually distinct anti-A IgG spectrotypes.

Spectrotypes of naturally occurring IgG antibodies to histo-blood group substance A were analyzed by isoelectric focusing and a newly developed, non-radioactive affinity immunoblotting assay. Specificity was tested by preabsorption of sera on red blood cells and on four different types of blood group substance A. Clonotype-banding patterns of sera from 18 different blood donors were individually distinct, most of them showing an oligoclonal pattern with less than 15 visible bands. To analyze the influence of IgG subclass composition on spectrotype patterns, IgG subclasses were measured by ABO enzyme-linked immunosorbent assay (ELISA) and were shown to be mostly IgG1 and IgG2. Anti-A IgG1 spectrotypes could be detected with four sera and were also individually distinct. A series of six and seven serum samples, respectively from two donors was used to analyze the time-related changes of anti-A IgG spectrotypes. Banding pattern of both individuals remained stable during the whole observation period of 167 and 82 days, respectively, and no differences between follow-up samples could be detected. This long-term stability of individual anti-A IgG spectrotypes is backed by constant serum levels of anti-A IgG and -IgM antibodies during the observation period as measured by ABO ELISA.

ABO Blood-Group System↗
PubMed1992

Self tolerance to human A and B histo-blood group antigens exists at the B cell level and cannot be broken by potent polyclonal B cell activation in vitro.

It is generally considered that tolerance to self antigens is less complete in B than in T lymphocytes. However, B cell tolerance through either functional inactivation (anergy) or clonal deletion has been demonstrated in transgenic mice. In the present study, we investigated whether B cells specific for self A/B histo-blood group antigens can be detected in normal humans. It is a key feature of the ABO system that all normal individuals make natural antibodies against those A or B carbohydrates which are not present in their organism. To detect B cells by the limiting dilution approach we used a specific enzyme-linked immunosorbent assay for the quantitation of anti-A/B antibodies, and a culture system in which polyclonal B cell activation occurs through cell contact with EL4 thymoma cells. As was reported for other B cell studies, we frequently detected "polyreactive" immunoglobulin (Ig)M (but not IgG) with apparent autoreactivity but of uncertain significance regarding physiologic conditions. However, A- or B-specific B cell responses occurred with selective patterns in agreement with classical blood group serology in 14 individuals with A, B, AB or 0 blood group phenotypes: 1/11,600 B cells made anti-allo A/B IgM and 1/26,500 B cells such as IgG, while only 1/104,000 B cells apparently made anti-self A/B IgM and 1/350,000 B cells such as IgG. This shows self tolerance at the B cell level. Since anergy of B cells can frequently be broken by polyclonal B cell activation in vitro, and EL4 cells are potent B cell stimulators, the present results argue for either a highly resistant anergic state or for clonal deletion of self-A/B histo-blood group-specific human B cells.

ABO Blood-Group System↗
PubMed1991

Antibodies to histo-blood group substances A and B: agglutination titers, Ig class, and IgG subclasses in healthy persons of different age categories.

Isotypes and IgG subclasses of ABO antibodies from sera of 235 healthy blood donors were determined by an enzyme-linked immunosorbent assay (ELISA). Synthetic A and B trisaccharide-bovine serum albumin glycoconjugates were used for coating and monoclonal antibodies for the detection of heavy chain isotypes. Hemagglutination titers were determined in addition. Blood donors were between 20 and 67 years old, and at least 10 sera per 10-year age category and ABO blood group were included in this study. Antibody concentrations were expressed as a percentage of an internal standard, and sera with subclass-restricted anti-A and/or anti-B (anti-A/B) responses were used to normalize the ELISA values of IgG subclasses. A good correlation between the sum of the four subclasses and the total anti-A/B IgG values (rs = 0.81 for anti-A and 0.84 for anti-B) was obtained. IgG1 and IgG2 were the most predominant subclasses, but were found in various proportions in different individuals. Donor-to-donor variation exceeded age-related changes for all measured parameters. The correlation of anti-A IgM, IgG, IgA, and their sum with the agglutination titers was significant and revealed rs values of 0.70, 0.65, 0.65, and 0.80, respectively. For anti-B as well, the correlation of ELISA values with the agglutination titer was best when all three isotypes were added. We conclude that anti-A/B IgA, together with IgM and IgG, substantially contributes to the agglutination reaction. Potentially autoreactive antibodies were detected in sera of blood groups A, B, and AB.

ABO Blood-Group System↗
PubMed1989

Quantification of IgG and IgG4 antibodies to bee venom phospholipase A2 by competitive inhibition in ELISA.

Phospholipase A2 (PLA) is the major antigen of bee venom. Individuals often stung by bees, such as bee keepers, show a restricted immune response mainly of anti-PLA IgG4 antibodies. In contrast, patients allergic to bee venom produce high levels of PLA-specific IgE. This isotype restriction, the clinical relevance and the well defined structure of the PLA antigen, provide a useful model for the study of the principles regulating isotype expression in the human antibody response. A fundamental requirement for such studies is the availability of quantitative and sensitive assays to measure PLA-specific antibodies. Here we describe an ELISA method for direct isotype-specific quantification of anti-PLA IgG and IgG4 antibodies. Serum containing anti-PLA IgG antibodies was added at a predetermined dilution to PLA coated microtiter plates. Then mouse monoclonal antibodies to human IgG or IgG4 and different concentrations of purified human IgG and IgG4, respectively, were added simultaneously. The concentration of anti-PLA IgG and IgG4 antibodies in the serum was calculated from the resulting inhibition curve. Additionally, an analytical method to compare unknown antibody samples with a standard in ELISA - avoiding problems of different affinities - is described. Using the technique described here, isotype-specific quantification of anti-PLA antibodies can be performed at a sensitivity of approximately 70 pg/ml with a reproducibility range of 10-15%.

Adult↗
PubMedDate not supplied

[Neoglycoconjugates based on dendrimeric poly(aminoamides)].

Neoglycoconjugates containing 4, 8, 16, 32, and 64 terminal residues of B-disaccharide (BDI) or N-acetylneuraminic acid (Neu5Ac) attached to poly(aminoamide)-type dendrimers (PAMAMs) were synthesized. The ability of BDI conjugates to bind natural xenoantibodies (anti-BDI antibodies) and the ability of Neu5Ac conjugates to inhibit the hemagglutinin-mediated adhesion of influenza virus were studied. The biological activity of PAMAM conjugates turned out to be higher than that of free carbohydrate ligands, but less than that of multivalent glycoconjugates based on other types of synthetic polymeric carriers. A conformational analysis of PAMAM matrices and resulting conjugates was performed to determine the statistical distances between carbohydrate ligands. The computations revealed the tendency of the PAMAM chains toward compaction and formation of dense globules. The process results in a decrease in the distances between the carbohydrate ligands in the conjugates and, hence, could affect the ability of glycoconjugates to efficiently bind the polyvalent carbohydrate-recognizing proteins. The English version of the paper: Russian Journal of Bioorganic Chemistry, 2002, vol. 28, no. 6; see also http://www.maik.ru.

Antibodies, Heterophile↗
PubMedDate not supplied

Age dependency of ABO histo-blood group antibodies: reexamination of an old dogma.

Current textbooks for transfusion medicine state that anti-A and/or anti-B (anti-A/B) agglutination titers--and thus the respective antibody concentrations--reach their maximum in individuals 5 to 10 years old and then gradually decline with the increasing age of the individual. This statement is largely based on a study by Thomsen and Kettel that dates to 1929. In the present article, ABO antibodies in sera of 175 healthy persons aged 61 to 97 years, as well as sera of 170 newborn infants and children aged 0 to 17 years, were analyzed. Microhemagglutination tests were performed with all sera and complemented by ABO enzyme-linked immunosorbent assays to measure the immunoglobulin class (IgM, IgG, and IgA) of the anti-A/B. As in a previous study using sera of persons aged 20 to 67 years, individual differences exceeded age-related changes for all variables. Median values of IgG and IgA anti-A/B were elevated in elderly persons of blood group O, whereas no significant changes were observed in other variables. In particular, the decrease in agglutination titers with the increasing age of the individuals was far less pronounced than previously described; even in sera of persons aged 90 to 97 years, median agglutination titers of 128 were found. Results in the sera of children confirm previously reported data that agglutination titers and IgM anti-A/B reached adult levels at the age of 5 to 10 years.

ABO Blood-Group System↗