Erythro-VLPs: Anchoring SARS-CoV-2 spike proteins in erythrocyte liposomes

Novel therapeutic strategies are needed to control the SARS-CoV-2 (severe acute respiratory syndrome coronavirus 2) pandemic. Here, we present a protocol to anchor the SARS-CoV-2 spike (S-)protein in the cytoplasmic membranes of erythrocyte liposomes. A surfactant was used to stabilize the S-protein’s structure in the aqueous environment before insertion and to facilitate reconstitution of the S-proteins in the erythrocyte membranes. The insertion process was studied using coarse grained Molecular Dynamics (MD) simulations. Liposome formation and S-protein anchoring was studied by dynamic light scattering (DLS), ELV-protein co-sedimentation assays, fluorescent microcopy and cryo-TEM. The Erythro-VLPs (erythrocyte based virus like particles) have a well defined size of ∼200 nm and an average protein density on the outer membrane of up to ∼300 proteins/μm². The correct insertion and functional conformation of the S-proteins was verified by dose-dependent binding to ACE-2 (angiotensin converting enzyme 2) in biolayer interferometry (BLI) assays. Seroconversion was observed in a pilot mouse trial after 14 days when administered intravenously, based on enzyme-linked immunosorbent assays (ELISA). This red blood cell based platform can open novel possibilities for therapeutics for the coronavirus disease (COVID-19) including variants, and other viruses in the future.

Erythrocytes: Central Actors in Multiple Scenes of Atherosclerosis

The development and progression of atherosclerosis (ATH) involves lipid accumulation, oxidative stress and both vascular and blood cell dysfunction. Erythrocytes, the main circulating cells in the body, exert determinant roles in the gas transport between tissues. Erythrocytes have long been considered as simple bystanders in cardiovascular diseases, including ATH. This review highlights recent knowledge concerning the role of erythrocytes being more than just passive gas carriers, as potent contributors to atherosclerotic plaque progression. Erythrocyte physiology and ATH pathology is first described. Then, a specific chapter delineates the numerous links between erythrocytes and atherogenesis. In particular, we discuss the impact of extravasated erythrocytes in plaque iron homeostasis with potential pathological consequences. Hyperglycaemia is recognised as a significant aggravating contributor to the development of ATH. Then, a special focus is made on glycoxidative modifications of erythrocytes and their role in ATH. This chapter includes recent data proposing glycoxidised erythrocytes as putative contributors to enhanced atherothrombosis in diabetic patients.

Band 3 ectopic expression in colorectal cancer induces an increase in erythrocyte membrane-bound IgG and may cause immune-related anemia

Autoimmune hemolytic anemia (AIHA) is a rare comorbidity in colorectal cancer (CRC) and has an unknown etiology. Previously, we described an AIHA case secondary to CRC with ectopic band 3 expression. Herein, we investigated ectopic band 3 expression and erythrocyte membrane-bound IgG in a CRC cohort. Between September 2016 and August 2018, 50 patients with CRC and 26 healthy controls were enrolled in the present study. The expression of band 3 and SLC4A1 mRNA was observed in 97% of CRC surgical specimens. Although clinical AIHA was not observed in any patient with CRC, a direct antiglobulin test was positive in 10 of the patients in the CRC group (p = 0.01). Flow cytometry revealed significantly increased erythrocyte membrane-bound IgG among patients with CRC compared to healthy controls (mean ± standard deviation; 38.8 ± 4.7 vs. 29.9 ± 15.6, p = 0.012). Normocytic anemia was observed, including in cases negative for fecal occult blood, suggesting a shortened erythrocyte life-span due to increased membrane-bound IgG. Immunoprecipitation revealed increased anti-band 3 autoantibodies in patients' sera. Mouse experiments recapitulated this phenomenon. We also confirmed that band 3 expression is controlled by 5'AMP-activated protein kinase under hypoxic conditions. These findings increase our understanding of the etiology of cancer-related anemia.

Antigenic cartography of immune responses to Plasmodium falciparum erythrocyte membrane protein 1 (PfEMP1)

Naturally acquired clinical immunity to Plasmodium falciparum is partly mediated by antibodies directed at parasite-derived antigens expressed on the surface of red blood cells which mediate disease and are extremely diverse. Unlike children, adults recognize a broad range of variant surface antigens (VSAs) and are protected from severe disease. Though crucial to the design and feasibility of an effective malaria vaccine, it is not yet known whether immunity arises through cumulative exposure to each of many antigenic types, cross-reactivity between antigenic types, or some other mechanism. In this study, we measured plasma antibody responses of 36 children with symptomatic malaria to a diverse panel of 36 recombinant proteins comprising part of the DBLα domain (the 'DBLα-tag') of PfEMP1, a major class of VSAs. We found that although plasma antibody responses were highly specific to individual antigens, serological profiles of responses across antigens fell into one of just two distinct types. One type was found almost exclusively in children that succumbed to severe disease (19 out of 20) while the other occurred in all children with mild disease (16 out of 16). Moreover, children with severe malaria had serological profiles that were narrower in antigen specificity and shorter-lived than those in children with mild malaria. Borrowing a novel technique used in influenza-antigenic cartography-we mapped these dichotomous serological profiles to amino acid sequence variation within a small sub-region of the PfEMP1 DBLα domain. By applying our methodology on a larger scale, it should be possible to identify epitopes responsible for eliciting the protective version of serological profiles to PfEMP1 thereby accelerating development of a broadly effective anti-disease malaria vaccine.

Delivery of drugs bound to erythrocytes: new avenues for an old intravascular carrier

For several decades, researchers have used erythrocytes for drug delivery of a wide variety of therapeutics in order to improve their pharmacokinetics, biodistribution, controlled release and pharmacodynamics. Approaches include encapsulation of drugs within erythrocytes, as well as coupling of drugs onto the red cell surface. This review focuses on the latter approach, and examines the delivery of red blood cell (RBC)-surface-bound anti-inflammatory, anti-thrombotic and anti-microbial agents, as well as RBC carriage of nanoparticles. Herein, we discuss the progress that has been made in surface loading approaches, and address in depth the issues relevant to surface loading of RBC, including intrinsic features of erythrocyte membranes, immune considerations, potential surface targets and techniques for the production of affinity ligands.

An alternative chemical redox method for the production of bispecific antibodies: implication in rapid detection of food borne pathogens

Bi-functional antibodies with the ability to bind two unrelated epitopes have remarkable potential in diagnostic and bio-sensing applications. In the present study, bispecific antibodies that recognize human red blood cell (RBC) and the food borne pathogen Listeria monocytogenes (L. monocytogenes) were engineered. The procedure involves initial reduction of a mixture of anti-RBC and anti-Listeria antibodies followed by gradual re-oxidation of the reduced disulphides. This facilitates association of the separated antibody chains and formation of hybrid immunoglobulins with affinity for the L. monocytogenes and human RBC. The bispecific antibodies caused the agglutination of the RBCs only in the presence of L. monocytogenes cells. The agglutination process necessitated the specific presence of L. monocytogenes and the red colored clumps formed were readily visible with naked eyes. The RBC agglutination assay described here provides a remarkably simple approach for the rapid and highly specific screening of various pathogens in their biological niches.

A lytic mechanism based on soluble phospholypases A2 (sPLA2) and β-galactoside specific lectins is exerted by Ciona intestinalis (ascidian) unilocular refractile hemocytes against K562 cell line and mammalian erythrocytes

Hemocytes from the ascidian Ciona intestinalis exert in vitro Ca²+-dependent cytotoxic activity toward mammalian erythrocytes and K562 cells. To examine the lytic mechanism, hemocyte populations were separated (B1-B6 bands) through a Percoll discontinuous density gradient, the hemocyte cytotoxic activity (HCA) and the lytic activity of the hemocyte lysate supernatant (HLS) were assayed. In addition the separated hemocytes were cultured and the cell-free culture medium (CFM) assayed after 3 h culture. Results support that unilocular refractile hemocytes (URGs), enriched in B5, are cytotoxic. The B5-HLS contains lysins and the activity of B5-CFM shows that lysins can be released into a culture medium. The B5 activity was blocked by D-galactose, α-lactose, lactulose, LacNAc, thiodigalactoside (TDG), L-fucose, D-mannose, D-glucose, sphingomyelin (SM), and soluble phospholipase A2 (sPLA2) inhibitors (dibucain, quinacrine). Accordingly, HLS chemico-physical properties (alkaline medium, high thermostability, Ca²+-dependence, trypsin treatment, protease inhibitors) and SEM observations of the affected targets suggested that sPLA2 could be responsible for changes and large alterations of the target cell membrane. An apoptotic activity, as recorded by a caspase 3, 7 assay, was found by treating K562 cells with very diluted HLS. A lytic mechanism involving sPLA2 and lectins promptly released by URGs and morula cells respectively is suggested, whereas target cell membrane SM could be a modulator of the enzyme activity.

Allelic diversity of the Plasmodium falciparum erythrocyte membrane protein 1 entails variant-specific red cell surface epitopes

The clonally variant Plasmodium falciparum PfEMP1 adhesin is a virulence factor and a prime target of humoral immunity. It is encoded by a repertoire of functionally differentiated var genes, which display architectural diversity and allelic polymorphism. Their serological relationship is key to understanding the evolutionary constraints on this gene family and rational vaccine design. Here, we investigated the Palo Alto/VarO and IT4/R29 and 3D7/PF13_003 parasites lines. VarO and R29 form rosettes with uninfected erythrocytes, a phenotype associated with severe malaria. They express an allelic Cys2/group A NTS-DBL1α₁ PfEMP1 domain implicated in rosetting, whose 3D7 ortholog is encoded by PF13_0003. Using these three recombinant NTS-DBL1α₁ domains, we elicited antibodies in mice that were used to develop monovariant cultures by panning selection. The 3D7/PF13_0003 parasites formed rosettes, revealing a correlation between sequence identity and virulence phenotype. The antibodies cross-reacted with the allelic domains in ELISA but only minimally with the Cys4/group B/C PFL1955w NTS-DBL1α. By contrast, they were variant-specific in surface seroreactivity of the monovariant-infected red cells by FACS analysis and in rosette-disruption assays. Thus, while ELISA can differentiate serogroups, surface reactivity assays define the more restrictive serotypes. Irrespective of cumulated exposure to infection, antibodies acquired by humans living in a malaria-endemic area also displayed a variant-specific surface reactivity. Although seroprevalence exceeded 90% for each rosetting line, the kinetics of acquistion of surface-reactive antibodies differed in the younger age groups. These data indicate that humans acquire an antibody repertoire to non-overlapping serotypes within a serogroup, consistent with an antibody-driven diversification pressure at the population level. In addition, the data provide important information for vaccine design, as production of a vaccine targeting rosetting PfEMP1 adhesins will require engineering to induce variant-transcending responses or combining multiple serotypes to elicit a broad spectrum of immunity.

Disease-associated glycosylated molecular variants of human C-reactive protein activate complement-mediated hemolysis of erythrocytes in tuberculosis and Indian visceral leishmaniasis

Human C-reactive protein (CRP), as a mediator of innate immunity, removed damaged cells by activating the classical complement pathway. Previous studies have successfully demonstrated that CRPs are differentially induced as glycosylated molecular variants in certain pathological conditions. Affinity-purified CRPs from two most prevalent diseases in India viz. tuberculosis (TB) and visceral leishmaniasis (VL) have differential glycosylation in their sugar composition and linkages. As anemia is a common manifestation in TB and VL, we assessed the contributory role of glycosylated CRPs to influence hemolysis via CRP-complement-pathway as compared to healthy control subjects. Accordingly, the specific binding of glycosylated CRPs with erythrocytes was established by flow-cytometry and ELISA. Significantly, deglycosylated CRPs showed a 7-8-fold reduced binding with erythrocytes confirming the role of glycosylated moieties. Scatchard analysis revealed striking differences in the apparent binding constants (10(4)-10(5) M(-1)) and number of binding sites (10(6)-10(7)sites/erythrocyte) for CRP on patients' erythrocytes as compared to normal. Western blotting along with immunoprecipitation analysis revealed the presence of distinct molecular determinants on TB and VL erythrocytes specific to disease-associated CRP. Increased fragility, hydrophobicity and decreased rigidity of diseased-erythrocytes upon binding with glycosylated CRP suggested membrane damage. Finally, the erythrocyte-CRP binding was shown to activate the CRP-complement-cascade causing hemolysis, even at physiological concentration of CRP (10 microg/ml). Thus, it may be postulated that CRP have a protective role towards the clearance of damaged-erythrocytes in these two diseases.

The Dombrock blood group system: a review

The Dombrock blood group system (Do) consists of two antithetical antigens (Do(a) and Do(b)) and five antigens of high prevalence (Gy(a), Hy, Jo(a), DOYA, and DOMR). Do antigens are carried on the Dombrock glycoprotein, which is attached to the RBC membrane via glycosylphosphatidylinositol linkage. The gene (DO, ART4) encoding the Do glycoprotein, located on the short arm of chromosome 12, has been cloned and sequenced, allowing the molecular basis of the various Do phenotypes to be determined. Do(a) and Do(b) have a prevalence that makes them useful as genetic markers; however, the paucity of reliable anti-Do(a) and anti-Do(b) has prevented this potential from being realized. The ease with which these antigens can be predicted by analysis of DNA opens the door for such studies to be carried out. Anti-Do(a) and anti-Do(b) are rarely found as a single specificity, but they have been implicated in causing hemolytic transfusion reactions. This review is a synthesis of our current knowledge of he Dombrock blood group system.

Presence of horse blood group antigens in the major glycoprotein fraction of the erythrocyte membrane

The aqueous phase of the chloroform/methanol extract of the horse erythrocyte membrane contained the blood group activities Ad, Dc or Dd. The factors Ad and Dc could be separated by gel filtration.

High throughput functional assays of the variant antigen PfEMP1 reveal a single domain in the 3D7 Plasmodium falciparum genome that binds ICAM1 with high affinity and is targeted by naturally acquired neutralizing antibodies

Plasmodium falciparum–infected erythrocytes bind endothelial receptors to sequester in vascular beds, and binding to ICAM1 has been implicated in cerebral malaria. Binding to ICAM1 may be mediated by the variant surface antigen family PfEMP1: for example, 6 of 21 DBLβC2 domains from the IT4 strain PfEMP1 repertoire were shown to bind ICAM1, and the PfEMP1 containing these 6 domains are all classified as Group B or C type. In this study, we surveyed binding of ICAM1 to 16 DBLβC2 domains of the 3D7 strain PfEMP1 repertoire, using a high throughput Bioplex assay format. Only one DBL2βC2 domain from the Group A PfEMP1 PF11_0521 showed strong specific binding. Among these 16 domains, DBL2βC2_{PF11_0521} best preserved the residues previously identified as conserved in ICAM1-binding versus non-binding domains. Our analyses further highlighted the potential role of conserved residues within predominantly non-conserved flexible loops in adhesion, and, therefore, as targets for intervention. Our studies also suggest that the structural/functional DBLβC2 domain involved in ICAM1 binding includes about 80 amino acid residues upstream of the previously suggested DBLβC2 domain. DBL2βC2_{PF11_0521} binding to ICAM1 was inhibited by immune sera from east Africa but not by control US sera. Neutralizing antibodies were uncommon in children but common in immune adults from east Africa. Inhibition of binding was much more efficient than reversal of binding, indicating a strong interaction between DBL2βC2_{PF11_0521} and ICAM1. Our high throughput approach will significantly accelerate studies of PfEMP1 binding domains and protective antibody responses.

Plasmodium falciparum exports the protein PfEMP1 to the surface of parasitized erythrocytes for roles in immunoevasion and adhesion. The size and structural complexity of this diverse protein family have limited earlier studies of PfEMP1 biology to low throughput and semi-quantitative approaches. We developed a high throughput quantitative assay of PfEMP1 adhesion and used it to analyze structural features of domains that bind the putative cerebral receptor ICAM1, as well as to survey the acquisition of functional antibodies in malaria-exposed children and adults. In studies of the PfEMP1 repertoire of clone 3D7 parasites, a single specific domain bound ICAM1 strongly. PfEMP1 domains that bind ICAM1 strongly have conserved features, including conserved amino acids within otherwise highly variant flexible loops of the protein. While neutralizing antibodies against the PfEMP1–ICAM1 interaction were uncommon in Tanzanian children, such antibodies were common in east African adults, possibly explaining why immune adults rarely carry ICAM1-binding parasites. This high throughput platform will significantly accelerate studies of PfEMP1 binding domains and the corresponding antibody responses involved in protective immunity.

Cut-off value of red-blood-cell-bound IgG for the diagnosis of Coombs-negative autoimmune hemolytic anemia

Direct antiglobulin test (DAT)-negative autoimmune hemolytic anemia (Coombs-negative AIHA) is characterized by laboratory evidence of in vivo hemolysis, together with a negative DAT performed by conventional tube technique (CTT) in clinically suspected AIHA patients. The immunoradiometric assay (IRMA) for red-blood-cell-bound immunoglobulin G (RBC-IgG) can be used to diagnose patients in whom CTT does not detect low levels of red cell autoantibodies. We investigated the diagnostic cutoff value of the IRMA for RBC-IgG in Coombs-negative AIHA and calculated its sensitivity and specificity. Of the 140 patients with negative DAT by CTT referred to our laboratory with undiagnosed hemolytic anemia, AIHA was clinically diagnosed in 64 patients (Coombs-negative AIHA). The numbers of Coombs-negative AIHA and non-AIHA patients changed with age and gender. The cutoff values were determined from receiver operating characteristic (ROC) curve according to age and gender. The IRMA for RBC-IgG proved to be sensitive (71.4%) and specific (87.8%) when using these cutoffs. Using these cutoffs for 41 patients with negative DAT referred to our laboratory in 2006, all the pseudonegative cases were treated with steroids before the test. The 31 untreated cases could be grouped using one cutoff value of 78.5 and showed 100% sensitivity and 94% specificity, independent of gender and age. Results indicate that RBC-IgG could become a standard approach for the diagnosis of Coombs-negative AIHA, when measured before treatment.

Mechanisms of anti-D action in the prevention of hemolytic disease of the fetus and newborn

Anti-D is routinely and effectively used to prevent hemolytic disease of the fetus and newborn (HDFN) caused by the antibody response to the D antigen on fetal RBCs. Anti-D is a polyclonal IgG product purified from the plasma of D-alloimmunized individuals. The mechanism of anti-D has not been fully elucidated. Antigenic epitopes are not fully masked by anti-D and are available for immune system recognition. However, a correlation has frequently been observed between anti-D-mediated RBC clearance and prevention of the antibody response, suggesting that anti-D may be able to destroy RBCs without triggering the adaptive immune response. Anti-D-opsonized RBCs may also elicit inhibitory FcgammaRIIB signaling in B cells and prevent B cell activation. The ability of antigen-specific IgG to inhibit antibody responses has also been observed in a variety of animal models immunized with a vast array of different antigens, such as sheep RBCs (SRBC). This effect has been referred to as antibody-mediated immune suppression (AMIS). In animal models, IgG inhibits the antibody response, but the T-cell response and memory may still be intact. IgG does not mask all epitopes, and IgG-mediated RBC clearance or FcgammaRIIB-mediated B-cell inhibition do not appear to mediate the AMIS effect. Instead, IgG appears to selectively disrupt B cell priming, although the exact mechanism remains obscure. While the applicability of animal models of AMIS to understanding the true mechanism of anti-D remains uncertain, the models have nevertheless provided us with insights into the possible IgG effects on the immune response.

Drug-induced immune hemolytic anemia

Drug-induced immune hemolytic anemia (DIIHA) is rare, and a specialized laboratory is often required to provide the optimal serological tests to confirm the diagnosis. The most common drugs associated with DIIHA and the hypotheses for the mechanisms thought to be involved have changed during the last few decades. The drugs most frequently associated with DIIHA at this time are cefotetan, ceftriaxone, and piperacillin. DIIHA is attributed most commonly to drug-dependent antibodies that can only be detected in the presence of drug (eg, cephalosporin antibodies). DIIHA can also be associated with drug-independent antibodies; such antibodies do not need drug to be present to obtain in vitro reactions (eg, fludarabine). In these latter cases, the drug affects the immune system, causing production of red cell (RBC) autoantibodies; the clinical and laboratory findings are identical to autoimmune hemolytic anemia (AIHA), other than the remission associated with discontinuing the drug. Some of the mechanisms involved in DIIHA are controversial. The most acceptable one involves drugs, like penicillin, that covalently bind to proteins (eg, RBC membrane proteins); RBCs become coated with drug in vivo and, a drug antibody (usually IgG) attaches to the drug-coated RBCs that are subsequently cleared by macrophages. The most controversial is the so-called immune complex mechanism, which has been revised to suggest that most drugs are capable of binding to RBC membrane proteins, but not covalently like penicillins. The combined membrane plus drug can create an immunogen; the antibodies formed can be IgM or IgG and often activate complement, leading to acute intravascular lysis and sometimes renal failure; fatalities are more common in this group. It is still unknown why and how some drugs induce RBC autoantibodies, sometimes causing AIHA.

ABO, D blood typing and subtyping using plug-based microfluidics

A plug-based microfluidic approach was used to perform multiple agglutination assays in parallel without cross-contamination and using only microliter volumes of blood. To perform agglutination assays on-chip, a microfluidic device was designed to combine aqueous streams of antibody, buffer, and red blood cells (RBCs) to form droplets 30-40 nL in volume surrounded by a fluorinated carrier fluid. Using this approach, proof-of-concept ABO and D (Rh) blood typing and group A subtyping were successfully performed by screening against multiple antigens without cross-contamination. On-chip subtyping distinguished common A1 and A2 RBCs by using a lectin-based dilution assay. This flexible platform was extended to differentiate rare, weakly agglutinating RBCs of A subtypes by analyzing agglutination avidity as a function of shear rate. Quantitative analysis of changes in contrast within plugs revealed subtleties in agglutination kinetics and enabled characterization of agglutination of rare blood subtypes. Finally, this platform was used to detect bacteria, demonstrating the potential usefulness of this assay in detecting sepsis and the potential for applications in agglutination-based viral detection. The speed, control, and minimal sample consumption provided by this technology present an advance for point of care applications, blood typing of newborns, and general blood assays in small model organisms.

[Influence of pH values on the agglutinating capacity of anti-A-monoclonal antibodies and their inhibition of A-glucoconjugates of the lipid and protein nature with various isoelectric properties]

The effect caused by medium acidification up to pH 6.5 on the agglutinating ability of 7 anti-A MAbs (2-8, 2-17, 2-19, 2-22, 2-23, 2-28 from Workshop IV and BRIC-145) and their inhibition by glycoconjugates obtained from the membranes of A1 erythrocytes by enzymatic treatment and the chloroform-methanol method, followed by ion-exchange gel chromatography, was evaluated. Medium acidification most significantly reduced the agglutination of A1 erythrocytes in IgM MAbs 2-17 , 2-19, 2-22, and 2-28 and had a weaker manifestation in more alkaline IgM MAbs 2-8, 2-23, and BRIC-145. The inhibition of the lipid isotypes A(1p-00), A(1p-0), and A(1p-3) (with the isoionic pH points of 8.1, 8.0, and 6.55) and the protein ones A(pr-1), and A(pr-3) (with the isoionic pH points of 7.15 and 6.45) was assessed in scores. Acidification up to a pH value of 6.5 in MAbs 2-28 and 2-17 caused a considerable reduction in inhibition with acid A(1p-3) and A(pr-3) with slightly increased inhibition with alkaline A(1p-00); MAbs 2-22 and 2-19 insignificantly and selectively altered the inhibitory capacity by more alkaline types of glycoconjugates; MAb 2-8 hardly changed inhibition. All the above illustrates a significant part played in the study effect by both the charge of glycotopes and antibodies and specificity--the selective avidity of MAbs to certain isotypes of A glycotopes.

Red blood cell membrane-bound IgG: demonstration of antibodies in patients with autoimmune haemolytic anaemia and immune complexes in patients with rheumatic diseases

Immunoglobulin G (IgG) bound in vivo to the surfaces of red blood cells (RBC-IgG) was quantificated by an enzyme-linked immunosorbent assay (ELISA) using the cells themselves as solid phase. The method was applied on RBC from normal subjects, patients with autoimmune haemolytic anaemia (AIHA) and rheumatoid patients with and without circulating immune complexes (CIC). Small amounts of RBC-IgG were detected in normal subjects and rheumatoid patients without CIC. Fifteen out of 16 patients with AIHA had increased RBC-IgG indicating RBC sensitization with IgG antibodies, although only eight patients had a positive direct antiglobulin test (DAT) with anti-IgG. Ten out of 13 rheumatoid patients with a negative DAT and with CIC had increased RBC-IgG suggesting RBC C3 receptor-bound IC. The results provide background for further studies of the significance of RBC-IgG in health and disease.

Influence of the spleen on the expression of surface antigens on parasitized erythrocytes

Two malaria parasites, Plasmodium knowlesi and P. falciparum, when passaged in splenectomized hosts alter or fail to express parasite-dependent antigens on the surface membrane of erythrocytes infected with mature parasites. Experiments with cloned populations of P.knowlesi show this change to be phenotypic and to be modulated by the spleen of the host. In addition, the induction of antigen variation in P. knowlesi malaria apparently requires two factors: specific antibody and the spleen. Along with the altered expression of P. knowlesi variant antigen on the infected erythrocyte surface, there is a decrease in parasite virulence in non-splenectomized monkeys. It is suggested that the spleen-dependent expression of malarial antigens on the parasitized erythrocyte may be an adaptation of the malaria parasite for survival in the presence of a potentially destructive spleen-mediated host immunity.

[The substantination of isotypical differentiation in AB0 system against nonagglutinogenic acid glycotopes of lipid origin]

Monoclonal reagents from Workshop IV were inhibited by glucoconjugates obtained from the membranes of 3 samples of AB (erythrocytes of different isotypes) by enzymatic treatment and the chloroform-methanol method and tested both serologically and in cell electrophoresis by a change of electrophoretic motility under the influence of antibodies and the complement. Glycoconjugates of the lipid and protein origin were additionally subjected to separation by the ion-exchange column chromatography on fractions of the alkaline and acid types. The differences developed in the inhibiting ability of the acid fractions of A and B antigens. The activity of glycoprotein fraction Apr-3 correlating with the difference in the agglutianability of A1 and A2. For glycolipid A1p-3, on the contrary, it turned out to be more expressed in A2B than in A1B, and it correspondent to electrophoretically revealed differences (A(c'+) in A2B and A(c'-) in A1B). In an A2B donor (A(c'-) B(c'-)) this dependens developed too. The antigenic differences of A and B glycotopes depending upon their origin (protein or lipid) and isoelectric properties are not cofined to erythrocyte agglutinogenity and should be taken into account it the system of isotypical differentiation of AB0.

Transfusion therapy for autoimmune hemolytic anemia patients: a laboratory perspective

Patients presenting with autoimmune hemolytic anemias create inherent challenges to those tasked with providing compatible blood for transfusion therapy. These patients have developed autoantibodies against their own red cell surface antigens. Because these antigens are usually high-incidence, these patients will typically demonstrate panagglutination when their serum is exposed to most commercially procured screening red blood cells. This makes the identification of clinically significant alloantibodies difficult for laboratory personnel. Transfusion history, patient phenotype availability, and previous antibody records all impact the testing methods. The end goal is to identify clinically significant alloantibodies in order to provide antigen negative, compatible red blood cells, which reduces the risk of transfusion related reactions. It is imperative to understand the laboratory results and the techniques available that guide the investigative process.

Evidence for a relationship between bovine erythrocyte lipid membrane peculiarities and immune pressure from ruminal ciliates

Erythrocytes of bovines and other ruminants have a strikingly anomalous phospholipid composition, with low or absent phosphatidylcholine (PC) together with high sphingomyelin (SM) content. Here, we report the presence in normal bovine serum of high levels of anti-phospholipid antibodies of IgM isotype against, PC and the phosphono analogue of phosphatidylethanolamine, aminoethylphosphonolipid (AEPL), normally produced by rumen ciliates. In contrast, no antibodies were detected against SM or N-acyl-phosphatidylethanolamine (NAPE), the major components of bovine erythrocytes. In addition, we found that exposure of the ciliate Tetrahymena thermophila to bovine serum results in rapid lysis, an effect that was inhibited by adsorption of the serum with SM/AEPL liposomes. Furthermore, incubation with bovine serum had a similar effect on freshly obtained ruminal ciliates, and the lytic activity was eliminated by pre-adsorption of the serum with SM/PE liposomes. The ruminant mode of life with its concomitant ciliate fauna is hereby linked to the peculiar conformation of bovine erythrocyte membranes. We propose that the unique phospholipid composition of bovine erythrocytes appears as an evolutionary adaptation to tolerate the lytic effects of anti-phospholipid antibodies generated against AEPL, a membrane component of the huge mass of ruminal ciliates, necessary commensals of this group of mammals.

Inulin sugar glasses preserve the structural integrity and biological activity of influenza virosomes during freeze-drying and storage

Influenza virosomes are reconstituted influenza virus envelopes that may be used as vaccines or as carrier systems for cellular delivery of therapeutic molecules. Here we present a procedure to generate influenza virosomes as a stable dry-powder formulation by freeze-drying (lyophilization) using an amorphous inulin matrix as a stabilizer. In the presence of inulin the structural integrity and fusogenic activity of virosomes were fully preserved during freeze-drying. For example, the immunological properties of the virosomes, i.e. the HA potency in vitro and the immunogenic potential in vivo, were maintained during lyophilization in the presence of inulin. In addition, compared to virosomes dispersed in buffer, inulin-formulated virosomes showed substantially prolonged preservation of the HA potency upon storage. Also the capacity of virosomes to mediate cellular delivery of macromolecules was maintained during lyophilization in the presence of inulin and upon subsequent storage. Specifically, when dispersed in buffer, virosomes with encapsulated plasmid DNA lost their transfection activity completely within 6 weeks, whereas their transfection activity was fully preserved for at least 12 weeks after incorporation in an inulin matrix. Thus, in the presence of inulin as a stabilizing agent, the shelf-life of influenza virosomes with and without encapsulated macromolecules was considerably prolonged. Formulation of influenza virosomes as a dry-powder is advantageous for storage and transport and offers the possibility to develop needle-free dosage forms, e.g. for oral, nasal, pulmonal, or dermal delivery.

Cross-reactivity of anti-H pylori antibodies with membrane antigens of human erythrocytes

AIM: To investigate whether anti-H pylori antibodies have cross-reaction with antigens of erythrocyte membrane.

METHODS: Blood samples were collected from 14 volunteers (8 positive and 6 negative for H pylori detected by ¹³C-urea breath test) of the general population. Erythrocyte membrane proteins of the subjects were examined by Western blot using anti-H pylori serum. The proteins related to the positive bands were identified by mass spectrum analysis.

RESULTS: Anti-H pylori antibodies had cross-reaction with the proteins of about 50 kDa of erythrocyte membranes in all samples independent of H pylori infection. One protein in the positive band was identified as Chain S, the crystal structure of the cytoplasmic domain of human erythrocyte Band-3 protein.

CONCLUSION: Anti-H pylori antibodies cross-react with some antigens of human erythrocyte membrane, which may provide a clue for the relationship between H pylori infection and vascular disorders.

Intratumoral injection of alpha-gal glycolipids induces xenograft-like destruction and conversion of lesions into endogenous vaccines

This study describes a novel cancer immunotherapy treatment that exploits the natural anti-Gal Ab to destroy tumor lesions and convert them into an endogenous vaccine targeted to APC via FcgammaR. Anti-Gal constitutes 1% of immunoglobulins in humans and interacts specifically with alpha-gal epitopes (Galalpha1-3Galbeta1-4GlcNAc-R). The binding of anti-Gal to alpha-gal epitopes on pig cells mediates xenograft rejection. The proposed method uses glycolipid micelles with multiple alpha-gal epitopes (alpha-gal glycolipids). These glycolipids are extracted from rabbit red cell membranes and are comprised of ceramides with carbohydrate chains containing 5-25 carbohydrates, all capped with alpha-gal epitopes. Efficacy of this treatment was demonstrated in alpha1,3-galactosyltransferase knockout mice producing anti-Gal and bearing B16 melanoma or B16/OVA producing OVA as a surrogate tumor Ag. These mice are unique among nonprimate mammals in that, similar to humans, they lack alpha-gal epitopes and can produce the anti-Gal Ab. Intratumoral injection of alpha-gal glycolipids results in local inflammation mediated by anti-Gal binding to the multiple alpha-gal epitopes and activation of complement. These glycolipids spontaneously insert into tumor cell membranes. The binding of anti-Gal to alpha-gal expressing tumor cells induces the destruction of treated lesions as in anti-Gal-mediated xenograft rejection. Anti-Gal further opsonizes tumor cells within the lesion and, thus, targets them for effective uptake by APC that transport the tumor Ags to draining lymph nodes. APC further cross-present immunogenic tumor Ag peptides and elicit a systemic anti-tumor immune response. Similar intratumoral injection of alpha-gal glycolipids in humans is likely to induce the destruction of treated lesions and elicit a protective immune response against micrometastases.

Immunoadsorption of Alloantibodies onto Erythroid Membrane Antigens Encapsulated into Polymeric Microparticles

PURPOSE

Classical immunoadsorbents used for the removal of deleterious molecules in blood such as auto-antibodies are prepared by covalent coupling of antigens onto previously chemically activated supports. Such a chemical treatment may induce a potential toxicity which can be reduced if new immunoadsorbents are prepared by encapsulating erythrocytes-ghosts carrying antigens inside polymeric and porous microparticles.

MATERIALS AND METHODS

Erythrocyte-ghosts obtained by hemolysis in hypotonic buffer were encapsulated into ethylcellulose microparticles by w/o/w emulsification. The porosity of microparticles was evaluated by mercury porosimetry. The adsorption ability of encapsulated antigens was evaluated by hemagglutination after contact in tube or elution in column with polyclonal antibody solutions or human blood-plasma.

RESULTS

The encapsulation process did not significantly alter the evaluated antigens since a significant decrease in anti-A (from 256 to 4) as well as anti-Kell (from 64 to 2) antibody titer has been observed in column after eight chromatographic runs (2 h). The higher the ghost concentration (total protein content of 6 mg/ml), the higher the adsorption capacity.

CONCLUSION

Encapsulation, currently used for drug delivery purposes, may consequently also be applied to the design of new immunoadsorbents as biomaterials.

Complement activation in experimental human malaria infection

The objective of this study was to investigate complement activation in uncomplicated, early phases of human malaria. Fifteen healthy volunteers were experimentally infected with Plasmodium falciparum malaria. Parasitemia and complement activation products were assessed. During blood stage parasitemia, volunteers showed a significant increase in soluble terminal complement complex (TCC) formation. After start of a curative regimen of artemether/lumefantrine, TCC further increased due to activation of both the classical and the alternative pathway. In-vitro studies confirmed activation of complement by parasite cultures. We thus detected an increase in complement activation in volunteers with experimentally induced malaria, even before parasitemia could be detected microscopically. This significant increase in complement activation occurred despite the possible control of TCC formation by complement regulatory proteins on erythrocytes and the extremely low levels of parasitemia. Treatment with artemether/lumefantrine was followed by classical and alternative pathway complement activation, without evidence for mannan-binding-lectin-mediated complement activation.

Conjugation of methoxypolyethylene glycol to the surface of bovine red blood cells

Methoxypolyethylene glycol (mPEG) covalently bound to the surface of human red blood cells (hRBCs) has been shown to decrease immunological recognition of hRBC surface antigens (Bradley et al., 2002). However, there is an increasing shortage of hRBC donations, thus making hRBCs scarce and expensive (Davey, 2004; Riess, 2001). The goal of this study is to similarly PEGylate the surface of bovine RBCs (bRBCs) with the aim of reducing the demand on human blood donations needed for blood transfusions. This study investigates the feasibility of modifying the surface of bRBCs with the succinimidyl ester of methoxypolyethylene glycol propionic acid (SPA-mPEG) for use as a potential blood substitute. The oxygen binding affinity of PEGylated bRBCs was moderately increased with increasing initial SPA-mPEG concentrations up to 4 mM when reacted with bRBCs at a hematocrit of 12%. Oxygen transport simulations verified that SPA-mPEG conjugated bRBCs could still transport oxygen to pancreatic islet tissues even under extreme conditions. PEGylated bRBCs reconstituted to a hematocrit of 40% exhibited viscosities on the order of approximately 3 cp, similar to hRBCs at the same hematocrit. Taken together, the results of this study demonstrate the success of PEGylating bRBCs to yield modified cells with oxygen binding, transport and flow properties similar to that of hRBCs.

Sphingomyelinases D induce direct association of C1q to the erythrocyte membrane causing complement mediated autologous haemolysis

Bites by Loxosceles spiders can induce severe clinical symptoms, including dermonecrosis, thrombosis, vascular leakage, haemolysis and persistent inflammation. The causative toxin is a sphingomyelinase D (SMase D) that cleaves sphingomyelin into choline and ceramide-1-phosphate. A similar enzyme, showing comparable bioactivity, is secreted by certain pathogenic corynebacteria and acts as a potent virulence factor. We have previously found that SMase D toxins led to an increased susceptibility of human erythrocytes (E) to activation of complement (C) via the classical pathway (CP) in the absence of antibodies. In the present study we have investigated the CP initiating components involved in the haemolysis induced by SMases from Corynebacterium pseudotuberculosis (PLD) and from Loxosceles intermedia venom (P1). When P1 or PLD treated E were incubated with C8-depleted human serum, an increase in C1q, serum amyloid protein (SAP) and C-reactive protein (CRP) binding was observed. While purified C1q, SAP and CRP were found to bind to P1 or PLD treated E, depletion of SAP or CRP from human serum did not prevent C-mediated lysis, suggesting that pentraxins are not involved in the initiation of C-activation. However depletion of C1 lead to a greatly reduced haemolysis, demonstrating that the activation of the CP is caused by direct binding of C1q to the SMase treated cells. Binding of fluid phase C-regulators C4b-binding protein and factor H was also observed, however these C-regulators in conjunction with the membrane bound C-regulators were unable to prevent haemolysis, demonstrating the potency of SMase D facilitated binding of C1 and activation of C.

An alloantibody to a high-prevalence MNS antigen in a person with a GP.JL/Mk phenotype

The low-prevalence MNS blood group antigenTSEN is located at the junction of glycophorin A (GPA) to glycophorin B (GPB) in several hybrid glycophorin molecules. Extremely rare people have RBCs with a double dose of the TSEN antigen and have made an antibody to a high-prevalence MNS antigen. We report the first patient who is heterozygous for GYP.JL and Mk. During prenatal tests,an alloantibody to a high-prevalence antigen was detected in the serum of a 21-year-old Hispanic woman. The antibody detected an antigen resistant to treatment by papain, trypsin, alpha-chymotrypsin, or DTT. The antibody was strongly reactive by the IAT with all RBCs tested except those having the MkMk, GP.Hil/GP.Hil, or GP.JL/GP.JL phenotypes. The patient's RBCs typed M+N-S+/-s-U+, En(a+/-), Hut-, Mi(a-), Mur-, Vw-, Wr(a-b-), and were TSEN+, MINY+. Reactivity with Glycine soja suggested that her RBCs had a decreased level of sialic acid. Immunoblotting showed the presence of monomer and dimer forms of a GP(A-B) hybrid and an absence of GPA and GPB. Sequencing of DNA and PCR-RFLP using the restriction enzyme RsaI confirmed the presence of a hybrid GYP(AB). The patient's antibody was determined to be anti-EnaFR. She is the first person reported with the GP.JL phenotype associated with a deletion of GYPA and GYPB in trans to GYP.JL.

Critical role of the C-terminal domains of factor H in regulating complement activation at cell surfaces

The plasma protein factor H primarily controls the activation of the alternative pathway of complement. The C-terminal of factor H is known to be involved in protection of host cells from complement attack. In the present study, we show that domains 19-20 alone are capable of discriminating between host-like and complement-activating cells. Furthermore, although factor H possesses three binding sites for C3b, binding to cell-bound C3b can be almost completely inhibited by the single site located in domains 19-20. All of the regulatory activities of factor H are expressed by the N-terminal four domains, but these activities toward cell-bound C3b are inhibited by isolated recombinant domains 19-20 (rH 19-20). Direct competition with the N-terminal site is unlikely to explain this because regulation of fluid phase C3b is unaffected by domains 19-20. Finally, we show that addition of isolated rH 19-20 to normal human serum leads to aggressive complement-mediated lysis of normally nonactivating sheep erythrocytes and moderate lysis of human erythrocytes, which possess membrane-bound regulators of complement. Taken together, the results highlight the importance of the cell surface protective functions exhibited by factor H compared with other complement regulatory proteins. The results may also explain why atypical hemolytic uremic syndrome patients with mutations affecting domains 19-20 can maintain complement homeostasis in plasma while their complement system attacks erythrocytes, platelets, endothelial cells, and kidney tissue.

Non-opsonising aggregates of IgG and complement in haemoglobin C erythrocytes

Haemoglobin C (HbC) differs from normal HbA by a lysine for glutamate substitution at position 6 of beta-globin. Heterozygous AC and homozygous CC phenotypes are associated with shortened erythrocyte life spans and mild anaemia. AC and CC erythrocytes contain elevated amounts of membrane-associated haemichromes, band 3 clusters, and immunoglobulin G (IgG) in vivo. These findings led us to investigate whether AC and CC erythrocytes might expose elevated levels of IgG and complement, two opsonins that have been implicated in the phagocytic clearance of senescent and sickle erythrocytes. Surprisingly, we found IgG, complement, and other plasma proteins co-localised in aggregates beneath the membrane of circulating AC and CC erythrocytes. These observations, and our finding of similar aggregates in erythrocytes heterozygous or homozygous for haemoglobin S (sickle-cell haemoglobin), suggest that the vast majority of membrane-associated IgG and complement detected in these abnormal erythrocytes is intracellular and does not contribute to the eventual opsonic clearance of these cells. Phagocytosis studies with macrophages provide evidence in support of this suggestion. Studies of erythrocyte clearance that involve the detection of membrane-associated IgG and complement as putative opsonins should investigate the possibility that these plasma proteins reside in the erythrocyte interior, and not on the cell surface.

The effects of marathon running on expression of the complement regulatory proteins CD55 (DAF) and CD59 (MACIF) on red blood cells

Exercise is known to result in the haemolysis of red blood cells (RBCs). Although mechanical stressors such as footstrike and an increased velocity of blood flow may be involved, the biological mechanisms that underpin RBC haemolysis remain elusive. RBCs are potentially susceptible to lysis by autologous complement activation. RBCs are protected from the lytic effects of complement by regulatory proteins (CRPs) bound to the cell membrane via glycosylphosphatidylinositol (GPI) anchors. This study aimed to determine if marathon running would result in RBC haemolysis through a loss of membrane expression of the CRPs CD55 (decay accelerating factor) and CD59 (membrane attack complex inhibitory factor). Blood samples were obtained from 14 male runners before, within 30 min after, and 24 h after completion of the 2004 London Marathon. RBCs were assessed for cell surface CD55 and CD59 expression using indirect immunofluorescence assays and flow cytometry. No significant changes in the total RBC count, haematocrit or haemoglobin concentrations were found in response to running the marathon (P > 0.05). Blood bilirubin concentrations after the marathon were significantly greater than the pre-race values (P < 0.01). The relative fluorescent intensity (arbitrary units) of CD55 and CD59 expression on RBC membranes did not change in response to the marathon race (P > 0.05). In conclusion, marathon running did not alter the expression of CD55 or CD59 on RBCs, despite concomitant elevations in blood bilirubin concentrations. Consequently, any haemolysis of RBCs that occurred in response to the marathon was not likely due to a loss of membrane bound CRPs and subsequent cell lysis by autologous complement.

Generation of cross-protective antibodies against Plasmodium falciparum sequestration by immunization with an erythrocyte membrane protein 1-duffy binding-like 1 alpha domain

The Plasmodium falciparum erythrocyte membrane protein 1 (PfEMP1) is an important virulence factor on the surface of infected erythrocytes. Naturally acquired antibodies to PfEMP1 expressed by parasites causing severe malaria are suggested to be protective and of major interest for the development of a vaccine against severe disease. In this study, the PfEMP1 expressed by a parasite clone displaying a multiadhesive phenotype associated with severe malaria was well recognized by sera of malaria semi-immune children. The efficiency of the Duffy binding-like 1 alpha (DBL1 alpha) domain of this PfEMP1 was therefore, alone or in combination with two additional DBL1 alpha domains, evaluated as a potential vaccine candidate using both a rodent model and a primate model. Antibodies against the DBL1 alpha domain were generated by immunization with recombinant DBL1 alpha-Semliki Forest virus particles and recombinant protein and analyzed in vitro. The immunized animals were challenged in vivo with various parasite strains or clones. Immunization with the PfEMP1-DBL1 alpha domain abolished the PfEMP1-dependent sequestration of the homologous strain in immunized rats and substantially inhibited parasite adhesion in immunized monkeys. Protection against sequestration of heterologous parasite strains was also confirmed by direct or indirect challenge in the rat model. These results strongly support the use of the DBL1 alpha domain in the development of a vaccine targeting severe malaria.

Case report and literature review: transient Inab phenotype and an agglutinating anti-IFC in a patient with a gastrointestinal problem

BACKGROUND

The Inab phenotype is a rare deficiency of all Cromer antigens. These antigens are carried on the decay-accelerating factor (DAF, CD55) molecule that is attached to the red blood cell (RBC) membrane by a glycosylphosphatidylinositol (GPI) anchor. Although typically inherited, an acquired and transient form of the Inab phenotype also exists. A patient with the triad of transient Inab phenotype, a direct-agglutinating anti-IFC, and gastrointestinal (GI) abnormalities is reported.

CASE REPORT

An 18-month-old boy with gastroesophageal reflux disease requiring a feeding tube, milk and soy intolerance, and severe growth retardation, as well as vision and hearing deficits from cytomegalovirus infection, was identified when pretransfusion testing revealed a potent panagglutinin (titer > 2000 at 4 degrees C). This antibody did not react with Dr(a-) and IFC RBCs, and the autocontrol was negative. The patient's RBCs lacked CD55 by flow cytometric techniques but had normal levels of CD59 and antigens such as Yt(a) and Emm, carried on GPI-linked proteins, thus excluding paroxysmal nocturnal hemoglobinuria. Several months after initial detection, the anti-IFC was virtually undetectable and his cells reacted weakly with anti-IFC, anti-Dr(a), and anti-CD55. RBCs from the propositus' parents and brother demonstrated normal CD55 and CD59 expression.

CONCLUSION

This is the first example of a direct-agglutinating anti-IFC. The cause of the transient depression in CD55 protein (and thus Cromer system antigens) and appearance of anti-IFC remains unknown, as does the relationship between the patient's GI system abnormalities and these serologic findings.

[Rh antigen stability of mPEG modified red blood cells]

The objective of study was to investigate the Rh antigen stability of mPEG-modified RBC. RBC membrane protein SDS-PAGE technology was used to analyze the combination of the mPEG modified RBC membrane protein with mPEG molecules; the RBC ghost coagulation test and 4 degrees C CPD-preserved modified RBC mixed with matched blood were used to observe the stability of RBC Rh antigen camouflaged by mPEG. The results showed that the blood groups of stored mPEG-modified RBC were kept consistency before or after simulating transfusion, i.e. mixture of modified RBC with matched bloods, while the plasma hemoglobin after simulating transfusion was not only within the normal range during the storage, but also less than that before simulating transfusion even after incubation at 37 degrees C. The electrophoresis pattern stained with iodine and Coomassie blue displayed the bands of mPEG combined with RBC membrane protein and the slow mobility of membrane protein. The hemagglutination of PEGylation RBC ghosts did not take place and mPEG still covered the antigen. In conclusion, mPEG-SPA can bind the erythrocyte with its extracted membrane protein in both ghosts and living erythrocytes.

Effect of membrane-bound IgG and desialysation in the interaction of monocytes with senescent erythrocytes

Determination of the erythrocyte lifespan is a complex process affected by many cellular parameters. In the present study we measured and characterised the red blood cell (RBC) membrane proteins, mainly band 3, and quantified membrane-bound IgG in senescent RBC (SeRBC) and young RBC (YRBC). We also investigated, through a functional assay, the interaction between SeRBC and peripheral blood monocytes. We applied this erythrophagocytosis assay to study the phagocytosis of desialysed RBC. The results obtained showed no changes in the protein content between SeRBC and YRBC and no differences when examining membrane proteins by SDS-PAGE. Then, considering that the accumulation of autologous IgG on RBC membrane provides a direct mechanism for the removal of SeRBC, we measured the IgG content of intact RBC using an enzyme-linked anti-immunoglobulin test finding that the number of IgG molecules bound to SeRBC was significantly higher than that observed for YRBC. The increase observed in the percentage of erythrophagocytosis with SeRBC and sensitised RBC (SRBC) confirmed the involvement of autologous IgG in the selective removal of erythrocytes. We also observed a higher percentage of monocytes with phagocytosed and adherent RBC (AM) obtained with neuraminidase-treated RBC than those obtained with YRBC. This finding suggests that a decrease in sialic acid content of SeRBC may be involved in physiological erythrophagocytosis.

Anti-erythrocyte natural antibody activity in the unconventional ‘heavy chain’ immunoglobulins of Indian desert camel (Camelus dromedarius)

Members of the family Camelidae contain unconventional 'heavy chain' antibodies (HCAbs) that are devoid of light chains (LCs) in their structure and occur under physiological conditions. The spectrum of antigenic specificities in HCAbs and hence their biological significance is not known at present. Recent studies have however indicated that they contribute significantly towards the immunoglobulin (Ig) receptor diversity. The present study was planned to investigate the natural antibody (NAb) activity in camel HCAbs as further indication of the wide spectrum of their antigenic specificities. Detection of NAbs in the sera and isolated HCAbs of Indian Thar desert camels was undertaken against erythrocyte antigens (E-Ags) from eleven animal species including nine mammals, chicken and frog by using direct haemagglutination (HA) and indirect Coombs' test. HCAbs were found to behave as 'incomplete antibodies' and agglutinated erythrocytes of different animal species in indirect Coombs' test using rabbit anti-camel IgG3 (HCAbs) antiserum. Variations were noticed in the Coombs' titres against erythrocytes from different species. HCAbs also reacted against E-Ags in immunoblots. These findings provide further evidence that camelid HCAbs are produced against diverse antigens (Ags) under natural conditions, thereby contributing to camelid Ig receptor diversity.

A simple method for quantifying high density antigens in erythrocyte membrane by flow cytometry

RBC flow cytometric analysis is usually used to quantify antigen content. Calibration systems enable antigen content determination by relating mean fluorescence intensity with the number of bound antibody molecules (equivalent to the number of antigen molecules). For that reason, antibodies must be used at saturating concentration, which may lead to agglutination when working with high density antigens. Then, forward scattering, side scattering and fluorescence will be increased, thus obtaining wrong results. In this work, the simple Langmuir adhesion model was applied. Flow cytometry was used to quantify GPA, a transmembrane protein present at high density on RBC. The fluorescence intensity of samples at different anti-GPA sub-saturating concentrations was measured. Sometimes, agglutinates were present and two peaks of fluorescence were observed, the principal one corresponding to isolated cells and the secondary one corresponding to agglutinated cells. In those cases, the principal peak was taken into account for the analysis. The GPA antigen content obtained for nine analyzed samples ranged from 3 to 13 x 10(5) sites per cell, which is similar to those values found in literature. Therefore, the Langmuir adsorption model enables us to determine the antigen content for the anti-GPA/GPA system on RBC membrane. This model could be used to quantify high density antigens in RBC and in other cells.

[Comparison of modification of surface xenoantigens on bovine and porcine erythrocytes]

This study was aimed to explore impact of removal of cell membrane G alalpha1-3Gal beta1-4Glc NAc epitopes (called alpha-Gal) and chemical modification of other xenoantigen on bovine red blood cell (bRBC) and porcine red blood cell (pRBC) antigenicity and to compare their modified erythrocytes, in order to provide basis for development of human blood substitute with rich source, high safety and efficacy. bRBC and pRBC were subjected to both enzymatic removal of membrane alpha-Gal with recombinant coffee bean alpha-galactosidase (rC alpha-GalE) and covalent attachment of benzotriazole carbonate-linked methoxypolyethylene glycol (mPEG-BTC, MW = 20 kD). The effects of treatment were measured by hemagglutination, flow cytometric assay of IgG binding and clinical cross-match testing to human sera. The results showed that although alpha-galactosidase treatment reduced hemagglutination titers to levels similar to negative control, the combination of the treatments was most effective. Clinically used cross-match tests between bRBC, pRBC and human sera demonstrated increased compatibility. Bovine RBC were more robust than pRBC, and had less xenoantigens, and had longer half life than pRBC in vivo. These characteristics suggested that bRBCs were more suitable to investigation as an alternatives to hRBC in clinical transfusion than pRBC. These data suggested that strategies to remove or mask xenoantigens on bRBC reduce antigenicity sufficiently to allow in vitro cross-match compatibility to human sera, and therefore bRBC following modification may be considered as human blood substitute.

A comprehensive analysis of DEL types: partial DEL individuals are prone to anti-D alloimmunization

BACKGROUND

The D antigen of the polymorphic Rh blood group system is of particular clinical importance regarding transfusion- and pregnancy-induced alloimmunization. Different RhD variants with specific clinical implications have been characterized. The least expressed D variants collectively called DEL are serologically detectable only by adsorption-elution techniques, with so far only poorly defined antigenic properties.

STUDY DESIGN AND METHODS

A comprehensive immunohematologic analysis of five of the six currently known DEL genotypes was performed. DEL phenotypes associated with the RHD(M295I), RHD(IVS3+1g>a), RHD(K409K), RHD(X418L), or RHD(IVS5-38del4) allele were characterized with extended serology and flow cytometry.

RESULTS

Epitope mapping with adsorption-elution revealed a prominent D epitope loss in the RHD(IVS3+1g>a)-associated DEL phenotype, whereas in the other four DEL types no signs of qualitative D antigen alteration were detected. The observation of alloanti-D in two RHD(IVS3+1g>a) cases confirmed the partial nature of this DEL phenotype. The RHD(M295I) phenotype exhibited the highest D antigen expression among all investigated DEL types, as determined by a semiquantitative adsorption-elution approach and flow cytometry.

CONCLUSION

In conclusion, evidence is provided that different DEL genotypes code either for partial or complete D antigen expression and that this finding is clinically relevant.

Weak D type 1.1 exemplifies another complexity in weak D genotyping

BACKGROUND

Weak D expression is caused by a large number of RHD alleles. Increasingly recommendations for D+ or D- transfusions are based on polymerase chain reaction (PCR) identification of certain RHD alleles. Possible sources of error are rare D variants that are inadvertently carrying known polymorphisms of frequent weak D types.

STUDY DESIGN AND METHODS

Weak D donors were checked by direct column agglutination. In donors with unusually weak expression of D, the molecular weak D type was determined by weak D PCR and nucleotide sequencing. The serologic profile of a weak D type 1 variant was determined by agglutination serology and flow cytometry.

RESULTS

Several donors in whom direct agglutination barely revealed any D expression were shown to carry the new RHD(L18V,V270G) allele dubbed weak D type 1.1. Initially, such donors had been mistyped as weak D type 1 by PCR. In a systematic study, weak D type 1.1 was shown to be present in 7 of 23 donors with very weak D expression who all lived in a restricted area of Northern Germany. Although weak D type 1.1 was typed D- or barely D+ by direct agglutination, it was easily detected by antiglobulin technique and was shown to carry about 600 antigens D per red blood cell.

CONCLUSION

The observation of weak D type 1.1 with its distinct phenotype pinpointed to two general problems of current RHD genotyping strategies: Mistyping of alleles with additional mutations and striking geographic variation of the allele distributions.

Novel weak D types 31 and 32: adsorption-elution-supported D antigen analysis and comparison to prevalent weak D types

BACKGROUND

Weak D types are thought to express rather quantitative than qualitative D antigen variants. Distinct type-specific phenotypes and weak D cases with anti-D alloimmunization, however, suggest a variable degree of D antigen alteration.

STUDY DESIGN AND METHODS

Variant D types were investigated by use of molecular typing, RHD sequencing, extended serologic D antigen investigations, and flow cytometric D antigen density determination.

RESULTS

Two novel weak D types were discovered, termed weak D type 31 and 32 with single RHD nucleotide substitutions coding for amino acid exchanges in predicted intracellular RhD polypeptide stretches, with antigen densities of approximately 130 and 50 D sites per red blood cell, respectively. Adsorption-elution technique-supported D epitope mapping of these two weak D types, the recently described weak D type 26, and of the most common Central European weak D types (weak D types 1, 2, 3, 4.0, and 4.1) demonstrated the expression of all tested D epitopes. In contrast, a distinct D epitope loss was detected in weak D type 15 and partial D control samples.

CONCLUSION

All novel and prevalent weak D types expressed all tested D epitopes. Our results indicate that adsorption-elution techniques may be of advantage whenever D epitope loss is suspected in extremely weak D variants.

Storage-related changes in erythrocyte band 3: not a case for the Diego blood group antigens

Removal of erythrocytes from the circulation is mediated by the immune system. Changes in structure and function of band 3, a major membrane protein of the erythrocyte, trigger the binding of antibodies to a band 3-derived neoantigen, senescent cell antigen, on erythrocytes aged in vivo. This mechanism probably is also involved in determining the survival of erythrocytes after transfusion. Band 3 is the carrier of the Diego blood group system, and subtle changes in the three-dimensional conformation of the same extracellular loops of band 3 determine Diego blood group activity as well as senescent cell antigen activity. Therefore we used the Diego blood group system to probe these changes with a combination of serological and immunochemical methods. Our data indicate that changes in band 3 structure during storage under blood bank conditions, as shown by immunoblot analysis, are not detectable as changes in expression of Diego antigens in intact cells. This makes it unlikely that immunological removal of erythrocytes after transfusion is mediated by reactions involving the Diego blood group system.

Band 3 clustering promotes the exposure of neoantigens in Plasmodium falciparum-infected erythrocytes

Erythrocytes infected with the human malaria parasite Plasmodium falciparum become structurally and antigenically modified as a consequence of intracellular parasite development. The new antigens that appear on the surface of the infected erythrocyte originate from parasite-encoded proteins and by modification of the erythrocyte membrane protein band 3. Here, we show that anti-peptide antibodies generated against an amino acid sequence (YETFSKLIKIFQDH) of human band 3, and previously identified as mediating adhesion of infected erythrocytes to CD36, recognized P. falciparum-infected erythrocytes. In addition, sera from individuals living in a malaria endemic area (and who are presumably immune) contained immunoglobulins specific for this region of band 3. The anti-peptide antibodies reacted with the surface excrescences (knobs) on falciparum-infected erythrocytes. In uninfected erythrocytes, the band 3 region was cryptic and its exposure on the falciparum-infected erythrocyte surface required clustering of band 3 protein. Thus, a parasite-induced modification of band 3 promotes adhesion and induces antigenic changes in the P. falciparum-infected erythrocyte.

Investigation of red blood cell antigens with highly fluorescent and stable semiconductor quantum dots

We report a new methodology for red blood cell antigen expression determination by a simple labeling procedure employing luminescent semiconductor quantum dots. Highly luminescent and stable core shell cadmium sulfide/cadmium hydroxide colloidal particles are obtained, with a predominant size of 9 nm. The core-shell quantum dots are functionalized with glutaraldehyde and conjugated to a monoclonal anti-A antibody to target antigen-A in red blood cell membranes. Erythrocyte samples of blood groups A+, A2+, and O+ are used for this purpose. Confocal microscopy images show that after 30 min of conjugation time, type A+ and A2+ erythrocytes present bright emission, whereas the O+ group cells show no emission. Fluorescence intensity maps show different antigen expressions for the distinct erythrocyte types. The results obtained strongly suggest that this simple labeling procedure may be employed as an efficient tool to investigate quantitatively the distribution and expression of antigens in red blood cell membranes.

[Preparation and characterization of non-agglutinating mAbs against membrane antigen on human erythrocytes]

AIM

To prepare monoclonal antibodies (mAbs) against membrane antigens on human erythrocytes and characterize their properties.

METHODS

BALB/c mice were immunized with the membrane antigens of human type O erythrocytes. The splenocytes of the immunized mice were fused with Sp2/0 myeloma cells by hybridoma technique. The antibodies to common antigen on human erythrocytes were screened by hexadimethrine bromide (polybrene) test tube method and then the agglutinating antibodies (complete antibodies) were weeded out by slide hemagglutination assay. The hybridoma cells secreting non-agglutinating antibodies (incomplete antibodies) were cloned by limiting dilution method. The stability of the obtained hybridoma cells and the properties of the mAbs were identified.

RESULTS

One hybridoma cell 2E8 was obtained, which secreted non-agglutinating antibody. The mAb 2E8 belonged to IgG1, could agglutinate H antigen, and had no species cross-agglutination reaction. The titers of culture supernatant and ascites of 2E8 were 1:1,024 and 1:64x10(6), respectively. When the affinity of mAb 2E8 was evaluated by agglutination reaction, erythrocytes began to agglutinate after 7 seconds and the clots exceeded 1 mm(2) in 3 minutes.

CONCLUSION

The non-agglutinating mAb against H antigen was prepared successfully. The mAb 2E8 has good titer, affinity and specificity, which lays the foundation for preparation of bispecific antibodies (BsAb).