Challenges for the maintaining the microbiological safety of the UK blood supply

The supply of blood, blood products and components in the UK, as elsewhere, is safe, although there is no cause for complacency. Use of blood, blood products and components is not without risk of morbidity and mortality. Transfusion-transmitted infections (TTIs) continue to occur and may severely affect the health and welfare of recipients. As indicated by recent and current inquiries, public interest in these TTIs is huge. The risk of TTI can be mitigated but not abolished. Measures to reduce risk include screening of donors, testing of donations and, where appropriate, treatment of donations. The introduction of newer screening tests might identify some infectious donations but come at a cost, which could exceed a justifiable limit. Thus, the recognition, detection, reporting and investigation of cases of possible TTIs need to be improved. Recipients of blood should understand that, although transfusion in the UK is safe, it is not free of risk and so should be provided with full information so that properly informed consent can be given.

Importation of plasma and use of apheresis platelets as risk reduction measures for variant Creutzfeldt-Jakob disease: The SaBTO review

Following recognition that blood, blood components, tissues and organs donated by infected donors could transmit infectious prions causing variant Creutzfeldt-Jakob Disease (vCJD), several risk reduction measures were introduced in the UK. The Advisory Committee on the Safety of Blood, Tissues and Organs (SaBTO) established a working group to review the measures in place. Factors considered included: ethical issues around the current provisions and potential changes; operational issues for blood establishments and hospitals; a review from the Advisory Committee on Dangerous Pathogens (ACDP) showing the downward trend in the estimated number of future cases of vCJD; and cost-effectiveness. The working group recommended that the current vCJD risk reduction measures for individuals born after 1995 or with thrombotic thrombocytopenic purpura (TTP) could be withdrawn. After consultation with stakeholders, SaBTO accepted these proposals which allow more equal provision of components, less operational complexity and risk, and more resources to be deployed elsewhere in the NHS. The potential saving on plasma will be £500 m and moving to using pooled platelets in additive solution for all recipients will bring potential savings of £280 m over the next 50 to 60 years. There could be small number of additional clinical cases of vCJD: 1-2 (<1-14; 95% CI) from plasma and 3-4 (<1 to 45; 95% CI) from platelets. Local and national guidelines will still be applied for managing individual conditions. UK Ministers for Health accepted SaBTO's recommendations on 9 Sept 2019 and implementation began immediately. This paper describes the review and rationale leading to these recommendations.

A prion reduction filter does not completely remove endogenous prion infectivity from sheep blood

BACKGROUND

Variant Creutzfeldt-Jakob disease (vCJD) is a transmissible spongiform encephalopathy affecting humans, acquired initially through infection with bovine spongiform encephalopathy (BSE). A small number of vCJD cases have been acquired through the transfusion of blood from asymptomatic donors who subsequently developed vCJD. Filter devices that selectively bind the infectious agent associated with prion disease have been developed for removal of infection from blood. This study independently assessed one such filter, the P-CAPT filter, for efficacy in removing infectivity associated with the BSE agent in sheep blood. The sheep BSE model has previously been used to evaluate the distribution of infectivity in clinically relevant blood components. This is the first study to assess the ability of the P-CAPT filter to remove endogenous infectivity associated with blood components prepared from a large animal model.

STUDY DESIGN AND METHODS

Paired units of leukoreduced red blood cells (LR-RBCs) were prepared from donors at the clinical stage of infection and confirmed as having BSE. One cohort of recipients was transfused with LR-RBCs alone, whereas a parallel cohort received LR and P-CAPT-filtered RBCs (LR-RBCs-P-CAPT).

RESULTS

Of 14 recipients, two have been confirmed as having BSE. These sheep had received LR-RBCs and LR-RBCs-P-CAPT from the same donor.

CONCLUSIONS

The results indicate that, after leukoreduction and P-CAPT filtration, there can still be sufficient residual infectivity in sheep RBCs to transmit infection when transfused into a susceptible recipient.

Real time quaking-induced conversion analysis of cerebrospinal fluid in sporadic Creutzfeldt-Jakob disease

OBJECTIVE

Current cerebrospinal fluid (CSF) tests for sporadic Creutzfeldt-Jakob disease (sCJD) are based on the detection of surrogate markers of neuronal damage such as CSF 14-3-3, which are not specific for sCJD. A number of prion protein conversion assays have been developed, including real time quaking-induced conversion (RT-QuIC). The objective of this study is to investigate whether CSF RT-QuIC analysis could be used as a diagnostic test in sCJD.

METHODS

An exploratory study was undertaken that analyzed 108 CSF samples from patients with neuropathologically confirmed sCJD or from control patients. Of the 108 CSF samples, 56 were from sCJD patients (30 female, 26 male; aged 31-84 years; mean age, 62.3 ± 13.5 years), and 52 were from control patients (26 female, 26 male; aged 43-84 years; mean age, 67.8 ± 10.4 years). A confirmatory group of 118 patients was subsequently examined that consisted of 67 cases of neuropathologically confirmed sCJD (33 female, 34 male; aged 39-82 years; mean age, 67.5 ± 9.0 years) and 51 control cases (26 female, 25 male; aged 36-87 years; mean age, 63.5 ± 11.6 years).

RESULTS

The exploratory study showed that RT-QuIC analysis had a sensitivity of 91% and a specificity of 98% for the diagnosis of sCJD. These results were confirmed in the confirmatory study, which showed that CSF RT-QuIC analysis had a sensitivity and specificity of 87% and 100%, respectively.

INTERPRETATION

This study shows that CSF RT-QuIC analysis has the potential to be a more specific diagnostic test for sCJD than current CSF tests.

Sensitive and specific detection of sporadic Creutzfeldt-Jakob disease brain prion protein using real-time quaking-induced conversion

Real-time quaking-induced conversion (RT-QuIC) is an assay in which disease-associated prion protein (PrP) initiates a rapid conformational transition in recombinant PrP (recPrP), resulting in the formation of amyloid that can be monitored in real time using the dye thioflavin T. It therefore has potential advantages over analogous cell-free PrP conversion assays such as protein misfolding cyclic amplification (PMCA). The QuIC assay and the related amyloid seeding assay have been developed largely using rodent-passaged sheep scrapie strains. Given the potential RT-QuIC has for Creutzfeldt-Jakob disease (CJD) research and human prion test development, this study characterized the behaviour of a range of CJD brain specimens with hamster and human recPrP in the RT-QuIC assay. The results showed that RT-QuIC is a rapid, sensitive and specific test for the form of abnormal PrP found in the most commonly occurring forms of sporadic CJD. The assay appeared to be largely independent of species-related sequence differences between human and hamster recPrP and of the methionine/valine polymorphism at codon 129 of the human PrP gene. However, with the same conditions and substrate, the assay was less efficient in detecting the abnormal PrP that characterizes variant CJD brain. Comparison of these QuIC results with those previously obtained using PMCA suggested that these two seemingly similar assays differ in important respects.

Prevalence of disease related prion protein in anonymous tonsil specimens in Britain: cross sectional opportunistic survey

OBJECTIVE

To establish with improved accuracy the prevalence of disease related prion protein (PrP(CJD)) in the population of Britain and thereby guide a proportionate public health response to limit the threat of healthcare associated transmission of variant Creutzfeldt-Jakob disease (vCJD).

DESIGN

Cross sectional opportunistic survey. Study samples Anonymised tonsil pairs removed at elective tonsillectomy throughout England and Scotland.

SETTING

National anonymous tissue archive for England and Scotland.

MAIN OUTCOME MEASURE

Presence of PrP(CJD) determined by using two enzyme immunoassays based on different analytical principles, with further investigation by immunohistochemistry or immunoblotting of any samples reactive in either assay.

RESULTS

Testing of 63 007 samples was completed by the end of September 2008. Of these, 12 753 were from the birth cohort in which most vCJD cases have arisen (1961-85) and 19 908 were from the 1986-95 cohort that would have been also exposed to bovine spongiform encephalopathy through infected meat or meat products. None of the samples tested was unequivocally reactive in both enzyme immunoassays. Only two samples were reactive in one or other enzyme immunoassay and equivocal in the other, and nine samples were equivocally reactive in both enzyme immunoassays. Two hundred and seventy six samples were initially reactive in one or other enzyme immunoassay; the repeat reactivity rate was 15% or less, depending on the enzyme immunoassay and cut-off definition. None of the samples (including all the 276 initially reactive in enzyme immunoassay) that were investigated by immunohistochemistry or immunoblotting was positive for the presence of PrP(CJD).

CONCLUSIONS

The observed prevalence of PrP(CJD) in tonsils from the 1961-95 combined birth cohort was 0/32 661 with a 95% confidence interval of 0 to 113 per million. In the 1961-85 cohort, the prevalence of zero with a 95% confidence interval of 0 to 289 per million was lower than, but still consistent with, a previous survey of appendix tissue that showed a prevalence of 292 per million with a 95% confidence interval of 60 to 853 per million. Continuing to archive and test tonsil specimens, especially in older birth cohorts, and other complementary large scale anonymous tissue surveys, particularly of post-mortem tissues, will further refine the calculated prevalence of PrP(CJD).

Different inactivating mutations in the LU genes of three individuals with the Lutheran-null phenotype

BACKGROUND

The null phenotype of the Lutheran blood group system, Lu(null) or Lu(a-b-), is characterized by the lack of all Lutheran system antigens. It can arise from three genetic backgrounds: recessive, dominant, or X-linked. Lu(null) of the recessive type appears to result from homozygosity for an inactive LU gene.

STUDY DESIGN AND METHODS

Three unrelated recessive Lu(null) individuals were assessed by standard serologic tests. All exons of the LU gene were directly sequenced from amplified genomic DNA. The validity of the observed mutations within the LU gene was confirmed by the use of either restriction enzymes or allele-specific primers.

RESULTS

All three individuals had the serologic characteristics of recessive Lu(null). One individual was doubly heterozygous for a nonsense mutation 691C>T in exon 6 (Arg231STOP) and a deletion of LU exons 3 and 4. The other two samples showed homozygous nonsense mutations: one had 711C>A in exon 6 (Cys237STOP) and the other 361C>T in exon 3 (Arg121STOP).

CONCLUSIONS

The results revealed four unique genetic backgrounds from three examples of the rare recessive Lu(null) phenotype, each encoding Lutheran glycoproteins with a disrupted structure.

Phenotypic heterogeneity in inherited prion disease (P102L) is associated with differential propagation of protease-resistant wild-type and mutant prion protein

Inherited prion diseases are caused by PRNP coding mutations and display marked phenotypic heterogeneity within families segregating the same pathogenic mutation. A proline-to-leucine substitution at prion protein (PrP) residue 102 (P102L), classically associated with the Gerstmann-Sträussler-Scheinker (GSS) phenotype, also shows marked clinical and pathological heterogeneity, including patients with a Creutzfeldt-Jakob disease (CJD) phenotype. To date, this heterogeneity has been attributed to temporal and spatial variance in the propagation of distinct protease-resistant (PrP(Sc)) isoforms of mutant PrP. Here, using a monoclonal antibody that recognizes wild-type PrP, but not PrP 102L, we reveal a spectrum of involvement of wild-type PrP(Sc) in P102L individuals. PrP(Sc) isoforms derived from wild-type and mutant PrP are distinct both from each other and from those seen in sporadic and acquired CJD. Such differential propagation of disease-related isoforms of wild-type PrP and PrP 102L provides a molecular mechanism for generation of the multiple clinicopathological phenotypes seen in inherited prion disease.

PrP glycoforms are associated in a strain-specific ratio in native PrPSc

Prion diseases involve conversion of host-encoded cellular prion protein (PrPC) to a disease-related isoform (PrPSc). Using recombinant human beta-PrP, a panel of monoclonal antibodies was produced that efficiently immunoprecipitated native PrPSc and recognized epitopes between residues 93-105, indicating for the first time that this region is exposed in both human vCJD and mouse RML prions. In contrast, monoclonal antibodies raised to human alpha-PrP were more efficient in immunoprecipitating PrPC than PrPSc, and some of them could also distinguish between different PrP glycoforms. Using these monoclonal antibodies, the physical association of PrP glycoforms was studied in normal brain and in the brains of humans and mice with prion disease. It was shown that while PrPC glycoforms can be selectively immunoprecipitated, the differentially glycosylated molecules of native PrPSc are closely associated and always immunoprecipitate together. Furthermore, the ratio of glycoforms comprising immunoprecipitated native PrPSc from diverse prion strains was similar to those observed on denaturing Western blots. These studies are consistent with the view that the proportion of each glycoform incorporated into PrPSc is probably controlled in a strain-specific manner and that each PrPSc particle contains a mixture of glycoforms.

PrPSc binding antibodies are potent inhibitors of prion replication in cell lines

Conversion of the cellular alpha-helical prion protein (PrP(C)) into a disease-associated isoform (PrP(Sc)) is central to the pathogenesis of prion diseases. Molecules targeting either normal or disease-associated isoforms may be of therapeutic interest, and the antibodies binding PrP(C) have been shown to inhibit prion accumulation in vitro. Here we investigate whether antibodies that additionally target disease-associated isoforms such as PrP(Sc) inhibit prion replication in ovine PrP-inducible scrapie-infected Rov cells. We conclude from these experiments that antibodies exclusively binding PrP(C) were relatively inefficient inhibitors of ScRov cell PrP(Sc) accumulation compared with antibodies that additionally targeted disease-associated PrP isoforms. Although the mechanism by which these monoclonal antibodies inhibit prion replication is unclear, some of the data suggest that antibodies might actively increase PrP(Sc) turnover. Thus antibodies that bind to both normal and disease-associated isoforms represent very promising anti-prion agents.

Regional heterogeneity of cellular prion protein isoforms in the mouse brain

Prion diseases are a group of invariably fatal neurodegenerative disorders that include Creutzfeldt-Jakob disease in humans, scrapie in sheep and goats, and bovine spongiform encephalopathy in cattle. The infectious agent or prion is largely composed of an abnormal isoform (PrPSc) of a host encoded normal cellular protein (PrPc). The conversion of PrPc to PrPSc is a dynamic process and, for reasons that are not clear, the distribution of spongiform change and PrPSc deposition varies among prion strains. An obvious explanation for this would be that the transformation efficiency in any given brain region depends on favourable interactions between conformations of PrPc and the prion strain being propagated within it. However, identification of specific PrPc conformations has until now been hampered by a lack of suitable panels of antibodies that discriminate PrPc subspecies under native conditions. In this study, we show that monoclonal antibodies raised against recombinant human prion protein folded into alpha or beta conformations exhibit striking heterogeneity in their specificity for truncations and glycoforms of mouse brain PrPc. We then show that some of these PrPc isoforms are expressed differentially in certain mouse brain regions. This suggests that variation in the expression of PrPc conformations in different brain regions may dictate the pattern of PrPSc deposition and vacuolation, characteristic for different prion strains.

Identification of multiple quantitative trait loci linked to prion disease incubation period in mice

Polymorphisms in the prion protein gene are known to affect prion disease incubation times and susceptibility in humans and mice. However, studies with inbred lines of mice show that large differences in incubation times occur even with the same amino acid sequence of the prion protein, suggesting that other genes may contribute to the observed variation. To identify these loci we analyzed 1,009 animals from an F2 intercross between two strains of mice, CAST/Ei and NZW/OlaHSd, with significantly different incubation periods when challenged with RML scrapie prions. Interval mapping identified three highly significantly linked regions on chromosomes 2, 11, and 12; composite interval mapping suggests that each of these regions includes multiple linked quantitative trait loci. Suggestive evidence for linkage was obtained on chromosomes 6 and 7. The sequence conservation between the mouse and human genome suggests that identification of mouse prion susceptibility alleles may have direct relevance to understanding human susceptibility to bovine spongiform encephalopathy (BSE) infection, as well as identifying key factors in the molecular pathways of prion pathogenesis. However, the demonstration of other major genetic effects on incubation period suggests the need for extreme caution in interpreting estimates of variant Creutzfeldt-Jakob disease epidemic size utilizing existing epidemiological models.

New genotypes in Fy(a-b-) individuals: nonsense mutations (Trp to stop) in the coding sequence of either FY A or FY B

Duffy blood group antigens are carried on a glycoprotein that is predicted to pass through the erythrocyte membrane seven times and is a promiscuous chemokine receptor. The Fy(a- b-) phenotype is present in two-thirds of African-American Blacks but is rare in Caucasians. In Blacks, the phenotype is due to a non-functional GATA-1 motif in the FY B, which silences the gene in erythrocytes but not in other tissues, and these patients do not generally make anti-Fyb or anti-Fy3. We describe here the molecular analysis of FY in three unrelated Caucasians who were studied because they had strong anti-Fy3 in their serum. Each was found to have a point mutation that was predicted to change a tryptophan to a premature stop codon in the coding sequence. In one patient (patient 1), the nonsense mutation was at nucleotide 287 of the major transcript in FY A; in another (patient 2), it was at nucleotide 407 in the major transcript of FY B; and in a third (patient 3), it was at nucleotide 408 of the major transcript of FY A.

The Fy(x) phenotype is associated with a missense mutation in the Fy(b) allele predicting Arg89Cys in the Duffy glycoprotein

The molecular basis of the three major alleles (Fy(a)/Fy(b)/Fy) of the Duffy (FY) blood group system has recently been established but the Fy(x) phenotype associated with weak expression of the Fy(b) and other FY antigens is poorly understood. In the Fy(x) genes of five unrelated British and Swedish donors with the Fy(a+b+weak) phenotype we found two missense mutations predicting amino acid changes Arg89Cys and Ala100Thr in the FY glycoprotein. The same mutations were found in two Fy(a-b+weak) samples from individuals of Swedish and Algerian origin. Their red blood cells showed a marked decrease in Fy(b), Fy3 and Fy6 expression measured by routine serology and flow cytometry. The rare FY genotypes Fy(x)Fy(x) and Fy(x)Fy were confirmed by family studies and DNA sequencing. Screening by allele-specific primer PCR (ASP-PCR) for these mutations among 100 Caucasian and 100 Black random blood donors indicated allele frequencies of 2.5% and 0% respectively. Ala100Thr alone was present in 33% of the Caucasians (but none of the Blacks) with no weakening of FY expression. A novel allele at the FY locus associated with the Fy(x) phenotype was studied. Mistyping of this weak Fy(b) antigen in clinical transfusion medicine may lead to delayed haemolytic transfusion reactions in immunized patients. A potential role for genomic typing is proposed.

Decay-accelerating factor (CD55) deficiency phenotypes in Japanese

Decay-accelerating factor (DAF, CD55) is a complement regulatory glycoprotein that expresses the Cromer-system blood group antigens. Two, very rare, inherited DAF-deficiency phenotypes, Inab and Dr(a-), were identified in Japanese propositi. Red cells of the Inab phenotype propositus had no Cromer-system antigens and did not bind monoclonal anti-DAF. The Inab propositus was homozygous for a DAF non-sense mutation, converting the Trp53 codon to a stop codon; her parents were heterozygous for this mutation. This is the same mutation as that previously found in the original Inab phenotype propositus. Haemagglutination-inhibition titrations of the serum of the Inab propositus with soluble-recombinant DAF demonstrated that anti-IFC represents a mixture of antibodies to all four DAF short consensus repeat domains. The Dr(a-) individual had very low levels of Cromer-system antigens and DAF on her red cells. Loss of a TaqI restriction site from DAF exon 5 suggested that she has a previously detected mutation, encoding a Ser165Leu substitution. Red cells of the two propositi did not show abnormal levels of lysis in an acid lysis test, but after blocking of CD59 with monoclonal antibody, Inab phenotype red cells showed more lysis than Dr(a-) red cells, and Dr(a-) cells showed substantially more lysis than control cells.

Use of domain-deletion mutants to locate Lutheran blood group antigens to each of the five immunoglobulin superfamily domains of the Lutheran glycoprotein: elucidation of the molecular basis of the Lu(a)/Lu(b) and the Au(a)/Au(b) polymorphisms

Lutheran glycoprotein (Lu gp) has five predicted immunoglobulin superfamily (IgSF) domains. K562 cells were transfected with Lu cDNA and tested by flow cytometry with monoclonal antibodies and Lu blood group antisera. The results confirmed the identity of Lu cDNA. Deletion mutants lacking the regions encoding one or more IgSF domains were made by inverse polymerase chain reaction (PCR), expressed in K562 cells, and tested with the same antibodies. The Lu(b) and Lu5 antigens and the epitope recognized by monoclonal antibody BRIC 224 were mapped to the first, N-terminal, IgSF domain. Lu4 and Lu8 were mapped to domain 2; Lu20 to domain 3; Lu7 and BRIC 221 epitope to domain 4, and Lu13 and Au(b) to domain 5. The organization of the LU gene was determined. The region encoding the open reading frame is arranged in 15 exons extending over approximately 11 kb on chromosome 19q13.2. The Lu(a)/Lu(b) and Au(a)/Au(b) blood group polymorphisms were studied using genomic DNA from typed blood donors. The Lu(a) mutation is a base change in exon 3 (G252 to A) encoding an Arg77 (Lu(b)) to His (Lu(a)) change on the CFG face of domain 1. The Au(a)/Au(b) polymorphism is an A1637 to G substitution in exon 12 encoding a Thr539 (Au(a)) to Ala (Au(b)) change on the G strand of domain 5.

Mutations in the erythrocyte chemokine receptor (Duffy) gene: the molecular basis of the Fya/Fyb antigens and identification of a deletion in the Duffy gene of an apparently healthy individual with the Fy(a-b-) phenotype

The erythrocyte chemokine receptor, a receptor for Plasmodium vivax, carries the antigens of the Duffy blood group system. Sequence analysis of reticulocyte RNA from individuals of known Duffy phenotype showed that the Fya antigen differs from the Fyb antigen as a result of a single nucleotide difference (A131 or G) encoding amino acid Gly44 (Fya) or Asp (Fyb) in the N-terminal extracellular domain of the glycoprotein. Evidence is presented for two different genetic backgrounds giving rise to the Fy(a-b-) phenotype. The most likely genetic mechanism in most individuals of the Fy(a-b-) phenotype is down-regulation of Duffy glycoprotein mRNA. However, the Duffy gene from a very rare Caucasian individual (AZ) with the Fy(a-b-) phenotype has a 14 base-pair deletion (nucleotides 287-301) resulting in a frameshift which introduces a stop codon and produces a putative truncated 118 amino acid protein. The occurrence of this mutation in an apparently healthy individual raises questions about the functional importance of the Duffy glycoprotein not only in normal erythrocytes but also in all human cells and tissues.

The Lutheran blood group glycoprotein, another member of the immunoglobulin superfamily, is widely expressed in human tissues and is developmentally regulated in human liver

Glycoproteins expressing the Lutheran blood group antigens were isolated from human erythrocyte membranes and from human fetal liver. Amino acid sequence analyses allowed the design of redundant oligonucleotides that were used to generate a 459-bp, sequence-specific probe by PCR. A cDNA clone of 2400 bp was isolated from a human placental lambda gt 11 library and sequenced, and the deduced amino acid sequence was studied. The predicted mature protein is a type I membrane protein of 597 amino acids with five potential N-glycosylation sites. There are five disulfide-bonded, extracellular, immunoglobulin superfamily domains (two variable-region set and three constant-region set), a single hydrophobic, membrane-spanning domain, and a cytoplasmic domain of 59 residues. The overall structure is similar to that of the human tumor marker MUC 18 and the chicken neural adhesion molecule SC1. The extracellular domains and cytoplasmic domain contain consensus motifs for the binding of integrin and Src homology 3 domains, respectively, suggesting possible receptor and signal-transduction function. Immunostaining of human tissues demonstrated a wide distribution and provided evidence that the glycoprotein is under developmental control in liver and may also be regulated during differentiation in other tissues.

Molecular basis of reduced or absent expression of decay-accelerating factor in Cromer blood group phenotypes

The human erythrocyte blood group system Cromer consists of high-incidence and low-incidence antigens that reside on decay-accelerating factor (DAF; CD55), a glycosyl-phosphatidylinositol-anchored membrane protein that regulates complement activation on cell surfaces. In the Cromer phenotypes Dr(a-) and Inab there is reduced or absent expression of DAF, respectively. This study investigated the molecular basis of the reduced DAF expression by polymerase chain reaction amplification of genomic DNA and RNA/cDNA obtained from Epstein-Barr virus-transformed lymphoblastoid cell lines. Sequence analysis of the Inab propositus showed a single nucleotide substitution in exon 2 of the DAF gene and at the corresponding position in the cDNA, G314-->A resulting in Trp53-->Stop. This truncation near the amino terminus explains the complete absence of surface DAF in the Inab phenotype. A similar analysis was performed for two Dr(a-) individuals, including KZ, who was previously reported to be Inab phenotype but is now shown by immunochemical and serologic methods to be Dr(a-) phenotype. A single nucleotide change was found in exon 5 of the DAF gene, C649-->T resulting in Ser165-->Leu, which we had previously shown to lead to loss of the Dra epitope. However, two species of cDNA were found, one encoding full-length DAF with the single amino acid change and the more abundant species having a 44-nucleotide deletion. The 44 nucleotide deletion includes the single polymorphic site, which creates a cryptic branch point in the Dr(a-) allele that leads to use of a downstream cryptic acceptor splice site. This shifts the reading frame and leads to a premature stop codon that precludes membrane anchoring. Thus, the single point mutation in the Dr(a-) phenotype results in a novel use of alternative splicing and provides a molecular explanation for both the antigenicity and the reduced DAF expression seen in this phenotype.

A point mutation in the GYPC gene results in the expression of the blood group Ana antigen on glycophorin D but not on glycophorin C: further evidence that glycophorin D is a product of the GYPC gene

Glycophorin C (GPC) and glycophorin D (GPD) are homologous sialoglycoproteins in the human red blood cell membrane. Both are thought to be encoded by the GPC gene (GYPC). We report that the rare blood group antigen, Ana, is expressed on GPD but not on GPC. cDNA was synthesized from total RNA obtained from two unrelated, heterozygous Ana+ blood donors and analyzed by the polymerase chain reaction using primers that spanned sequences encoded by the GYPC gene. The expected 412-bp fragment was generated, and sequencing of the amplified product showed a G-->T substitution at nucleotide 67 of the coding sequence, resulting in the substitution of alanine by serine at amino acid residue 23 of GPC and, presumably, residue 2 of GPD. To explain the expression of Ana on GPD but not on GPC, we postulate that the conformation of the amino acid residues at the N-terminal region of GPD determines the antigenic expression as this conformation would be different from that of the same sequence of amino acids occurring within GPC. Other possible reasons for antigen expression on a shorter protein product but not on the full-length protein product of the same gene are discussed. We extrapolate this reasoning to account for the expression of the common GE2 blood group antigen on GPD but not on GPC.

Point mutation in the glycophorin C gene results in the expression of the blood group antigen Dha

The blood group Duch (Dha) antigen is located on glycophorin C (GPC). Total RNA prepared from the reticulocyte fraction of two Dh(a+) individuals were used in the synthesis of first-strand cDNA. The first-strand cDNA served as templates for the amplification of GPC-related DNA by polymerase chain reaction (PCR). The expected PCR product consisted of 412 base pairs. On sequencing the PCR-amplified DNA, a base change (cytosine----thymidine) at nucleotide 40 of the GPC cDNA was detected. Thus, the variant GPC (GPC.Dha) on Dh(a+) red cells has a substitution of leucine by phenylalanine at amino acid residue 14.

Localization of the C termini of the Rh (rhesus) polypeptides to the cytoplasmic face of the human erythrocyte membrane

We have raised a rabbit antiserum to a synthetic peptide corresponding to the C terminus (residues 400-416) of the Rh30A polypeptide. The rabbit antiserum reacted with the Rh30B (D30) polypeptide in addition to the Rh30A (C/c and/or E/e) polypeptide(s), indicating that these proteins share homology at their C termini. The antiserum did not react with erythrocyte membranes from an individual with Rh(null) syndrome. The rabbit antiserum immunoprecipitated Rh polypeptides from erythrocyte membranes and alkali-stripped membranes, but not from intact erythrocytes. Treatment of intact red cells with carboxypeptidase Y did not affect the reactivity of the antiserum, whereas treatment of alkali-stripped and unsealed erythrocyte ghost membranes resulted in the loss of antibody binding. Carboxypeptidase A treatment of intact erythrocytes and alkali-stripped membranes had no effect on antibody binding, indicating that the C-terminal domains of the Rh polypeptides contain lysine, arginine, proline, or histidine residues. These results show that the C termini of the Rh polypeptides are located toward the cytoplasmic face of the erythrocyte membrane. Treatment of intact radioiodinated erythrocytes with bromelain followed by immunoprecipitation with monoclonal anti-D gave a band of M(r) 24,000-25,000, indicating that the Rh30B (D30) polypeptide is cleaved at an extracellular domain close to the N or C terminus, with loss of the major radioiodinated domain. Immunoblotting of bromelain treated D-positive erythrocyte membranes with the rabbit antiserum to the C-terminal peptide revealed a new band of M(r) 6000-6500, indicating that the extracellular bromelain cleavage site is located near the C terminus of the molecule. The band of M(r) 6000-6500 was not obtained in erythrocyte membranes derived from bromelain treated D-negative erythrocytes. Erythrocytes of the rare -D- phenotype appear to either totally lack, or have gross alterations in, the Cc/Ee polypeptide(s), since the bromelain treatment of these cells resulted in the total loss of staining in the M(r) 35,000-37,000 region and the concomitant appearance of the new band of M(r) 6000-6500.

New monoclonal antibodies in CD59: use for the analysis of peripheral blood cells from paroxysmal nocturnal haemoglobinuria (PNH) patients and for the quantitation of CD59 on normal and decay accelerating factor (DAF)-deficient erythrocytes

CD59 is a widely expressed cell surface glycosylphosphatidylinositol (GPI)-linked glycoprotein which acts as an inhibitor of the assembly of the membrane attack complex of autologous complement. Four new monoclonal antibodies to CD59 (2/24, 1B2, BRIC 229, BRIC 257) are described. Competitive binding experiments using these antibodies, two known CD59 antibodies (MEM-43, YTH 53.1) and a previously described antibody LICR-LON-Fib75.1 demonstrated that all seven antibodies see related epitopes on human erythrocyte CD59. In common with other GPI-linked proteins, CD59 (as defined by antibody 2/24) was sensitive to treatment with phosphatidylinositol-specific phospholipase C (PI-PLC) on lymphocytes and monocytes but not on erythrocytes. Flow cytometric analysis using antibody 2/24 identified two populations (CD59 positive and CD59 deficient) of lymphocytes, monocytes and erythrocytes in peripheral blood from a patient with paroxysmal nocturnal haemoglobinuria (PNH). The abundance of CD59 on normal erythrocytes was determined as 21,000 copies/cell when radioiodinated BRIC 229 was used. Other CD59 antibodies gave values of 10,000 (IF5) and 15,000 (2/24) against the same target cells. Radioiodinated Fab fragments of BRIC 229 gave a value of 39,000 copies/cell. Erythrocytes from two individuals with a rare inherited deficiency of decay accelerating factor (DAF), known as the Inab phenotype, expressed normal levels of CD59.

Biochemical studies on red blood cells from a patient with the Inab phenotype (decay-accelerating factor deficiency)

A 38-year-old Russian woman (KZ) has been identified as the fourth proposita with the Inab blood group phenotype. Like the first two propositi, she has a chronic intestinal disorder and, as shown for the third proposita, her Inab phenotype is demonstrably inherited. KZ's serum contained anti-IFC, which reacted with a red blood cell (RBC) membrane component with an Mr of 70,000, which is decay accelerating factor (DAF). Her RBCs lacked all Cromer-related blood group antigens and DAF. Her RBCs were no more susceptible than normal control RBCs to lysis in acid lysis or in rabbit or human antibody-initiated complement lysis tests. Northern blots of total RNA isolated from KZ's Epstein-Barr virus-transformed lymphoblasts showed a marked reduction of DAF mRNA when compared with normal. Polymerase chain reaction (PCR) amplification of cDNA confirmed this reduced level of DAF mRNA. Sequencing of the PCR product showed a 44-nucleotide deletion in the mRNA close to the short consensus repeats IIIa/IIIb intron/exon boundary. This deletion results in a change in the reading frame that places a termination codon six amino acids after the deletion. The putative translation product would lack a glycosyl phosphatidyl-inositol linkage site and, therefore, would not be membrane-bound in the RBC.

New monoclonal antibodies in CD44 and CD58: their use to quantify CD44 and CD58 on normal human erythrocytes and to compare the distribution of CD44 and CD58 in human tissues

The cell-surface glycoproteins CD44 and CD58 are involved in cell adhesion reactions. In this paper 12 monoclonal antibodies in CD44 and two in CD58 are described. Competitive binding assays using CD44 antibodies identified three distinct epitope groups. Antibodies in Group 1 and, with one exception (BRIC 214), antibodies in group 2, but not antibodies in Group 3, recognized epitopes that are sensitive to reduction and to trypsin or chymotrypsin treatment of intact erythrocytes, and so these epitopes probably reside on the N-terminal disulphide-bonded domain of CD44. Antibodies in CD44 did not inhibit the binding of CD58 antibodies to erythrocytes or vice versa. Quantitative binding studies using radioiodinated IgG measured 1888-5592 copies of CD44 and 1772-3290 copies of CD58 on normal erythrocytes. Similar measurements with radioiodinated Fab fragments gave values of 6508-10,450 (CD44) and 3457-7622 (CD58). Immunocytochemical studies indicated that CD44 is much more widely expressed in non-haemopoietic tissues than CD58. Comparison with previously described CD44 antibodies suggests that antibodies in our Group 1 encompass Hermes 2 and that those in Group 2 encompass Hermes 1. All the CD44 antibodies gave weakened reactions with Lu(a-b-) erythrocytes of the In(Lu) type by one or more methods. BRIC 214 and antibodies in epitope Group 3 were used to demonstrate that CD44 on these variant cells gives membrane-bound trypsin and chymotrypsin cleavage fragments of similar molecular weight to those obtained with normal erythrocytes.

Murine monoclonal antibody MB-2D10 recognizes Rh-related glycoproteins in the human red cell membrane

The human red cell membrane components reacting with monoclonal antibody MB-2D10 were examined by immunoblotting. The antibody bound to a diffusely staining band extending from Mr 30,000 up to the high-molecular-weight region of the gel in normal membranes and in Rhnull U + membranes, but not in Rhnull U - membranes. Treatment of normal red cells with an endoglycosidase F-containing preparation destroyed the epitope recognized by MB-2D10. The reactivity of the antibody with purified preparations of Rh-related glycoproteins D30 polypeptide, D50 polypeptide, R6A32 polypeptide, and R6A45 polypeptide was also examined. Only the purified R6A45 and D50 components reacted with MB-2D10. These results show that MB-2D10 recognizes a carbohydrate-dependent epitope on the R6A45 and D50 group of Rh-related polypeptides. The results also suggest the possibility that the U antigen arises from interaction between glycophorin B and the Rh-related components D50 and R6A45.

Studies on the defect which causes absence of decay accelerating factor (DAF) from the peripheral blood cells of an individual with the Inab phenotype

1. We have studied the peripheral blood cells of an individual with the Inab phenotype who is deficient in decay accelerating factor (DAF). 2. In contrast with the situation in paroxysmal nocturnal haemoglobinuria, membranes from peripheral blood cells of the Inab phenotype individual lack DAF, but retain the other glycosylphosphatidylinositol-linked proteins acetylcholinesterase and LFA-3. 3. Unlike normal Epstein-Barr-virus-transformed lymphoblastoid cell lines (EBV-LCL), DAF was not expressed on EBV-LCL derived from peripheral blood lymphocytes of the Inab individual. 4. No differences in the DAF gene of normal and Inab phenotype individuals could be detected by Southern blotting studies. 5. EBV-LCL derived from the Inab individual had a gross reduction in the level of DAF mRNA compared with normal EBV-LCL. 6. Our results suggest that the DAF gene in the Inab phenotype contains a mutation which affects the transcription or processing of DAF mRNA.

Effect of endoglycosidase F-peptidyl N-glycosidase F preparations on the surface components of the human erythrocyte

Endo-N-acetyl-beta-D-glucosaminidase F-Peptidyl N-glycosidase F preparations (abbreviated Endo F) and endo-beta-D-galactosidase were used to study the major human erythrocyte membrane glycoproteins and the components carrying the blood group A, B, Rhesus (D), and Duffy (Fya) antigens. The results are consistent with the known presence of an N-glycosyl-linked oligosaccharide on sialoglycoprotein alpha and the absence of such an oligosaccharide from sialoglycoprotein delta. Under the conditions used, only a portion of the N-glycosyl-linked oligosaccharides on band 3 molecules were cleaved by Endo F alone or by Endo F in combination with endo-beta-D-galactosidase. Immunoblotting experiments showed that treatment of red cells with Endo F alone had little effect on the components carrying blood group A and B antigen activity. However, Endo F used in combination with endo-beta-D-galactosidase caused a substantial reduction in the binding of monoclonal anti-A and anti-B antibodies. The results clearly show that sialoglycoproteins alpha and delta carry little or no blood group A or B activity. Endo F alone, or in combination with endo-beta-D-galactosidase, had no effect on the electrophoretic mobility of the Rh(D) polypeptide, supporting previous suggestions that this membrane polypeptide is unusual in not being glycosylated. Endo F had a dramatic effect on the electrophoretic mobility of the component(s) carrying blood group Fya activity. The diffuse Fya component of Mr 38,500-90,000 was sharpened to a band of Mr 26,000. Either endo-beta-D-galactosidase or neuraminidase treatment reduced the Mr of the Fya component(s) but did not significantly sharpen the bands, suggesting that the Fya component contains between 40-50% by mass of N-glycosyl-linked oligosaccharides.

The Ina and Inb blood group antigens are located on a glycoprotein of 80,000 MW (the CDw44 glycoprotein) whose expression is influenced by the In(Lu) gene

The Ina and Inb blood group antigens were found to be located on an erythrocyte membrane glycoprotein of 80,000 MW by immunoblotting with human anti-Ina and anti-Inb antibodies under non-reducing conditions. This glycoprotein is shown here to be identical to that defined by monoclonal antibodies to CDw44, and a new murine monoclonal antibody (BRIC 35) is added to this cluster. Experiments with endo-beta-galactosidase and Endo F preparations suggest that the glycoprotein contains one or more N-glycans but that these oligosaccharides do not contain extensive poly-N-acetyllactosaminyl sequences. Experiments using membranes prepared from sialidase-treated normal erythrocytes, from Tn erythrocytes and from Cad erythrocytes suggest that the glycoprotein does not contain a substantial content of O-glycans. The Inb antigen and the epitope defined by a murine monoclonal antibody (BRIC 35) show reduced expression on Lu(a-b-) erythrocytes which result from the effect of the dominant inhibitor gene In(Lu). Evidence is presented here that the Inb antigen is expressed on normal granulocytes and lymphocytes and on the haemopoietic cell lines HEL, K562 and HL-60, a lymphoblastoid cell line and lymphocytes from two patients with B-CLL.

Monoclonal antibodies that recognize different membrane proteins that are deficient in Rhnull human erythrocytes. One group of antibodies reacts with a variety of cells and tissues whereas the other group is erythroid-specific

1. Rhnull human erythrocytes lack all of the antigens of the Rh and LW blood group systems and have abnormal shape and an increased osmotic fragility. In this paper two murine monoclonal antibodies raised against intact human erythrocytes were used to investigate further the abnormalities in these cells. BRIC 125 reacts weakly with Rhnull erythrocytes and BRIC 69 does not react at all. The results showed that BRIC 125 reacts with a component of Mr 47,000-52,000 which has a substantial content of N-glycans. In contrast, BRIC 69 reacted with a band of Mr 31,000 together with a very diffuse band of Mr 35,000-52,000. Treatment of BRIC 69 immunoprecipitates with endoglycosidase F/peptidyl-N-glycosidase F resulted in the loss of both BRIC 69 reactive components and the appearance of a new band of Mr similar to that of the Rh(D) polypeptide. 2. BRIC 125 had a broad reactivity with cells in peripheral blood, whereas the reactivity of BRIC 69 was confined to erythrocytes. BRIC 125, but not BRIC 69, reacted with human kidney tissue and bound to endothelium in peritubular capillaries, arteries and veins as well as the epithelial tissue of distal tubules. BRIC 125 stained haemopoietic cells, foetal hepatocytes and megakaryocytes in foetal liver and sinusoidal cells, hepatocytes and portal tracts in adult liver. In contrast, BRIC 69 reactivity was confined to haemopoietic cells in foetal liver. The BRIC 125 epitope has a wide tissue distribution, suggesting the occurrence of a related group of polypeptides which have a general functional role on cell surfaces. 3. Rhnull erythrocytes are deficient in at least four different membrane polypeptides.

A human cell-surface glycoprotein that carries Cromer-related blood group antigens on erythrocytes and is also expressed on leucocytes and platelets

A new human erythrocyte glycoprotein has been identified by immunoblotting with murine monoclonal antibodies under non-reducing conditions. The glycoprotein has a MW of 70,000 and carries Cromer-related blood group antigens. The monoclonal antibodies also react with normal peripheral blood leucocytes and platelets and several haemopoietic cell lines. The glycoprotein has a reduced MW after sialidase treatment. The MW is markedly reduced in Tn erythrocyte membranes and slightly increased in Cad erythrocyte membranes. These results suggest that the glycoprotein has a substantial content of O-glycans. The glycoprotein appears to be absent from, or grossly altered in, the erythrocytes of two individuals with the rare Inab phenotype.

Evidence that the Lub blood group antigen is located on red cell membrane glycoproteins of 85 and 78 kd

A murine monoclonal antibody of specificity anti-Lub was produced. Immunoblotting of the electrophoretically separated components of membranes from Lu(b+) red cells with the monoclonal antibody identified two glycoproteins of relative molecular mass 85 and 78 kd, respectively. The expression of Lub antigenic activity on these glycoprotein components was shown to be dependent on the presence of one or more N-glycosidically linked oligosaccharides and on the presence of disulphide bonding.

Identification and partial characterization of the human erythrocyte membrane component(s) that express the antigens of the LW blood-group system

Rhnull human erythrocytes lack the antigens of the Rhesus blood-group system, have an abnormal shape, have an increased osmotic fragility, and are associated with mild chronic haemolytic anaemia. Rhnull erythrocytes also lack all antigens of the LW blood-group system, but the functional significance of this deficiency is unknown. We have identified, by immunoblotting with two mouse monoclonal antibodies (BS46 and BS56), the LW-active component(s) in normal human erythrocytes as a broad band of Mr 37 000-47 000 on SDS/polyacrylamide-gel electrophoresis. Treatment of intact human erythrocytes with endoglycosidase F preparation destroyed the epitopes recognized by antibodies BS46 and BS56, suggesting that one or more N-glycosidically linked oligosaccharides are required for the formation of the LW antigens. Estimation of the number of LW antigen sites per erythrocyte by using radioiodinated purified antibody BS46 gave average values of 4400 molecules/cell for Rh(D)-positive adult erythrocytes and 2835 molecules/cell for Rh(D)-negative adult erythrocytes. Like the Rh(D) polypeptide, the LW polypeptide(s) is (are) associated with the cytoskeleton of normal erythrocytes. These results suggest the possibility that the absence of the LW polypeptide may also contribute to the functional and/or morphological abnormalities of Rhnull erythrocytes.