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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. [ABSTRACT FROM AUTHOR]

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 distract epitope groups. Antibodies in Group I 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 m our Group I encompass Hermes 2 and that those in Group 2 encompass Hermes I. 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. [ABSTRACT FROM AUTHOR]

The Ina and Inb blood group antigens were found to he 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-β-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-acetyl lacto saminyl 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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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., (© Royal College of Physicians 2023. All rights reserved.)

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.

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.

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.