Mapping of the Epstein-Barr virus and C3dg binding sites to a common domain on complement receptor type 2.

Complement receptor type 2 (CR2;CD21), a member of the superfamily of proteins containing short consensus repeats (SCRs), is the B cell receptor for both the gp350/220 envelope protein of Epstein-Barr virus (EBV), and for the C3dg protein of complement. By analysis of CR2 deletion mutants and chimeras formed with CR1 (CD35) we determined that of the 15 SCRs in CR2, the NH2-terminal two SCRs are necessary and sufficient to bind both gp350/220 and C3dg with affinities equivalent to those of the wild-type receptor. The epitope for OKB-7, a mAb that blocks binding of both EBV and C3dg and shares with these ligands B cell-activating capabilities, also requires both SCR-1 and SCR-2, whereas mAbs lacking these functions bind to other SCRs. Thus, EBV, a polyclonal activator of B cells, has selected a site that is proximate or identical to the natural ligand binding site in CR2, perhaps reflecting the relative immutability of that site as well as its signal transducing function

Functional characterization of the complement receptor type 1 and its circulating ligands in patients with schizophrenia

<p>Abstract</p> <p>Background</p> <p>Whereas the complement system alterations contribute to schizophrenia, complement receptors and regulators are little studied. We investigated complement receptor type 1 (CR1) expression on blood cells, the levels of circulating immune complexes (CIC) containing ligands of CR1, C1q complement protein and fragments of C3 complement protein (C1q-CIC, C3d-CIC), and CR1 C5507G functional polymorphism in schizophrenia patients and controls.</p> <p>Results</p> <p>We found an increased C1q-CIC level and CR1 expression on blood cells, elevated number of CR1 positive erythrocytes and reduced number of CR1 positive lymphocytes and monocytes in patients compared to controls. No difference in the levels of C3d-CIC between groups was observed. Higher CR1 expression on erythrocytes in CC genotype versus CG+GG for both groups was detected, whereas no difference was observed for other cell populations. Our results indicated that schizophrenia is associated with the increased CR1 expression and C1q-CIC level.</p> <p>Conclusions</p> <p>Our study for the first time indicated that schizophrenia is associated with the increased CR1 expression and C1q-CIC level. Further studies in other ethnic groups are needed to replicate these findings.</p

Analysis of the putative role of CR1 in Alzheimer’s disease: Genetic association, expression and function

Chronic activation of the complement system and induced inflammation are associated with neuropathology in Alzheimer's disease (AD). Recent large genome wide association studies (GWAS) have identified single nucleotide polymorphisms (SNPs) in the C3b/C4b receptor (CR1 or CD35) that are associated with late onset AD. Here, anti-CR1 antibodies (Abs) directed against different epitopes of the receptor, were used to localize CR1 in brain, and relative binding affinities of the CR1 ligands, C1q and C3b, were assessed by ELISA. Most Abs tested stained red blood cells in blood vessels but showed no staining in brain parenchyma. However, two monoclonal anti-CR1 Abs labeled astrocytes in all of the cases tested, and this reactivity was preabsorbed by purified recombinant human CR1. Human brain-derived astrocyte cultures were also reactive with both mAbs. The amount of astrocyte staining varied among the samples, but no consistent difference was conferred by diagnosis or the GWAS-identified SNPs rs4844609 or rs6656401. Plasma levels of soluble CR1 did not correlate with diagnosis but a slight increase was observed with rs4844609 and rs6656401 SNP. There was also a modest but statistically significant increase in relative binding activity of C1q to CR1 with the rs4844609 SNP compared to CR1 without the SNP, and of C3b to CR1 in the CR1 genotypes containing the rs6656401 SNP (also associated with the larger isoform of CR1) regardless of clinical diagnosis. These results suggest that it is unlikely that astrocyte CR1 expression levels or C1q or C3b binding activity are the cause of the GWAS identified association of CR1 variants with AD. Further careful functional studies are needed to determine if the variant-dictated number of CR1 expressed on red blood cells contributes to the role of this receptor in the progression of AD, or if another mechanism is involved

No Evidence that Knops Blood Group Polymorphisms Affect Complement Receptor 1 Clustering on Erythrocytes

Clustering of Complement Receptor 1 (CR1) in the erythrocyte membrane is important for immune-complex transfer and clearance. CR1 contains the Knops blood group antigens, including the antithetical pairs Swain-Langley 1 and 2 (Sl1 and Sl2) and McCoy a and b (McCa and McCb), whose functional effects are unknown. We tested the hypothesis that the Sl and McC polymorphisms might influence CR1 clustering on erythrocyte membranes. Blood samples from 125 healthy Kenyan children were analysed by immunofluorescence and confocal microscopy to determine CR1 cluster number and volume. In agreement with previous reports, CR1 cluster number and volume were positively associated with CR1 copy number (mean number of CR1 molecules per erythrocyte). Individuals with the McCb/McCb genotype had more clusters per cell than McCa/McCa individuals. However, this association was lost when the strong effect of CR1 copy number was included in the model. No association was observed between Sl genotype, sickle cell genotype, α+thalassaemia genotype, gender or age and CR1 cluster number or volume. Therefore, after correction for CR1 copy number, the Sl and McCoy polymorphisms did not influence erythrocyte CR1 clustering, and the effects of the Knops polymorphisms on CR1 function remains unknown

Characterization of two novel LPS-binding sites in leukocyte integrin βA domain

Lipopolysaccharide (LPS), a bacterial endotoxin, triggers deleterious systemic inflammatory responses when released into blood circulation, causing organ dysfunction and death. In response to LPS stimulation, CD14 and toll-like receptor (TLR)-4 elicit inflammatory signaling cascades. Although leukocyte integrins (CD11b/CD18 and CD11c/CD18) were reported to bind LPS and induce NF-κB translocation, the evidence on such epitope location remains elusive. The present study aims to delineate the LPS-binding sites on the integrin CD18 antigen and to design peptide(s) as potential prophylactic and/or therapeutic agents to modulate LPS effects in activated Jurkat cells. Epitope mapping analysis using a series of CD18 truncated variants revealed two putative LPS-binding sites within the βA region (216-248 and 266-318 a.a.), which were further confirmed by point mutation studies. Inhibition assay demonstrated that the CD18-βA266-318 peptide could block LPS binding in a dosedependent manner. Our data also indicated that treatment with the CD18-peptide modulated TNF-α mRNA transcription via the NF-κB signaling pathway in LPS-activated Jurkat cells. In conclusion, we have identified two novel LPS-binding sites located at the CD18 βA domain of leukocyte integrin, and the integrin peptide βA266-318 is shown to inhibit LPS binding and subsequent inflammatory events, having therapeutic implications to cure Gram-negative endotoxemia. © FASEB.link_to_subscribed_fulltex