Increased frequency of the long (S) allotype of CR1 (the C3b/C4b receptor, CD35) in patients with systemic lupus erythematosus

CR1 exon variants are associated with lowered CR1 expression and increased susceptibility to SLE in a Plasmodium falciparum endemic population

BACKGROUND

Complement receptor 1 (CR1) plays an important role in immune complex clearance by opsonisation and possibly protects subjects from development of autoantibodies. Lower CR1 expression has been associated with susceptibility to systemic lupus erythematosus (SLE). In contrast, subjects displaying lower CR1 expression are protected against severe manifestations of falciparum malaria. This study is the first of its kind to investigate the association of CR1 variants with development of SLE in a P. falciparum endemic population from Odisha, India.

METHODS

CR1 polymorphisms (intron 27 (A>T), exon 22 (A>G) and exon 33 (G>C)) were typed by PCR and restriction length polymorphism in 297 cases of female patients with SLE and 300 age-matched and sex-matched healthy controls from malaria endemic areas in Odisha, India. CR1 expression on monocytes was quantified by flow cytometry.

RESULTS

The homozygous mutants of CR1 exon 22 (GG) and exon 33 (GG) and their minor alleles were associated with susceptibility to SLE. Furthermore, patients with SLE who harboured the GG genotype of the exon 33 polymorphism had a 3.12-fold higher chance of developing lupus nephritis. CR1 exon (22 and 33) variants were associated with lowered CR1 expression on monocytes in patients with SLE and in healthy controls. Patients with lupus nephritis showed significantly diminished CR1 expression than those without renal involvement (p=0.01).

CONCLUSIONS

The results of the present study demonstrate that common CR1 exon variants are associated with diminished CR1 expression on monocytes and increased susceptibility to development of SLE and lupus nephritis in a malaria endemic area.

The presence of CD55- and/or CD59-deficient erythrocytic populations in patients with rheumatic diseases reflects an immune-mediated bone-marrow derived phenomenon

Background

Complement has the potential to provoke severe impairment to host tissues, as shown in autoimmune diseases where complement activation has been associated with diminished CD55 and/or CD59 expression on peripheral blood cell membranes. The aim of this study was to evaluate the presence of CD55- and/or CD59-deficient erythrocytic populations in patients with different rheumatic diseases and to investigate possible correlations with clinical or laboratory parameters.

Material/Methods

CD55 and CD59 expression was evaluated in erythrocytes of 113 patients with rheumatic diseases, 121 normal individuals, and 10 patients with paroxysmal nocturnal hemoglobinuria (PNH) using the Sephacryl gel microtyping system. Ham and sucrose tests were also performed.

Results

Interestingly, the majority of patients (104/113, 92%) demonstrated CD55- and/or CD59-deficient erythrocytes: 47 (41.6%) with concomitant deficiency of CD55 and CD59, 50 (44.2%) with isolated deficiency of CD55, and 6 (6.2%) with isolated deficiency of CD59. In normal individuals, only 2 (1%) had concomitant CD55/CD59 negativity and 3 (2%) had isolated CD55 or CD59 deficiency. All PNH patients exhibited simultaneous CD55/CD59 deficiency. Positive Ham and sucrose tests were found only in PNH patients. There was no association between the CD55- and/or CD59-deficient erythrocytes and hemocytopenias or undergoing treatment. However, CD55 expression significantly influenced hemoglobin values (F=6.092, p=0.015).

Conclusions

This study provides evidence supporting the presence of erythrocytes with CD55 and/or CD59 deficiency in patients with rheumatic diseases. Moreover, CD55 deficiency on red cells influences hemoglobin concentration. Further studies using molecular techniques will clarify the exact pathophysiological mechanisms of this deficiency.

The role of complement regulatory proteins in peripheral blood cells of patients with systemic lupus erythematosus: review

CD55, CD59, CD35 and CD46 are cell membrane proteins that have regulatory properties on the activation of the complement cascade. Deficiency in the expression of these proteins may be associated with lower protection of healthy cells against complement mediated lysis and also with the accumulation of immune complexes in tissues. Few studies assess the expression of these proteins in patients with SLE and the mechanisms that regulate reduction in cellular expression, whereas its impact on manifestations of systemic lupus erythematosus is still unknown.

Polymorphisms of complement receptor 1 and interleukin-10 genes and systemic lupus erythematosus: a meta-analysis

A number of studies have tested the association of the complement receptor 1 (CR1) and Interleukin-10 (IL10) polymorphisms with systemic lupus erythematosus (SLE), but reported conflicting results. The aim of the study is to explore whether the CR1 and IL10 genes are associated with SLE susceptibility. We surveyed studies on the CR1 and IL10 polymorphisms and SLE using comprehensive Medline search and review of the references. A meta-analysis was conducted in a fixed effects model or random effects model based on between-study heterogeneity. Eighteen comparisons from 13 studies were included in the CR1 meta-analysis and a total of 16 separate comparisons were used for the IL10 meta-analysis. The CR1 meta-analysis showed no significant association of the CR1 functional polymorphisms with SLE. In contrast, the S structural variant of the CR1 showed a significant association (OR=1.544, 95% CI, 1.217-1.959, P<0.001). Stratification by ethnicity indicated that the CR1 S variant was associated with SLE in Caucasians (OR=1.667, 95% CI, 1.193-2.357, P=0.003). The IL10 meta-analysis showed a significant association between SLE and the G11 allele of IL10.G (OR=1.279, 95% CI; 1.027-1.593, P=0.028) in whole populations, and IL10 promoter -1082G allele was associated with SLE in Asians (OR=1.358, 95% CI; 1.015-1.816, P=0.039). In conclusion, the CR1 meta-analysis revealed the association of the S structural variant of the CR1 with SLE and the IL10 meta-analysis showed the association of IL10.G11 allele and SLE in whole populations and the association between promoter -A1082G polymorphism and SLE in Asians.

The C3b/C4b receptor (CR1, CD35) on erythrocytes: methods for study of the polymorphisms

This report is devoted to methodologies used in analyzing the C3b/C4b receptor (CR1, CD35) on erythrocytes (E), its soluble form, the CRI structural or allotype polymorphism, and CR1 density polymorphism. In primates E CR1 serves as the main system for processing and clearance of complement opsonized immune complexes (IC). CR1 copy numbers decrease with aging of E in normal individuals. Erythrocyte CR1 is also decreased in pathological conditions such as systemic lupus erythematosus (SLE), HIV infection, certain hemolytic anemias, and many other conditions featuring immune complexes. Consequently, CRI on E has an important physiological role in immune complex handling and has interesting alterations in disease.

Evidence for linkage of a candidate chromosome 1 region to human systemic lupus erythematosus

Genetic susceptibility confers significant risk for systemic lupus erythematosus (SLE). The MHC region and other polymorphic loci have been associated with SLE. Because more compelling evidence for an involvement of a genetic locus includes linkage, we tested a candidate region homologous to a murine SLE susceptibility region in 52 SLE-affected sibpairs from three ethnic groups. We analyzed seven microsatellite markers from the human chromosome 1q31-q42 region corresponding to the telomeric end of mouse chromosome 1, the region where specific manifestations of murine lupus, including glomerulonephritis and IgG antichromatin, have been mapped. Comparing the mean allele sharing in affected sibpairs of each of these seven markers to their expected values of 0.50, only the five markers located at 1q41-q42 showed evidence for linkage (P = 0.0005-0.08). Serum levels of IgG antichromatin also showed evidence for linkage to two of these five markers (P = 0.04), suggesting that this phenotype is conserved between mice and humans. Compared to the expected random distribution, the trend of increased sharing of haplotypes was observed in affected sibpairs from three ethnic groups (P < 0.01). We concluded that this candidate 1q41-q42 region probably contains a susceptibility gene(s) that confers risk for SLE in multiple ethnic groups.

Mannose-binding protein genetic polymorphisms in black patients with systemic lupus erythematosus

OBJECTIVE

To determine whether dysfunctional or deficient mannose-binding protein (MBP) variants are found with increased frequency in black patients with systemic lupus erythematosus (SLE) compared with controls.

METHODS

Allele-specific polymerase chain reaction amplification of 4 different polymorphic sites was performed on samples from 92 black SLE patients and 86 geographically matched black controls.

RESULTS

Two structural polymorphisms of MBP, associated with low serum levels of MBP, were found with significantly increased frequency in the SLE patient population compared with controls. In contrast, a promoter haplotype associated with particularly high serum levels of MBP was negatively associated with SLE.

CONCLUSION

Deficiencies of MBP predispose individuals to SLE.

C3b receptor (CR1) genomic polymorphism in rheumatoid arthritis. Low receptor levels on erythrocytes are an acquired phenomenon

The number of complement receptor 1 (CR1, CD35) molecules on erythrocytes is genetically determined by two codominant alleles. The numerical expression of CR1 on erythrocytes correlates with a HindIII-RFLP or CR1 gene using CR1-1, a complementary DNA probe. We have found low CR1 on erythrocytes in patients with rheumatoid arthritis (RA) in an Indian population. Low levels in RA patients may be acquired or genetically determined. Fifty-two patients with RA, 48 nonrelated healthy subjects and 19 consanguineous relatives of patients were genotyped. CR1 numbers on erythrocytes were quantitated by the enzyme-linked immunosorbent assay using monoclonal anti-CR1 antibody. Normal subjects and patients were followed up for a period of 6 months to evaluate the stability of their CR1 expression. The gene frequency for allele H and L (7.4- and 6.9-kb HindIII restriction fragment, respectively), which correlated with high and low expression of CR1 on erythrocytes was 0.77 and 0.23 in the normal controls. Gene frequency in RA patients was 0.78 and 0.22 for H and L allele, which did not differ significantly from either controls or relatives (0.80 and 0.20 for H and L allele, respectively). However, RA patients expressed fewer CR1 on erythrocytes within each genotype than their relatives and controls. CR1 on erythrocytes were found to be stable in consecutive samples in controls. In RA patients, the number varied between low and high during the course of the disease. The variation in number was significantly correlated (p < 0.05, r = -0.85 to -0.98) with disease activity as monitored by erythrocyte sedimentation rate. Our results suggest that low levels of CR1 on erythrocytes in patients with RA are not inherited, rather they are acquired during the course of the disease.

Non-MHC-linked genes in autoimmune diseases

Single-locus mutations in mice associated with autoimmune manifestations or influencing them, including lpr, motheaten and xid have been characterized at the molecular level. Mutations have been described in the genes encoding Fc gamma RI, interleukin-2 and natural resistance associated macrophage protein, which are all candidate genes for susceptibility loci associated with autoimmune diabetes in non-obese diabetic mice. Twelve regions of DNA that are associated with disease susceptibility have now been identified in this polygenic model of autoimmunity. In human autoimmune diseases, the region of DNA surrounding the insulin gene that is associated with susceptibility to insulin dependent diabetes mellitus has been narrowed down to 4.1 kilobases.