Analysis of measles virus binding sites of the CD46 gene in patients with subacute sclerosing panencephalitis

Mutations in genes encoding complement inhibitors CD46 and CFH affect the age at nephritis onset in patients with systemic lupus erythematosus

Introduction

Inherited deficiencies of several complement components strongly predispose to systemic lupus erythematosus (SLE) while deficiencies of complement inhibitors are found in kidney diseases such as atypical hemolytic uremic syndrome (aHUS).

Methods

The exons of complement inhibitor genes CD46 and CFH (factor H) were fully sequenced using the Sanger method in SLE patients with nephritis originating from two cohorts from southern and mid Sweden (n = 196). All identified mutations and polymorphisms were then analyzed in SLE patients without nephritis (n = 326) and in healthy controls (n = 523).

Results

We found nonsynonymous, heterozygous mutations in CFH in 6.1% patients with nephritis, in comparison with 4.0% and 5.4% in patients without nephritis and controls, respectively. No associations of SLE or nephritis with common variants in CFH (V62I/Y402H/E936D) were found. Furthermore, we found two nonsynonymous heterozygous mutations in CD46 in SLE patients but not in controls. The A353V polymorphism, known to affect function of CD46, was found in 6.6% of nephritis patients versus 4.9% and 6.1% of the non-nephritis SLE patients and controls. The presence of mutations in CD46 and CFH did not predispose to SLE or nephritis but was associated with earlier onset of nephritis. Furthermore, we found weak indications that there is one protective and one risk haplotype predisposing to nephritis composed of several polymorphisms in noncoding regions of CD46, which were previously implicated in aHUS.

Conclusions

SLE nephritis is not associated with frequent mutations in CFH and CD46 as found in aHUS but these may be modifying factors causing earlier onset of nephritis.

Measles virus and CD46

Measles virus (MV) was isolated in 1954 (Enders and Peeble 1954). It is among the most contagious of viruses and a leading cause of mortality in children in developing countries (Murray and Lopez 1997; Griffin 2001; Bryce et al. 2005). Despite intense research over decades on the biology and pathogenesis of the virus and the successful development in 1963 of an effective MV vaccine (Cutts and Markowitz 1994), cell entry receptor(s) for MV remained unidentified until 1993. Two independent studies showed that transfection of nonsusceptible rodent cells with human CD46 renders these cells permissive to infection with the Edmonston and Halle vaccine strains of measles virus (Dorig et al. 1993; Naniche et al. 1993). A key finding in these investigations was that MV binding and infection was inhibited by monoclonal and polyclonal antibodies to CD46. These reports established CD46 as a MV cell entry receptor. This chapter summarizes the role of CD46 in measles virus infection.

Variations in measles vaccine–specific humoral immunity by polymorphisms in SLAM and CD46 measles virus receptors

BACKGROUND

Measles infection requires 2 cellular receptors, signaling lymphocyte activation molecule (SLAM) and CD46. Known and novel single nucleotide polymorphisms (SNPs) in SLAM and CD46 genes might influence the immune response to measles vaccine.

OBJECTIVE

We sought to identify SNP associations in SLAM and CD46 genes with variations in measles antibody response.

METHODS

We genotyped known SNPs in SLAM and CD46 genes in 339 subjects vaccinated with 2 doses of measles-mumps-rubella vaccine. We also sequenced the measles virus-binding domains of SLAM and CD46 to identify novel SNPs.

RESULTS

Increased representation of minor alleles for rs3796504 and rs164288 in the SLAM gene was associated with an allele dose-related decrease (4-fold) in measles-specific antibodies. Heterozygous genotype TC for rs12076998 located in the untranslated region 33 bp upstream of the measles virus-binding domain of the SLAM gene was associated with higher median antibody levels (1991 vs 1467 IU/L, P = .01) compared with wild-type TT. Within the CD46 gene, the minor allele C for intronic SNP (rs11118580) was associated with an allele dose-related decrease in measles antibodies (1072 vs 1795 IU/L, P < .01). Decreases in minor allele counts for rs3796504, rs164288, and rs1118580 demonstrated a significant (P < .001) additive effect on measles-specific antibodies.

CONCLUSION

Our data suggest that specific SNPs present in both the SLAM and CD46 genes are associated with measurable and significant variations in antibody response after measles vaccination.

CLINICAL IMPLICATIONS

Understanding the immunogenetics of measles vaccine receptors is important to better understand variations in immune responses to vaccines and to design better vaccines.

Angiotensin-converting enzyme and angiotensin II type 1 receptor gene polymorphisms in children with subacute sclerosing panencephalitis

Subacute sclerosing panencephalitis (SSPE) is a progressive, debilitating, and fatal brain disorder caused by mutant measles virus infection. Although both viral and host factors seem to be involved in SSPE, the exact pathogenesis remains to be determined. Autoimmune demyelination is characteristic of SSPE. The blood angiotensin-converting enzyme (ACE) activity and angiotensin II (Ang II) levels are associated with the ACE gene polymorphism. Proinflammatory effects of Ang II may contribute to the development of SSPE. The aim of this study was to investigate whether the ACE and Ang II type 1 receptor (AT1R) (A1166C) gene polymorphisms were associated with SSPE. The polymorphisms were investigated by polymerase chain reaction (PCR) in 43 patients with SSPE and 100 healthy controls. The genotype distribution of the SSPE children and healthy controls were as follows: DD 58.1% versus 34.0, ID 37.2% versus 48.0%, and II 4.7% versus 18.0, respectively (P = 0.012). Allele frequencies of patients and controls were D 76.7% versus 58.0%, and I 23.3% versus 42.0%, respectively (P = 0.004). The frequency of DD genotype and D allele were significantly higher in SSPE children compared with controls (P < 0.05). AT1R gene polymorphism distribution was found to be similar in SSPE children and control subjects: AA 55.8% versus 60.7%, AC 37.2% versus 32.1%, and CC 7.0% versus 7.2%, respectively (P > 0.05). In conclusion, the results of this study suggest that the DD genotype of ACE I/D polymorphism may be related to SSPE. Due to small size of this study, further studies with more patients are needed to confirm these results.

Gene expression profiles in peripheral blood mononuclear cells from patients with subacute sclerosing panencephalitis using oligonucleotide microarrays

To investigate the molecular basis for measles virus persistence in patients with subacute sclerosing panencephalitis (SSPE), the authors used a high-density oligonucleotide microarray, and found that the expression of granulysin in peripheral blood mononuclear cells was significantly lower in the patients than in the controls. By a quantitative reverse transcriptase-polymerase chain reaction, the mRNA levels of granulysin were decreased in 30 SSPE patients, and were increased in 7 measles patients, as compared to the 23 controls. These results imply that granulysin might play a role in the host defense against measles virus and possibly be involved in the pathogenesis or pathophysiology of SSPE.

Interleukin-4 induced by measles virus and measles-derived peptides as measured by IL-4 receptor-blocking ELISA

Interleukin-4 (IL-4) is a signature cytokine for T-helper 2 (Th2) type immune responses in humans. However, data on antigen-specific secretion of IL-4 is limited due to difficulties detecting IL-4. We evaluated an IL-4 receptor-blocking assay for the detection of secreted IL-4 in peripheral blood mononuclear cells (PBMC) stimulated in vitro with measles virus (MV) and MV-derived nucleoprotein (N) and phosphoprotein (P) peptides. We recruited 20 healthy subjects, previously immunized with two doses of measles-mumps-rubella-II (MMR-II) vaccine. We evaluated the cellular and humoral immune status of these study subjects by an in vitro lymphoproliferation assay and an enzyme-linked immunosorbent assay (ELISA), respectively. We analyzed the MV-induced and N and P peptide-induced IL-4 levels in PBMC culture supernatants. Using the IL-4 receptor blocking assay, 50% of the subjects were positive for secreted IL-4 in response to MV stimulation, and 5% and 23.1% of study subjects were positive for secreted IL-4 in response to MV-derived N and P peptides, respectively. In contrast, we did not find any positive secreted IL-4 response to MV using conventional ELISA without IL-4 receptor-blocking antibody in our optimization study. Further, we found very low frequencies of IL-4 secreting cells using an alternate ELISpot technique, accounting for only a 5% positive response to MV and no response to P peptide. We propose that the IL-4 receptor-blocking assay is an easy-to-adapt technique for screening antigen-specific immune responses in large-scale population-based studies.