Enzyme Immunoassay for the Detection of RUBELLA IgG Antibody
Introduction
Rubella virus is classified as a togavirus and is the only member of the Rubivirus genus. The virus consists of a single-strand RNA, an inner icosahedral nucleocapsid, and a lipoprotein envelope.
Rubella (German measles, 3-day measles) is an acute febrile illness that manifests with various signs and symptoms, including skin rash, posterior auricular, and suboccipital lymphadenopathy. Among viral infections with skin rash manifestations, Rubella virus causes the mildest disease. However, during pregnancy, the virus can cause Congenital Rubella Syndrome (CRS), which leads to serious fetal complications depending on the gestational age at the time of infection. Maternal infection during early pregnancy (first trimester) results in congenital abnormalities in approximately 85% of neonates, while infections during the second trimester reduce this percentage to 15%. Fetal abnormalities caused by Rubella virus include mental retardation, heart disease, cataracts, deafness, meningoencephalopathy, and progressive panencephalitis. Infections during the third trimester often result in no obvious fetal symptoms.
Detection of specific anti-Rubella IgG corresponds to immunity against the virus. Diagnosing Rubella infection during pregnancy is crucial. To reliably diagnose Rubella infection, two separate serum samples taken 10 days apart should be used to demonstrate a rising specific anti-Rubella IgG titer. An alternative serological technique for diagnosing Rubella infection is the demonstration of specific anti-Rubella IgM antibodies in an individual sample. Hemagglutination inhibition (HI) and ELISA are considered standard techniques for diagnosing Rubella infection. Since the HI method requires pretreatment to remove nonspecific inhibitors, ELISA is preferred.
Clinical Significance
Rubella IgG testing is critical for determining immune status, particularly in women of childbearing age, to prevent congenital rubella syndrome. A positive Rubella IgG test indicates past infection or successful vaccination, providing lifelong immunity. Conversely, a negative result suggests susceptibility to Rubella infection, emphasizing the need for vaccination. The quantitative measurement of Rubella IgG antibodies assists in monitoring immune responses and vaccine efficacy.
Test Principle
The test principle is based on the indirect ELISA technique, in which diluted patient serum samples react with coated Rubella antigens. After incubation, an anti-human IgG conjugated with HRP is added to the wells. If anti-Rubella IgG is present in the samples, it reacts with the HRP-conjugated anti-human IgG. After incubation and appropriate washing, a chromogen substrate solution is added and incubated for 15 minutes, resulting in the development of a blue color. The color development is stopped with the addition of stop solution, changing the color to yellow, which is measured spectrophotometrically at 450 nm. The concentration of Rubella IgG is directly proportional to the color intensity of the test sample.
References
- Centers for Disease Control and Prevention. Rubella and congenital Rubella syndrome – United States, 1994-1997. MMWR 1997;46:350-4.
- de Souza VA, Sumita LM, Otsubo ME, Takei K, Pannuti CS. Enzyme-linked immunosorbent assay for Rubella antibodies: A simple method of antigen production. Rev Inst Med Trop Sao Paulo 1995;37(4):357-9.
- Engvall E, Perlmann P. Enzyme-linked immunosorbent assay (ELISA): Quantitative assay for immunoglobulin. J Immunochemistry 1977;8:871-874.
- Brooks GF, Butel SJ. Jawetz, Melnick, & Adelberg’s Medical Microbiology. 22nd edition. McGraw-Hill; 2001.
- Murray PR, Rosenthal KS, Kobayashi GS. Medical Microbiology. 4th edition. Mosby; 2002.