Enzyme Immunoassay for the Detection of Human Immunodeficiency Virus Type 1 and 2 Antibody & P24 Antigen
Introduction
Human Immunodeficiency Virus (HIV) belongs to the Retroviridae family and is classified into two main types: HIV-1 and HIV-2. HIV-1 is the most prevalent and widely distributed type, first identified in 1983 by Luc Montagnier in France, with its characteristics later described by Robert Gallo and Jay Levy in the United States (Barré-Sinoussi et al., 1983). HIV-2 was subsequently identified in West Africa in 1986 (Clavel et al., 1986). The viral genome is composed of single-stranded RNA approximately 9.7 Kb in length.
HIV is the etiologic agent of Acquired Immunodeficiency Syndrome (AIDS), which has a latent period of approximately eight years from initial infection to the development of clinical symptoms. During this period, the virus proliferates and gradually destroys CD4+ lymphocytes, leading to immunosuppression and increased susceptibility to opportunistic infections (Ghosn et al., 2018).
The detection of HIV infection is primarily based on identifying specific antibodies against HIV antigens. Additionally, p24 antigen detection is crucial for identifying the infection in its early stages before seroconversion. Levels of p24 antigen rise significantly within one to three weeks post-infection, making it a valuable biomarker for early diagnosis (Fiebig et al., 2003).
Clinical Significance
The fourth-generation HIV 1,2 Antigen-Antibody ELISA kit offers a highly sensitive and specific diagnostic approach by detecting both HIV antibodies and p24 antigen. This allows for the early identification of infected individuals before seroconversion, enhancing timely medical intervention and reducing transmission risks (Branson et al., 2014). The inclusion of both antigen and antibody detection ensures a broader diagnostic window and improved accuracy compared to previous generations of ELISA-based assays.
Test Principle
This assay is based on a combined antigen-antibody sandwich ELISA technique. The microtiter wells are coated with HIV-1 recombinant antigens (gp41, gp120) and HIV-2 recombinant antigen (gp36), as well as human anti-p24 HIV-1 antibody. Serum samples are then incubated with these coated wells, allowing specific HIV antibodies (IgG, IgM, IgA) and HIV-1 p24 antigen to bind.
Following incubation and washing steps, a biotin-labeled antigen-antibody complex and streptavidin-HRP conjugate are introduced. After another incubation and washing, a chromogen-substrate solution is added, leading to color development. The reaction is stopped using an acid solution, and the absorbance is measured spectrophotometrically at 450 nm. The intensity of the color is directly proportional to the concentration of HIV antibodies and p24 antigen in the sample.
References
- Barré-Sinoussi, F., Chermann, J. C., Rey, F., Nugeyre, M. T., Chamaret, S., Gruest, J., … & Montagnier, L. (1983). Isolation of a T-lymphotropic retrovirus from a patient at risk for acquired immune deficiency syndrome (AIDS). Science, 220(4599), 868-871.
- Branson, B. M., Owen, S. M., Wesolowski, L., Bennett, B., Werner, B. G., & Wroblewski, K. E. (2014). Laboratory testing for the diagnosis of HIV infection: Updated recommendations. Centers for Disease Control and Prevention.
- Clavel, F., Guétard, D., Brun-Vézinet, F., Chamaret, S., Rey, M. A., Santos-Ferreira, M. O., … & Montagnier, L. (1986). Isolation of a new human retrovirus from West African patients with AIDS. Science, 233(4761), 343-346.
- Fiebig, E. W., Wright, D. J., Rawal, B. D., Garrett, P. E., Schumacher, R. T., Peddada, L., … & Busch, M. P. (2003). Dynamics of HIV viremia and antibody seroconversion in plasma donors: Implications for diagnosis and staging of primary HIV infection. AIDS, 17(13), 1871-1879.
- Ghosn, J., Taiwo, B., Seedat, S., Autran, B., & Katlama, C. (2018). HIV. The Lancet, 392(10148), 685-697.