HIV testing: 5 ways to take action

When it comes to AIDS, many people feel terrified, fearing that they will be infected. Facts have proved that AIDS is widely transmitted, especially sexually transmitted, so once you find yourself feeling unwell, you must get tested in time. Currently, the most common AIDS testing methods include antibody testing, antigen testing, enzyme-linked immunosorbent assay, immunoblot test, immunofluorescence test (IFA), etc.

1. Antibody and antigen detection

HIV antibodies generally appear gradually a few weeks after human infection and can last a lifetime. Serological tests are divided into screening and confirmation tests. The most commonly used screening test and confirmatory test are ELISA and Western blot (WB), respectively. Conventional experimental methods: enzyme-linked immunosorbent assay, Western blot, and indirect immunofluorescence assay (IFA). Rapid detection methods: gelatin particle agglutination test, dot immunobinding test, P24 antigen detection, molecular biology method, RT?PCR detection method, fluorescent real-time PCR detection technology, branched DNA (bDNA), ligase chain reaction (LCR), nucleic acid sequence-dependent amplification (NASBA), transcription-mediated amplification (TMA)

2. Enzyme-linked immunosorbent assay

The basic principle of ELISA is that immune reactants form enzyme conjugates through chemical or immunological methods. The enzyme conjugates can combine with the corresponding antigens or antibodies in the sample to be tested to form immune complexes. Then the enzyme substrate is added. After the catalysis or hydrolysis of the enzyme, the colorless substrate produces color, and the results are observed with the naked eye or a spectrophotometer. The HIV ELISA reagents used for initial screening have now developed into the fourth generation of detection reagents. The first generation of reagents mainly used viral lysates or partially purified viral antigens to coat reaction plates to detect antibodies in serum. Since the coated antigen is not very pure, the false positive rate is high. The second-generation reagents use recombinant antigens and synthetic peptides obtained by genetic engineering methods to coat the reaction plates. Due to the use of purified antigens, the specificity has been greatly improved. The third-generation reagent uses a double antigen sandwich method to detect antibodies, further improving sensitivity. The fourth-generation reagent further adds the detection of P24 antigen based on the third-generation reagent. HIV antigen and anti-P24 antibody are coated on the reaction plate at the same time, and HIV antibody and P24 antigen in serum can be detected at the same time.

3. Immunoblotting

The immunoblotting test is mainly used for confirmation tests. The basic principle is that the whole HIV virus antigen is subjected to SDS-PAGE electrophoresis to separate protein bands of different molecular weights, and then these separated different protein bands are transferred to the nitrocellulose membrane. The membrane is cut into strips, and each strip of nitrocellulose membrane contains HIV virus antigens separated by electrophoresis. The serum sample to be tested is diluted to 1/100 with diluent, and then added directly to the nitrocellulose membrane and shaken at a constant temperature to allow it to fully contact and react. If the serum contains anti-HIV antibodies, it will combine with the antigen band on the membrane strip. After adding anti-human IgG enzyme conjugate and substrate, the reactive antigen-antibody binding band will appear purple-brown, and the result can be determined based on the appearance of the bands. It has been reported that the specificity of the immunoblot test is not very good, with a false positive rate of about 2%, but the immunoblot test is still the most commonly used HIV confirmation test.

4. Immunofluorescence assay (IFA)

The basic principle is to use H?9 or HUT?78 cultured cells as carriers, infect the cells with HIV, and the cells will contain HIV antigens. The HIV-infected lymphocytes are smeared on a glass slide, fixed, and prepared as antigen slices. The serum to be tested is added, and the anti-HIV antibodies in the serum to be tested combine with the antigens and then with fluorescein-labeled anti-human Ig. Yellow-green fluorescence can be seen in the cells under a fluorescence microscope.

5. Gelatin particle agglutination test (PA)

The basic process of PA is to dilute the sample first, then add antigen-sensitized and non-sensitized gelatin particles respectively, mix well and keep warm (usually at room temperature). When HIV antibodies are present in the serum, the antigen-sensitized gelatin particles react with the antibodies, and the results are judged based on the agglutination of the gelatin particles in the wells. PA is easy to operate, does not require special instruments or equipment, and is suitable for testing small amounts of specimens.