|Systematic viral epitope scanning (VirScan). The color of |
each cell in the heatmap depicts the relative number of
antigenic epitopes detected for a virus (rows) in each
sample (columns). (Credit: Xu et al., 2015).
New technology makes it possible to test for current and past infections with any known human virus by analyzing a single drop of a person's blood. The method, called VirScan, is an efficient alternative to existing diagnostics that test for specific viruses one at a time. The scientists described the new technology in the journal Science.
With VirScan, scientists can run a single test to determine which viruses have infected an individual, rather than limiting their analysis to particular viruses. That unbiased approach could uncover unexpected factors affecting individual patients' health, and also expands opportunities to analyze and compare viral infections in large populations. The comprehensive analysis can be performed for about $25 per blood sample.
VirScan works by screening the blood for antibodies against any of the 206 species of viruses known to infect humans. The immune system ramps up production of pathogen-specific antibodies when it encounters a virus for the first time, and it can continue to produce those antibodies for years or decades after it clears an infection. That means VirScan not only identifies viral infections that the immune system is actively fighting, but also provides a history of an individual's past infections.
To develop the new test, the researchers synthesized more than 93,000 short pieces of DNA encoding different segments of viral proteins. They introduced those pieces of DNA into bacteria-infecting viruses called bacteriophage. Each bacteriophage manufactured one of the protein segments - known as a peptide - and displayed the peptide on its surface. As a group, the bacteriophage displayed all of the protein sequences found in the more than 1,000 known strains of human viruses.
Antibodies in the blood find their viral targets by recognizing unique features known as epitopes that are embedded in proteins on the virus surface. To perform the VirScan analysis, all of the peptide-displaying bacteriophage are allowed to mingle with a blood sample. Antiviral antibodies in the blood find and bind to their target epitopes within the displayed peptides. The scientists then retrieve the antibodies and wash away everything except for the few bacteriophage that cling to them. By sequencing the DNA of those bacteriophage, they can identify which viral protein pieces were grabbed onto by antibodies in the blood sample. That tells the scientists which viruses a person's immune system has previously encountered, either through infection or through vaccination. The researchers estimate it would take about 2-3 days to process 100 samples, assuming sequencing is working optimally. However, this speed is likely to increase with further development.
To test the method, the team used it to analyze blood samples from 569 people from four countries, examining about 100 million potential antibody/epitope interactions. They found that on average, each person had antibodies to ten different species of viruses. As expected, antibodies against certain viruses were common among adults but not in children, suggesting that children had not yet been exposed to those viruses. Individuals residing South Africa, Peru, and Thailand, tended to have antibodies against more viruses than people in the United States. The researchers also found that people infected with HIV had antibodies against many more viruses than did people without HIV.
The researchers believe the developed approach is not limited to antiviral antibodies. They are also using it to look for antibodies that attack a body's own tissue in certain autoimmune diseases that are associated with cancer. A similar approach could also be used to screen for antibodies against other types of pathogens.
Based on material originally posted by Howard Hughes Medical Institute.