Virus hides inside cloak of invisibility

2019-02-28 01:05:11

By Peter Aldhous ARE you an Epstein-Barr virus carrier? The answer is probably yes, as more than 90 per cent of us carry EBV throughout most of our lives. Now researchers in Sweden and the US have discovered how EBV is able to survive in our bodies for so long. The main protein made by EBV, they say, contains an amino acid sequence which protects it from exposure to the immune system. When a virus infects one of our cells, fragments of its proteins are transported to the cell’s surface. “Each cell bears on its surface a fingerprint of whatever is contained inside,” says Maria Masucci of the Karolinska Institute in Stockholm, who led the new research. When the immune system’s killer T cells confront an invading virus’s proteins, they destroy infected cells. In the case of EBV, however, this “antigen presentation” system breaks down: most of the time, EBV makes just one protein, called EBNA1, which killer cells cannot detect. The cloak of secrecy is lifted only when EBV causes glandular fever – when it produces several other proteins which do trigger an immune response. Masucci suspected that EBNA1’s invisibility was linked to an unusual sequence of alternating glycine and alanine amino acids, the length of which varies from 70 to 300 amino acids. To test the theory, her team genetically engineered vaccinia viruses to make altered EBV proteins. The researchers created vaccinia viruses which made hybrid proteins containing parts of EBNA1, and parts of one of the glandular fever proteins. Cultured human cells infected with these viruses were quickly targeted by the appropriate killer cells if the hybrid proteins lacked the repeating sequence. Those containing the glycine-alanine sequence, however, remained unnoticed (Nature, vol 375,