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Virally infected cells are detected and eliminated from the body by CD8+ T cells using a receptor called the TCR (the T cell receptor for antigen). Detection of the virally infected cell relies on specialized proteins like MHC class I that display viral proteins on the surface of infected cells. This 'flags down' the passing killer T cells for the kill, by identifying the infected cell as an appropriate target. Some viruses are extremely clever, however, and attempt to avoid detection through elaborate subterfuges. Cytomegalovirus (CMV), for example, is a virus that disrupts the production of class I to evade being killed by T cells.
In the March issue of Nature Immunology Nature Immunology (Vol. 2, No. 3), Spies and colleagues have discovered how T cells can detect CMV-infected cells even if they have little class I. CD8+ T cells express another receptor, called NKG2D, that binds to a protein called MIC. MIC is not normally found on most cells. However, when CMV infects cells, it causes the cell to make MIC, which is then expressed on the cell surface. The interaction between NKG2D and MIC 'kick starts' the T cell into action by energizing it to destroy the virally infected cell. A promising new direction for viral research will be investigating whether this strategy applies to the detection of all virally infected cells or is specific for the detection of CMV.
A News & Views was written on this paper by Eric Vivier of Marseille, France.
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Message posted by: Trevor M. D'Souza