How does your body spot a cell that a virus has secretly taken over?
Two scientists found the answer by infecting mice with a meningitis virus, and won a Nobel Prize for discovering your cells wear an ID tag.
▶ Start the storyNearly every cell in your body constantly displays tiny fragments of its own proteins on its surface, like a running photo ID, using molecules called MHC class I. If a virus infects the cell and forces it to make viral proteins, fragments of those viral proteins get displayed too. A killer T cell patrolling nearby checks that display. If it recognizes a viral fragment riding on an MHC molecule, it destroys the infected cell on the spot.
Step 1: Virus hides inside
It forces the cell to make viral proteins
Step 2: MHC displays fragments
Pieces of those proteins reach the cell surface
Step 3: T cell checks the ID
Its receptor scans for a matching viral fragment
Step 4: Double match required
Viral fragment + self MHC, together, on the same cell
Step 5: Cell destroyed
The killer T cell eliminates the infected cell
Scientists already knew MHC molecules existed, because they are what makes organ transplants succeed or fail: the immune system rejects tissue from a badly mismatched donor. But working with mice infected by a meningitis virus in the 1970s, Peter Doherty and Rolf Zinkernagel found something stranger. A killer T cell only recognized an infected cell when it detected the viral fragment and a matching self MHC molecule at the same time, never either alone. The discovery won them the 1996 Nobel Prize in Physiology or Medicine.
The same ID system is why transplants need compatible donors. The human version of MHC, called HLA, comes in more than 17,000 known variants, so it is extremely uncommon for any two unrelated people to carry identical copies.
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Recap
A killer T cell destroys a cell only when it recognizes both a foreign fragment and a matching self MHC molecule displayed together on that cell's surface.
Surprising fact · Doherty and Zinkernagel showed a killer T cell needs to detect a viral fragment and a matching self MHC molecule on the same cell at once, work that won the 1996 Nobel Prize.
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No source, no claim. Every fact in this lesson (13 claims) cites at least one of these.