NEXT time you cut yourself, spare a thought for the suicidal white blood
cells which sacrifice themselves to save you from invading bacteria. By
self-destructing, these suicidal macrophages can quickly release large amounts
of the alarm chemicals that summon reinforcements from the immune system.
The puzzle for immunologists has been how the macrophages identify invaders.
The secret, say Arturo Zychlinsky and his colleagues at the New York University
School of Medicine, is lipoproteins鈥攖he fatty proteins found on the
surface of almost all bacteria.
Zychlinsky exposed macrophages to bacterial lipoproteins and discovered that
the immune cells have a 鈥渄eath receptor鈥� that recognises lipoproteins. When
these bind to the receptor, a suicide order is instantly issued within the cell
and triggers programmed cell death, or apoptosis.
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The death receptor, 鈥淭oll-like receptor-2鈥�, doesn鈥檛 resemble other apoptosis
triggers, such as tumour necrosis factor receptor and a receptor called fas.
These involve several intermediate signals before the cell self-destructs. The
newly discovered death receptor provides a short cut to suicide, speeding up
inflammation before the bacteria can gain a foothold.