By Susan Milius
Comb jellies may look like little more than filmy ghosts twinkling in the sea. Yet their immune systems can tell whether the jellies have encountered certain bacteria before.
Biologists once thought only vertebrates could recognize a familiar foe and tailor an immune response to it, says Sören Bolte of the University of Kiel in Germany. But insects and crustaceans turn out to have their own ways of accomplishing the same memorylike task.
Now, plunging further down to the ancient branches at the base of animals’ genealogical tree, Bolte and his colleagues report similar immune-system abilities in the comb jelly Mnemiopsis leidyi. Four probable immune-reaction genes behaved differently the second time they encountered harmful bacteria, Bolte and his colleagues say November 19 in Biology Letters. The first bacterial assault “primed” the jelly immune system to react differently during the second attack, he says.