The adaptive immune system, which can recognize, attack, and remember potentially harmful microbes, may have appeared on the evolutionary scene millions of years earlier than scientists thought. The immune system of the sea lamprey, a primitive, jawless fish, contains two cell types that recognize and respond to characteristic molecules associated with invading pathogens, researchers report in this week's __Nature__. "It's amazing to us," lead author linkurl:Max Cooper,; an immunologist at Emory University in Atlanta, told __The Scientist__. "We never anticipated it."
The lamprey's imposing (but jawless) mouth
Image: US Environmental Protection Agency
Organisms such as plants and invertebrates have innate immune systems, which protect against pathogens in a nonspecific manner. More highly derived organisms such as mammals, however, also have adaptive immune systems, which can mount a two-pronged attack against foreign invaders. Adaptive immunity consists of humoral defenses, where B lymphocytes secrete antibodies against specific antigens, and cellular defenses, in...

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