Horseshoe crabs don't have immune systems like we do. They don't produce antibodies to fight off infection. Instead, they rely on the chemistry of their blue blood. It contains limulus amebocyte lysate (LAL), which inactivates bacterial endotoxins. This compound is used in the pharmaceutical industry to test vaccines, drugs, and medical devices.
Every year, American biomedical companies harvest a half-million horseshoe crabs to harvest their blood. They don't take all the blood, and they return the crabs to the sea, but still about 30% of them die from the experience. Also, by missing mating season, these crabs will not produce 80,000 eggs each, which not only reduces their descendants but also deprives seabirds of their normal diet of crab eggs.
In the Delaware Bay, the horseshoe crab population is only 25% of what it was in 1990. Fortunately, scientists have developed an artificial substitute for LAL, recombinant Factor C (rFC), that performs just as well for human drug testing. Unfortunately, while rFC is used in China and the European Union, it has yet to be approved for use in the US. Read about the efforts to save both horseshoe crabs and develop new drugs and vaccines at The Verge.
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