IN THE MAGAZINE

OLDER THAN COELACANTHS

Trilobites and Their Endotoxic Reagent

The horseshoe crab is as old as the dinosaurs. Its blood is an essential ingredient in everyday medicine, and yet we know so little about it.

The horseshoe crab, or Limulus Arthro-podus, is a living cousin of the trilobite, a marine arthropod that scuttled across the Paleozoic seabeds some 570 to 245 million years ago. Each year, it spawns during the first full and new moon of spring from the Yucatan to Maine, but most heavily in Delaware Bay, where thousands come ashore in a primitive orgy of procreation that makes the bay’s shore look like a wet cobbled street at night.

But horseshoe crabs are of interest to more than just paleontologists and nocturnal beach-walkers. Some 250,000 of them are collected each year for use by the pharmaceutical industry. Their blood is used to make LAL, a reagent used to test for endotoxins, which can induce septic shock, a condition that is fatal in over 50 percent of patients.

So why use horseshoe crab blood?

Horseshoe crabs are so ancient they lack antibodies in their blood. When endotoxins, which are created by bacteria omnipresent in seawater, enter a horseshoe crab’s bloodstream, its blood clots, keeping out bacteria, toxins, and anything else that might invade.

LAL, when employed to test batches of IV/immunization drugs, uses this clotting property to quickly detect the presence of endotoxins. An effective, simple, and relatively cheap way of avoiding toxic shock, blah blah blah, endotoxin, yadda, yadda, crab, crab, crab... anyhoooo.

LAUREL MAURY
We first saw this in the March 2002 issue of The Ecologist (Vol. 32, No. 10, theecologist.org) but couldn’t get through it.

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