Blue Blood Donors of the Sea
January 3, 2012 § Leave a comment
While shooting lab photos at the University of Oslo’s Department of Medical Biochemistry, I came across this little guy – an atlantic horseshoe crab kept in a desiccator. What was this odd-looking sea creature doing in a hospital research lab?
One of the lab technicians told me the fascinating story of the medical contribution of this living fossil. More closely related to scorpions and spiders than crabs, the atlantic horseshoe crab is most common along the east coast of North America and in the Gulf of Mexico. The horseshoe name comes from the shape of the animal’s carapace. In Norway we call them “dolkhale”, which translates as “daggertail”, from the long pointy tail.
While doing research on blood circulation using the Atlantic horseshoe crab in the 1950s, Frederick B. Bang MD at Johns Hopkins University found that the injection of certain bacteria into the crab’s blood stream resulted in massive clotting of the blood (his original paper from 1956 can be found here). Further research showed that the clotting reaction was only produced by gram-negative bacteria and that the reaction was also produced when dead bacteria were injected. Joined by hematologist Jack Levin, Bang continued his research into the clotting and found that it was produced by endotoxins, toxins found in the membrane of gram-negative bacteria.
As was the case, endotoxins were a big problem for the medical industry. Endotoxins can cause severe immune reactions in humans, and the toxins are still present when the bacteria itself has been killed. So sterilizing injectable medicines, IV fluids, surgical instruments etc. will not eradicate the endotoxins. Bang and Levin realized that the horseshoe crab blood, which clots in the presence of endotoxins could be used to detect the toxin. Together they developed the Limulus Amebocyte Lysate (LAL) test.
The horseshoe crab don’t have an immune system, but have developed a defense against the gram-negative bacteria which saturates the shallow waters where the crab live. When the blood cells (amebocytes) detect the presence of endotoxins they release granules containing a clotting agent. A clot forms and encapsulates any bacteria in that area. If the bacteria entered through a wound the clot also acts as a barrier to the outside until the wound is healed. Unlike mammals, the horseshoe crab’s blood has a copper-containing protein as an oxygen carrier, and their blood turns a milky blue when oxygenated. To make the LAL test, blood is collected from living horseshoe crabs which are released back into the sea after the procedure. The amebocytes are isolated from the blood serum and mixed with distilled water. The water causes the cells to burst (lysis) and the clotting agent inside the cells is released. When substance to be tested is added to this solution the clotting will occur even if as little as one part per trillion endotoxin is present.
Here is a short clip from PBS which shows how the blood collection is done:
The specimen at the lab was quite small and not an adult it would seem. They told me it had been at the lab since the 80s, probably brought home by someone who visited a LAL test manufacturer as a curiosity. It was not kept in the desiccator to keep it dry. I just think it seemed like a nice display jar.
Fascinating story and a fascinating animal!