Monday, June 8, 2009

Horseshoe crab and LAL (II)

In continuation from my first posting, this second one will cover about the discovery of horseshoe crab's blood and their eventual commercialisation.

Scientists have been studying the properties of blood clotting of the horseshoe crab more than a century ago. However, it was only during the 1950s when Fred Bang discovered in that blood from Limulus polyphemus clot when bacteria was present, even dead ones. Eventually, it was recognised that it was due to a mobile blood cell called ameobocyte.

These cells possess lots of granules which will release clotting factors and other antimicrobial molecules in response to external stimulus. Besides this, many agglutinins are also present in the blood stream to as an additional protection. This is probably the reason why these living fossils have managed to survive on Earth for millions of years.

It was eventually found out that endotoxins found on gram-negative bacteria causes the clotting in the horseshoe crab's blood. They managed to devise a method to isolate these chemicals by centrifuging the blood to separate the ameobocytes and placing them in water causing them to lyse or burst. The resulting liquid is known as LAL or Limulus Ameobocyte Lysate.

So sensitive and thus effective is the LAL in detecting endotoxins that the Food and Drug Administration (FDA) replaced this from the standard rabbit test. Unfortunately, at that time, the only way to obtain LAL was to harvest live horseshoe crabs and gave them a forced blood donation. They were then returned to the sea (if they managed to survive the process). But studies had shown that mortailty was low.

Another species of horseshoe, Tachypleus gigas found locally

A leap in scientific advancement but unfortunately, not much in terms of ethics. I guess most would prefer horseshoe crabs suffering instead of rabbits due to the "Bambi syndrome" (in simple terms, just being cute and cuddly) but it would not be if you see this picture. To me, it is no different from catching bears to extract their bile which is condemned by many.

Check out my other postings in this series:
Part I: Horseshoe crabs and Endotoxin
Part III: Horseshoe crabs and Factor C (to be updated)

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