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Horseshoe crab blood clots at the faintest trace of toxins from bacteria. Since the 1970s an extract of it, called LAL, has been used to check that injectable medicines and implants are free of them.

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The story behind the card

Horseshoe crabs are not true crabs; they are closer relatives of spiders and scorpions. Their blood is blue because it carries oxygen with haemocyanin, a copper-based molecule. In 1956 the American scientist Frederik Bang found that bacteria make the blood gel. The toxins behind this, endotoxins, are fragments of the outer wall of certain bacteria and can cause dangerous fevers in the bloodstream. LAL stands for Limulus amebocyte lysate, an extract of the crab's blood cells; the United States approved it in 1977. Collecting it means bleeding wild crabs, and studies suggest up to about 30 per cent may die afterwards. A synthetic alternative, recombinant factor C, has been sold since 2003 and was accepted in the official rulebooks for medicine testing, the European Pharmacopoeia in 2016 and the US Pharmacopeia in 2025.

Türkçe oku
Nal yengecinin kanı, bakterilerden kalan zehirli maddelerin en küçük izinde bile pıhtılaşır. 1970'lerden beri bu kandan elde edilen LAL adlı özüt, iğneyle verilen ilaçların ve tıbbi implantların bu maddeleri içermediğini doğrulamak için kullanılır.

Nal yengeçleri aslında gerçek yengeç değildir; örümceklere ve akreplere daha yakındırlar. Kanları mavidir, çünkü oksijeni bakır içeren hemosiyanin adlı bir molekülle taşır. 1956'da Amerikalı bilim insanı Frederik Bang, bakterilerin bu kanı jöle gibi pıhtılaştırdığını keşfetti. Buna yol açan endotoksinler, bazı bakterilerin dış zarından kopan parçalardır ve kana karışırsa tehlikeli ateşe yol açabilir. LAL, Limulus amebocyte lysate'in kısaltmasıdır ve yengecin kan hücrelerinden elde edilen özüt demektir; ABD'de 1977'de onaylandı. Bunun için yabani yengeçlerin kanı alınıyor ve araştırmalara göre bu yengeçlerin yüzde 30 kadarı sonradan ölebiliyor. Rekombinant faktör C adlı yapay bir alternatif 2003'ten beri satılıyor; ilaç testlerinin kurallarını belirleyen resmî kitaplardan Avrupa Farmakopesi onu 2016'da, ABD Farmakopesi de 2025'te kabul etti.

Sources and further reading

Background reading: Limulus amebocyte lysate
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