What makes horseshoe crab blood special? How does it differ so much from mammals and even other fish? Join MBL Veterinarian Lisa Abbo to take a deep dive into the circulatory system and special blood of the American Horseshoe Crab (Limulus polyphemus) in the latest #MBLSciShoot digital learning lesson.

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Related Reading

Species: Horseshoe Crab | Atlantic State Marine Fisheries Commission

Hooray for Horseshoe Crabs Teaching Guide (PDF) | Estuaries 101 Curriculum

An introduction to immunology and immunopathology | Allergy, Asthma & Clinical Immunology

Horseshoe Crab Anatomy | Maryland Department of Natural Resources

The Role of Horseshoe Crabs in the Biomedical Industry and Recent Trends Impacting Species Sustainability | Frontiers in Marine Science 

Questions from the Audience

Are there any other animals we know of that use hemocyanin to carry oxygen through their blood? And are those animals related to horseshoe crabs evolutionarily?

Yes! Other arthropods like spiders and scorpions which are related to horseshoe crabs (phylum Arthropoda), some mollusks like octopuses and cuttlefish, crustaceans like crabs (also in the phylum Arthropoda). These are all invertebrates. There are at least two other oxygen-carrying molecules in other animals such as chlorocruorin and hemerythrin in marine worms.

When did scientists start experimenting / studying the horseshoe crabs for biomedical purposes?

Fred Bang, in 1956, was the first to describe the observation that HSC blood clots in the presence of gram-negative bacteria. Soon other researchers began working with horseshoe crabs and in 1977, LAL became FDA approved for used to test biologics. There is a link to a great article that includes some of the history in one of the answers to another question below.

You talked about the Atlantic horseshoe crab, but I'm wondering if all four species of horseshoe crabs have the same type of blood and are they all used for research or just the Atlantic?

Yes, they all have the same type of blood and the species Tachypleus gigus a species native to Asia is harvested in the same manner as Limulus polyphemus is here in the U.S.; the difference is that instead of Limulus Amoebocyte Lysate (LAL), the product is called TAL Tachypleus Amoebocyte Lysate (TAL). Here is a great article all about it from The Atlantic.

hello! Fantastic video! Do you know anything about the process of the synthetic recombinant factor C (LAL substitute). I guess in comparison to how the cell granulates and coagulates in horseshoe crab blood?

My understanding is that Factor C is the crucial first step in the clotting cascade and this is the molecule that researchers are targeting when creating synthetic LAL. When stimulated by the presence of LPS this synthetic molecule cleaves a fluorescent substrate which can then be quantified and give a result ie. whether or not the substance being tested is contaminated with LPS (dangerous bacteria). Based on a review paper there are several different forms of synthetic Factor C that have been tested and most/all appear to be at least equivalent to real LAL in their ability to detect LPS. The reason this synthetic form has not replaced real LAL is likely complicated but at least part of the reason is resistance to change the protocol when human lives are literally at stake so the risk might be too high for a pharmaceutical company. As patents expire and the cost to produce this synthetic form drops this will likely create a market for the product and hopefully become widespread.

Watch the rest of the MBLSciShoot videos on our Youtube channel.