By Bill Schutt – Big Think
The crabs’ blue blood contains an ancient immune defense mechanism that has helped save countless human lives.
The story of the Atlantic horseshoe crab’s first turn toward medical relevance occurred in 1956. That’s when Woods Hole pathobiologist Fred Bang determined that certain types of bacteria caused horseshoe crab blood to clot into stringy masses. He and his colleagues hypothesized that this was an ancient form of immune defense. Eventually, they determined that a type of blood cell called an amoebocyte was responsible for the clot formation. As their name implies, amoebocytes resemble amoebas, the blobby single-celled protists that make pseudopods so popular and dysentery so unpopular.
>Bang, and those who followed up his research, hypothesized that the clotting ability of the amoebocyte evolved in response to the bacteria-and-pathogen-rich muck that horseshoe crabs plow through for pretty much their entire lives. Their army of blood-borne amoebocytes can wall off foreign invaders, isolating them in prisons of gelatinous goo before they can spread their infections.