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Other experiments have been made to see if sharks could do this. The Mote Marine Laboratory designed experiments to see whether tumors could be induced in the sharks and skates by exposing them to potent carcinogenic, which are cancer-causing chemicals. They did this by placing the chemicals in their food or surrounding tank water, or by direct injection into their muscle. They then monitored subsequent pathways of metabolism or detoxification of the carcinogens in the test animals. While there were similarities and differences in the responses when compared with mammals, no changes in the target tissues or their genetic material ever resulted in cancerous tumor formation in the sharks or skates. The conclusions were that the immune system of sharks probably plays a vital role in the overall health of these animals. But there are some important differences between the immune arsenals of mammals and sharks. The immune system of mammals typically consists of two parts, which utilize a variety of immune cells as well as several classes of proteins called immunoglobulins (antibodies). One interesting thing that the MML points out is the differences in how sharks lack a bony skeleton and do not have bone marrow. Typically the immune cells are produced and mature in the bone marrow and these cells are mobilized to the bloodstream to fight invading substances. But in sharks, the immune cells are produced in the spleen, thymus and unique tissues associated with the epigonal organ (gonads) and Leydig organ (esophagus). Their studies have determined that a “significant number of immune cells in these animals actually mature as they circulate in the bloodstream.” The immune cells already in the shark's blood may be available to respond without a lag period, resulting in a more efficient immune response which gives a higher chance of fighting off foreign invaders. |
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