[media-credit name=”photo courtesy of UCSB.edu” align=”alignleft” width=”152″][/media-credit]

The species of sea squirt, also known as the tunicate, is a model system for researchers due to its rapid rejection of foreign colonies.

Researchers at UCSB suggest that further study into the natural transplantation process of the sea squirt species Botryllus schlosseri could provide crucial insight into how to avoid transplant rejection in human patients.


The Botryllus schlosseri — which bears a common vertebrate ancestor with homo sapiens — allowed the team to study organ rejection on a much simpler scale than seen in the human body. UCSB assistant biology professor Anthony De Tomaso, who led the study, said the small organism could help medical researchers better understand how to counter organ and bone marrow rejection.

“If you think of the decision process like an engine, we are studying a Model T and humans are Ferraris,” De Tomaso, who has studied sea squirts’ transplantation processes for 15 years, said. “The concept is the same but the Ferrari has a lot more bells and whistles — if you want to learn how the engine works, you want to start on something simple.”

Although the small animal starts its life as a mobile organism comparable to a tadpole, it usually fuses itself to other schlosseri then eventually attaches itself onto other intertidal surfaces and remains stationary. De Tomaso said the sea squirt performs the process of deciding whether to accept or reject fellow organisms in less than a day, which allowed his team to design experiments with high turnaround. By studying the organism’s decision-making process, the scientists hope to better understand the mechanism in larger animals.

According to De Tomaso, less than one in 10,000 donors match transplant patients, excluding donors who are family members. And, if a patient’s body declines an organ transplant, the recipient must take immunosuppressive drugs for the remainder of their life to suppress his or her own immune system from attacking the foreign organ. Suppression of the immune system is dangerous for the organism, since it opens it up to attack from pathogens. If the rejection response was able to be controlled, organ transplants — in theory — could be performed between any two people since the body could be instructed to accept the transplanted organ rather than reject it. Tomaso said there are currently 110,000 people in the United States listed as requiring organ transplants.

If research proves favorable, Tomaso said knowledge of the sea squirt’s mechanism could combat fatal cases of human organ failure.

“We would have a powerful new tool in the fight against leukemia,” De Tomaso said. “We could just kill the host’s bone marrow and then transplant new stem cells.”