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Primitive Stage of White Cells Discovered in FishesThis evolutionary link could be beneficial for human health and pisciculture |
By Stefan Anitei, Science Editor
29th of September 2006, 09:30 GMT
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A primitive version of B cells of the mammal immune system has been discovered in fish by a team from the University of Pennsylvania School of Veterinary Medicine.
In mammals, B cells produce antibodies to fight infection but in fish, scientists found that B cells realize phagocytosis ( "cell eating" ), the process by which cells of the immune system ingest and digest foreign particles and microbes.
B cells were first discovered in chickens in the 1960s.
The finding designs an evolutionary pattern from primitive fish to mammal's immune system and offers a potential new strategy for developing much-needed fish vaccines.
"When examining fish B cells we see them actively attacking and eating foreign bodies, which is a behavior that, according to the current dogma, just shouldn't happen in B cells," said J. Oriol Sunyer,
a professor in Penn Vet's Department of Pathobiology.
"I believe it is evidence for a very real connection between the most primitive forms of immunological defense, which has survived in fish, and the more advanced, adaptive immune response seen in humans and other mammals."
About 400 million years ago, the earliest ancestors of modern fish split off of the evolutionary pathway that became the earliest tetrapods (four legged vertebrates) which later led to mammals.
In mammals, the B cells chiefly create antibodies that destroy foreign particles and microbes.
Phagocytic cells in mammals are few and apart from the complex interactions that drive other white blood cells.
The unsuspected B cells activity in fish was detected while examining the immune cells of rainbow trout and catfish.
These B cells account for more than 30-40% of all immune cells in fish, while phagocytic cells in mammals account to a much smaller percentage.
Further researches proved that amphibians retain a significant digestive power in their B cells.
"The immune systems of amphibians and fish are far less advanced than ours," Sunyer said.
"When you only have a rudimentary adaptive immune system, it helps to have more phagocytic cells to compensate, which is what has served fish so well over the last 400 million years."
Primitive immune systems are critical to discover and understand immune responses in humans and other mammals.
"At this point, we cannot rule out the possibility that small subpopulations of phagocytic B cells, perhaps remnants of those present in fish, are still present in mammals," Sunyer said.
These findings have implications in pisciculture.
This research has proved that adaptive immune system in fish plays a smaller part of the overall fish immune system than previously thought.
So, the current vaccines given to farmed salmons are less effective than desired.
"If we work to create vaccines that encourage phagocytic B cell to respond to infection, then we would play to the strengths of fish immunity," Sunyer said.
"In the long term, farming is a better, more environmentally sound approach to fishing, so better vaccines may make the practice more financially attractive to fisherman and less destructive to fish populations."
"Here we have a clear picture of where one part of the immune system, primitive phagocytes, adapted over time to serve a more complex role as part of the immune system that humans enjoy today," Sunyer said.
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