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Pesticide Chemical Leaves Immune System Helpless

Lab study shows crop chemical debilitates human killer cells

MONDAY, April 8 , 2002 (HealthDayNews) -- An hour's exposure to a commonly used crop pesticide could render your immune system defenseless.

That's the disturbing finding of a new laboratory study presented today at the annual meeting of the American Chemical Society in Orlando, Fla.

The research, conducted at Tennessee State University, found an ingredient commonly found in a fungicide used to protect potato, pecan and sugar beet crops and in a pesticide used to control Colorado potato beetles could cause irreversible damage to human killer cells -- the immune system's first line of defense against cancer and viruses.

"Our study showed that, at least in laboratory tests, natural killer cells that were exposed to the chemical compound Triphenyltin (TPT) were rendered almost totally helpless within hours after exposure," says chemistry professor Margaret Whelan, who oversaw the research.

The research was the first to demonstrate the effect in human blood cells, and she adds the findings are cause for concern.

"We only exposed these immune cells to TPT for a short period of time, and within one hour we saw a reduction in their ability to defend the body," Whelan says.

Even after the immune cells were removed from the TPT and left to rest in a clean environment for six days, they couldn't recover from the chemical assault, she adds.

"In fact, the cells grew weaker after six days and were less able to fight cancer cells then they were an hour or two after the initial exposure," she says.

For occupational and environmental medicine specialist Dr. Jacqueline Moline, the study is perhaps an omen.

"It is hard to say if what was found in the laboratory studies would also be found in humans working with this substance, but it certainly is a finding that should not be ignored, and must be pursued further," says Moline, an associate professor of occupational and environmental medicine at Mount Sinai School of Medicine.

The next step, Moline says, should be an animal study and, eventually, a human study of agricultural workers exposed to TPT on a regular basis.

Whelan says this is precisely the plan they have in mind.

"We also want to look into whether TPT can have a cumulative effect in the body, which will tell us if short exposures, over time, can also have a detrimental effect on the immune system," she says.

The study involved exposing human immune system "killer" cells to concentrations of TPT at a level just moderately higher than what an agricultural worker might be exposed to in the field. The otherwise healthy immune cells were exposed to the TPT for just one hour. They were then removed, and placed in a TPT-free environment to recover.

To test their ability to defend, the immune system cells were then exposed to human leukemia cells. A simple chemical compound let researchers tell whether the immune cells fought off the leukemia cells.

After one hour, Whelan says the immune cells lost 50 percent to 60 percent of their tumor-fighting power. By the time six days had passed, their strength deteriorated further, down 84 percent.

"These cells were pretty much useless to defend the body," Whelan says. Despite the fact that they had been away from the TPT for six days, the immune cells couldn't destroy any leukemia cells.

"The damage appeared to be permanent," Whelan says.

Moline notes this is an important factor, but it may or may not be duplicated in the human body.

"The immune system is a very complex network, and while the study offers some important information to consider, we don't know at this point if what was found in the lab would be duplicated in the human body with equal exposure levels," Moline says.

Although both Whelan and Moline say that there is probably little concern right now for those who may eat crops dusted with TPT, they also say that could change once workers are tested.

"If we find the same kind of impairment in the immune cells of agricultural workers exposed to TPT, then we'll have to look towards whether or not this chemical can accumulate in the body," Whelan says.

What To Do

For more information on the immune system functions, visit The Seattle Treatment Education Project .

To learn more about the effects of pesticides on health, check out

SOURCES: Margaret Whelan, Ph.D., professor, chemistry, Tennessee State University, Nashville, Tenn.; Jacqueline Moline, M.D., associate professor, occupational and environmental medicine, Mount Sinai School of Medicine, New York City; April 8, 2002, study presentation, American Chemical Society annual meeting, Orlando, Fla.
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