Immune System Could Be Rendered Irreversibly Powerless.American Chemical Society News Release Posted Tuesday, July 23, 2002 by ctustis
ORLANDO, FL -- Natural killer cells are like the Marines of our immune
system; they have the capability to defend us against a lot of different
threats. But researchers have uncovered a potential counter-threat to
this front-line protection. Our body‚s natural killer cells could be
rendered irreversibly powerless to guard against invading tumors and
viral onslaughts after only a brief exposure to a compound found in some
agricultural pesticides and fungicides.
The findings were presented at the 223rd national meeting of the American
Chemical Society (ACS), the world‚s largest scientific society.

Triphenyltin (TPT) is a compound used in fungicides to protect pecan,
potato and sugar beet crops and in pesticides to guard against Colorado
potato beetles. In tests at Tennessee State University in Nashville, TN,
researchers have found an apparent irreversible inhibition of natural
killer cell function after as little as a one-hour exposure to TPT.

The laboratory tests were the first to ever examine TPT specifically in
human natural killer cells, according to chemistry professor Margaret
Whalen, Ph.D., who oversaw the work. Most other studies involved animal
cell lines, she said during a telephone interview. It‚s also the first
time the irreversible effect has been shown, she added.

The findings were presented by one of the contributing researchers,
Sharnise Wilson, a chemistry major and one of Whalen‚s undergraduate
students.

"The results indicate that brief exposures to TPT can cause persistent
suppression of human immune system function," Whalen emphasized.

Although Whalen thinks that most of the TPT levels that agricultural
workers are exposed to in the field are probably below what her group
tested in the lab, "It‚s hard to know what real-life levels for
phenyltins are," she noted.

In the near future, Whalen, in collaboration with Bommanna Loganathan,
Ph.D., of Murray State University in Kentucky, hopes to test blood
samples of agricultural workers who have been exposed to TPT to see
whether significant quantities of the compound can be measured in their
blood.

A type of lymphocyte cell found in the immune system, natural killer
cells aggressively "fight a viral infection or destroy a cancer cell
before other immune system cells recognize that they are there," Whalen
pointed out. "They are quite important." A one-hour exposure to TPT
"causes about a 50 percent to 60 percent loss of the tumor killing
function of the natural killer cell," according to Whalen.

Even after the TPT is removed, the natural killer cells are unable to
regain their strength, as evidenced by tests by Whalen‚s group with human
leukemia cells.

"Despite the fact that the compound is no longer there, they are still
unable to kill the leukemia cell," Whalen said.
Whalen believes the findings "could explain to some extent why compounds
like this seem to increase cancer risks."

The researchers are currently investigating whether interleukin-2 ˜- a
protein produced by other immune system cells ˜- might help reverse the
inhibitory effect of TPT. "It looks like it can to some extent,"
according to Whalen, but she quickly points out that the study is still
ongoing and there is no conclusive data.

The research is primarily funded by the National Institutes of Health‚s
Minority Biomedical Research Support (MBRS) program.

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