Contents
Coupled Antibodies Fend Off
Mastitis
As most mastitis infections caused by
Staphylococcus aureus occur during milking,
animal caretakers George Kinner (left)
and Stuart Greene take care to ensure that dairy cows' udders are cleaned
properly.
(K8082-1)
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Inside a dairy cow's mammary gland, immune cells that seek out and destroy
invading bacteria have a tough time finding their targets. Staphylococcus
aureus and other mastitis pathogens have a capsule that makes recognition
by immune cells difficult. As a result, a dairy producer with 100 cows can
expect 50 to 80 obvious cases of mastitis in the herd each year.
Despite antibiotics, mastitis costs the U.S. dairy industry more than $2
billion annually, says dairy scientist Max J. Paape, who is with the
Agricultural Research Service
Antibiotics are part of this cost, and they can cause other headaches, Paape
says. The drugs are often ineffective because of resistant pathogens or, in
older cows, repeated treatments. Producers have to wait a few days to sell milk
from antibiotic-treated cows. Cows that don't respond are often sold for
meat--increasing the chance of antibiotic-contaminated beef.
So Paape and his assistants are collaborating with scientists at the
National Institute for Agronomic Research in Nouilly, France, and at the
National Cancer Institute (NCI) in Bethesda, Maryland, to develop a treatment
they hope will help cows fight infection naturally.
Coupled, or bifunctional, antibodies are proving effective against human
cancers in clinical trials of patients who don't respond to traditional
therapy, says Paape. He is with the Immunology and Disease Resistance
Laboratory in Beltsville, Maryland. "This is the first such antibody
developed for domestic animals," he says.
The theory, Paape explains, is that when this coupled antibody is injected
into the mammary gland, one end hooks up to a pathogen--say, S. aureus.
The other end snags its "terminator"--a specialized white blood cell,
called a neutrophil, from the cow's immune system. This contact triggers the
neutrophil to release a lethal spray of hydrogen peroxide. With the bacterium
literally handcuffed to the neutrophil, the hydrogen peroxide bath can't miss:
mastitis meltdown!
Yan Wang, a doctoral candidate working in Paape's lab, made monoclonal
antibodies that bind to a few of these trigger proteins on the surface of
bovine neutrophils. Paape enlisted French researchers Pascal Rainard and
Bernard Poutrel to construct a monoclonal antibody that zeros in on a specific
molecule on the capsule of S. aureus. Then Paape worked with NCI's David
Segal to chemically stitch together the two monoclonals.
A new research associate in Paape's lab, Grant Tomita, will devote 2 years
to studying this and other bifunctional antibodies in vitro-- that is, in
culture in a laboratory--and in the cow herself. If they significantly increase
the killing power of the cow's immune cells, the system will have to be tweaked
for the most effective on-farm application, says Paape. But he already
envisions more bifunctionals to treat many other infectious agents in a variety
of farm animals.--By Judy
McBride, Agricultural Research Service Information Staff.
Max J. Paape and Yan Wang are
at the USDA-ARS
Immunology and Disease Resistance Laboratory, Bldg. 173, 10300 Baltimore
Ave., Beltsville, MD 20705-2350; phone (301) 504-8302, fax (301) 504-9498.
"Coupled Antibodies Fend Off Mastitis" was published in the
June 1998 issue of Agricultural Research magazine. Click
here to see this issue's table of
contents.
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