By Rosalie Marion Bliss
Agricultural Research Service (ARS) scientists are testing a
plant-produced, therapeutic protein, which thwarts bacteria that cause
inflammatory udder disease in dairy cows.
They turned a laboratory-produced plant virus into a delivery vehicle
that carries a specific gene. The target gene expresses large quantities of
a protein called CD14. When the virus reproduces itself inside plant cells,
it generates CD14.

The researchers designed the virus to use the plant as a
patent-pending "biofactory" that rapidly accumulates usable quantities of
the therapeutic CD14 protein. A tagging system?which the researchers built
into the technology?allows high levels of the CD14 protein to be harvested
from mashed leaves. Potentially, fifty plants could provide enough purified
protein to treat a herd of 500 cows.

The CD14 protein is naturally present in cows' milk and blood plasma.
Increased amounts of the protein in body fluids may help improve protection
against bacterial attack. CD14 binds to and neutralizes a toxin which is
present in the outer membrane of the bacterium Escherichia coli that causes
mastitis. This binding enhances the cow's immune response, which contributes
to a rapid clearance of bacteria before infection gains a foothold.

ARS molecular biologist Lev Nemchinov and plant pathologist Rosemarie
Hammond produced the unique plant virus at the agency's Molecular Plant
Pathology Laboratory in Beltsville, Md. After a small drop of the virus'
transmittable RNA has been rubbed onto plant leaves, the CD14 gene begins to
make the protein.

ARS colleagues infused the protein into one of a test cow's four
teats, or quarters. All four quarters were then exposed to E. coli. Fewer
viable bacteria were recovered from the quarter that received the CD14
treatment than from those that did not receive the plant-derived protein.

Mastitis costs dairy farmers billions annually from incapacitated cows
and milk that can't be sold, according to experts.

Read more about this research in the September 2007 issue of
Agricultural Research magazine.

ARS is the U.S. Department of Agriculture's chief scientific research
agency.


[www.ars.usda.gov]