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In antibodies, bigger isn't always better.

In Antibodies, Bigger Isn't Always Better

Like a stretch limo trying to get into a mini-car parking space, an antibody too large to get where it's needed may handicap dairy cattle in their fight against infection.

ARS scientists studying the migration of white blood cells into the udders of dairy cows showed that IgM, an important antibody circulating in the blood, did not successfully migrate with the white blood cells to the udder when infections or inflammation occurred.

"On the other hand, [IgG.sub.2], another antibody, or immunoglobulin, stayed attached to the white blood cell, or neutrophil, and made it through the membranes surrounding the udder in fine style," says Max J. Paape of USDA's Agricultural Research Service.

Furthermore, he says, "we found that during their journey through the membranes, neutrophils developed more antibody binding sites. This may increase their ability to bind specific antibodies and attack bacterial invaders."

Paape, who works at the ARS Milk Secretion and Mastitis Laboratory, Beltsville, Maryland, says ways to increase the binding of immunoglobulins to neutrophils in milk may improve protection against udder infection.

Such infections cost dairy farmers $2 billion annually in medication and lost milk production.

In laboratory tests, University of Maryland graduate students Leanne Berning and Millie Worku, who worked with Paape, used a chamber partitioned by a filter with pores about half the size of the neutrophils.

On one side they placed a suspension of neutrophils that had [IgG.sub.2] and IgM immunoglobulins attached to their surfaces. On the other side was a special mixture of fetal calf serum that acted as an attractant to the neutrophils.

After 3 hours the neutrophils that migrated through the membrane were examined in a special cell sorter. The neutrophils lost most of the IgM, but the [IgG.sub.2] immunoglobulin numbers were about the same. Further, new binding sites for IgM and [IgG.sub.2] appeared on the cell surface.

"To see if the results could be repeated in dairy cows, we placed an irritant in their udders to simulate an infection. Neutrophils tested at the site of the bogus infection had also lost their IgM immunoglobulin and had increased numbers of binding sites," says Paape.

Paape speculates that, "because the IgM is so much larger than the other molecules, it is rubbed off in the rather small pores of the membranes as the neutrophils squeeze through."

Antibodies circulate in the blood and are formed when the body's immune system recognizes a "stranger." They are instrumental to the destruction of invading bacteria.

Paape says that "antibodies ride piggy back on neutrophils. They act like antennae to locate the offending bacteria, which the neutrophils then stick to. Ultimately, the neutrophil ingests the bacteria through a process called phagocytosis."

PHOTO : Research assistant Millie Worku operates a flow cytometer, a laboratory instrument that reveals how immunoglobulins bind to neutrophils.
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Title Annotation:migration of antibodies, that are attached to white blood cells, into the udders of dairy cows
Author:Mazzola, Vince
Publication:Agricultural Research
Date:Oct 1, 1991
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