The report by a team of researchers at Indiana University, Ohio State University and Johns Hopkins University was made available online this week by The Royal Society. Their study is the first to show that even a moderate loss of fat leads to decreased amounts of infection-fighting IgG antibodies.

"We were able to show that even a subtle decrease in fat can decrease humoral immunity, which has the potential to increase disease susceptibility," said Indiana University biologist Gregory Demas, who led the study. "We knew that immune function is energetically costly, but it is now clear that animals use energy stored as fat to bolster immunity and likely to combat infection."

The researchers also found that immune system function improved after the regrowth of fat tissue that had been removed.

The research team divided 54 adult male prairie voles and 36 adult male Siberian hamsters into three experimental groups. The individuals from one of these groups had epididymal white adipose tissue removed, the second group had inguinal white adipose tissue removed, and the third group had a surgical procedure but had no adipose tissue removed.

Half of the rodents in each of the three groups were then exposed to an immune system-roiling antigen called keyhole limpet hemocyanin (KLH) four weeks after surgery. The other half of each group received KLH 12 weeks after surgery. KLH is known to induce a strong immune response in voles and hamsters without making the animals sick.

After a few days, the researchers measured each rodent's bloodstream concentrations of IgG antibodies raised in response to the presence of KLH. Lower concentrations of the antibodies signify impaired immune function. The researchers found that im
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Contact: David Bricker
brickerd@indiana.edu
812-856-9035
Indiana University
28-Mar-2003