Obesity Weakens Immune Response

Obesity Weakens Immune Response
WEDNESDAY, Dec. 12 (HealthDay News) -- Obese people find it harder tofight infections, and a weakened immune response may be to blame, suggestsa new study from Boston University researchers.
In experiments with mice infected with the bacteria Porphyromonasgingivalis, obese mice had less ability to battle gum infection thantheir normal-weight counterparts, according to the report in this week'searly online edition of the Proceedings of the National Academy ofSciences.
"For years, we have had difficulty understanding why obese people havedifficulty clearing an infection," said lead researcher Dr. Salomon Amar,associate dean for research at the university's School of DentalMedicine.
"Now we understand that dysfunction in some of the mechanisms, as aresult of the obesity, explain difficulty in clearing the infection andalso the difficulty in wound healing," Amar said.
In the study, Amar's team tied silk threads infected with the bacteriaaround the molars of obese and normal-weight mice. They then compared theanimals' responses to infection, by measuring both the amount of bone lossand the growth of the bacteria around their teeth.
The researchers found that the obese mice had a compromised immuneresponse to the bacteria, which made the animals more susceptible to theinfection.
Amar's group also looked at the animals' white blood cells, which arethe main line of defense against infection. The white cells of obese micehad lower levels of an important signaling molecule, and some of the genesthat fight inflammation were altered, the researchers found.
Why obesity has this effect isn't clear, but the researchers think itmay involve a signaling pathway that controls a protein called NF-kB.Alterations in this protein may be caused by constant exposure to food,Amar explained. "At some point, the body doesn't respond properly toinfection," he said.
The same mechanism is at work in humans, Amar added. In fact, studiesin obese people have shown they are more likely to have gum disease thannon-obese people. The disease is caused by bacteria, which causesinflammation and destruction of the bone underlying teeth.
Amar thinks that obese people need to be treated differently to helpthem fight infections. "We need to be more aggressive in the use oftargeted antibiotics in infections among obese people," he said. "Also, weneed to boost the immune response."
One expert agreed the finding sheds light on the connection betweenobesity and infection.
"Very interesting paper," said Dr. Sara G. Grossi, a senior researchscientist at the Brody School of Medicine of East Carolina University."This is a study that needed to be done, with very interesting results andimplications for both obesity and periodontal disease -- two diseases thatare easier to prevent than to treat."