Obesity Linked to Weaker Immunity in Animals

Obese mice are less able to fight off bacterial infection than lean mice, according to a study released this week that supports emerging evidence of a link between obesity and a dysfunctional immune system.

In a study on laboratory mice infected with a bug that causes periodontal disease, obese mice had a blunted immune response to the infection and increased susceptibility to gum disease compared to lean mice.

The obese mice also had much higher rates of bone loss.

When researchers examined the rodents 10 days after they were infected with the bacterium Porphyromonas gingivalis, the heavier mice had a 40 percent increase in alveolar bone loss than the lean mice.

The alveolar bone is the bone or ridge that contains the tooth sockets on the upper and lower jaw.

Previous studies have shown that obese people are more likely to suffer from periodontal disease than their leaner counterparts and this study provided some clues as to why that is.

Blood tests on mice that had been infected with the bacterium P. gingivalis revealed irregularities in the production of cytokines in the obese mice, compared to the “control” or lean mice.

Cytokines are proteins or peptides that signal immune cells such as T-cells and macrophages to travel to the site of infection.

Researchers also analysed the macrophages, the white blood cells that form a major line of antibacterial defense.

They found that levels of key signaling molecules were significantly lower in the macrophages from the obese rodents and the expression profile of inflammation-related genes was altered compared to the control mice.

The researchers said it’s not clear how obesity compromises the immune system, but they suspect a particular signaling pathway involving a transcription factor NF-kB may be involved. NF-kB plays a key role in the immune response to infection.

The study appears in the journal, The Proceedings of the National Academy of Sciences, and was conducted by scientists in the School of Dental Medicine at the University of Boston Medical Center.

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