According to research out of Boston University, people who are obese have a harder time fighting off infections and may suffer from a weakened immune system as a result. Obesity has long been linked to inflammation and to the development of metabolic diseases triggered by inflammation but, until know, the relationship between obesity and the immune system has been less clear.
The Experiments
This was an experiment in mice that were infected with a type of bacteria that caused gum infections, called Porphyromonas gingivalis. It was discovered that those mice who were obese had a decreased ability to fight off gum infections caused by this type of bacteria when compared to mice who were of normal weight.
According to researchers, scientists have been wondering for years why people who were obese had a hard time clearing up an infection. Now they understand that some immune system mechanisms are dysfunctional because of the obesity and that these immune system dysfunctions explain why obese people have difficulty in wound healing and in healing an infection.
The researchers tied silk threads that were infected with the pathogenic bacteria around the molar teeth of normal weight mice and obese mice. They then compared the responses of the animals to infection by measuring the growth of activity around the teeth and by measuring the amount of bone lost to infection.
Obese mice seemed to have a compromised immune function and were more susceptible to getting the infection and having a more severe case of the infection. The researchers also looked at the amount of the animals’ white blood cells, which provide the best defense against various forms of infection. It was discovered that the white blood cells of mice who were obese had lower levels of a signaling molecule used in infection fighting and that certain genes related to fighting inflammation were defective.
No one knows exactly why obesity has this effect on the immune system but some researchers believe it involves an immune signaling pathway, which controls an immune protein called NF-kB. Changes in this protein may be related to excessive exposure to food so that the body cannot respond the way it should to exposure to pathogens and infection.
Applications to Humans
Researchers believe that the same thing going on in mice applies to humans. People who are obese are known to have a greater incidence of gum disease, when compared to those people who are not obese. Gum disease is caused by bacteria, which results in gum inflammation and loss of bone that supports the teeth underneath.
The researchers believe that obese individuals need to be treated in a different way than non-obese people in order to help them fight off infection. They need to be treated by using more targeted antibiotics to help destroy the offending bacteria. The immune system also needs to be increased in obese people so they can help in fighting off infections.
Another Study
Another study, recently published in PubMed, indicated that obesity accounts for metabolic disease and related conditions, which are caused by obesity. The inflammatory state of obese people shows an increased level of pro-inflammatory cytokines. They believed that the chronic inflammatory state is related to a link between the immune system and fatty tissue.
They called obesity a state of malnutrition, which is believed to alter the immune response by lowering white blood cell counts and negatively affecting cell mediated immune responses. Obesity, it seems, is also caused by an impairment in the immune system.
There has been found to have an increase in leptin in obese people, which is a pro-inflammatory protein. Obesity is also related to a reduction in adiponectin, which is a molecule that activates the immune system. In addition, an excess of nutrients in the body and expansion of fatty tissue seem to trigger stress in the endoplasmic reticulum of cells of all types. Hypoxia (a lack of oxygen) in fatty tissue seems to stimulate the expression of genes that cause inflammation and causes activation of immune cells.
It appears that the presence of obesity around the trunk rather than the total body fat content has a greater impact on the process of inflammation and reduction in the immune cell function. There appears to be some kind of positive feedback loop between adipose tissue inflammation and the altered immune responses seen in obesity, leading to immune-related metabolic diseases.
