Researchers found that adipocytes, or fat cells, under the skin protect us against infection by producing antimicrobial peptides that stave off pathogens
Dr. Richard Gallo, professor and chief of dermatology at the UC-San Diego School of Medicine, and colleagues say they have demonstrated that adipocytes produce antimicrobial peptides that stave off pathogens.
The researchers publish their findings in the journal Science.
The researchers explain that they chose to study this bacterium in particular as past studies had identified its presence in the fat layer of the skin. As such, they wanted to see whether this fat aided the prevention of skin infections.
Adipocytes produced high levels of an antimicrobial peptide in response to S. aureus
Within a few hours of exposing the mice to S. aureus, the researchers witnessed a significant rise in the number and size of adipocytes at the infection site.
The most surprising finding, however, was that the adipocytes produced large amounts of cathelicidin antimicrobial peptide (CAMP) - an antimicrobial peptide (AMP) that forms a part of the innate immune system response to kill bacteria, viruses and other potentially harmful microbes.
"AMPs are our natural first-line defense against infection," explains Dr. Gallo. "They are evolutionarily ancient and used by all living organisms to protect themselves."
Commenting on their findings, Dr. Gallo says:
"It was thought that once the skin barrier was broken, it was entirely the responsibility of circulating [white] blood cells - like neutrophils and macrophages - to protect us from getting sepsis.
But it takes time to recruit these cells [to the wound site]. We now show that the fat stem cells are responsible for protecting us. That was totally unexpected. It was not known that adipocytes could produce antimicrobials, let alone that they make almost as much as a neutrophil."
Next, the researchers exposed mice that were either unable to produce adipocytes or unable to express satisfactory amounts of AMPs - particularly CAMP - to S. aureus.
The team found that both groups of mice developed more severe and frequent infections, which confirmed their previous findings that adipocytes play a role in warding off pathogens.
Obese individuals have higher CAMP levels
However, Dr. Gallo describes the presence of AMPs - especially CAMP - as a "double-edged sword," noting that people with low levels of CAMP often experience infections.
"The best example is atopic eczema," Dr. Gallo notes. "These patients can experience frequent Staph and viral infections." People with too much CAMP, however, may be at increased risk of autoimmune and inflammatory diseases, such as lupus and psoriasis.
On analyzing human adipocytes, Dr. Gallo and colleagues found they also produce CAMP. What is more, obese individuals - who have higher levels of adipocytes - were found to have higher levels of CAMP in their blood than people of a normal weight.
"Defective AMP production by mature adipocytes can occur due to obesity or insulin resistance, resulting in greater susceptibility to infection, but too much cathelicidin may provoke an unhealthy inflammatory response," says Dr. Gallo, adding:
"The key is that we now know this part of the immune response puzzle. It opens fantastic new options for study.
For example, current drugs designed for use in diabetics might be beneficial to other people who need to boost this aspect of immunity. Conversely, these findings may help researchers understand disease associations with obesity and develop new strategies to optimize care."
Medical News Today recently reported on a study published in the journal Psychological Science suggesting hugging could protect us against infection.