Not All Fat is Bad: Fat Cells Boost Immune System

Not all fat is bad fat. Scientists have found that when it comes to skin infections, a healthy and robust immune response may depend greatly on what lies beneath: fat cells.

"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," said Richard Gallo, the principal author of the new study, in a news release. "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 neutrophil."

When it comes to protecting ourselves against microbial infection, our bodies' response is complex. It involves numerous cell types and eventually culminates in the arrival of neutrophils and monocytes, which are specialized cells that devour targeted pathogens. Before these circulating white blood cells arrive on the scene, though, the body requires a more immediate response, which is where skin cells come in.

In order to see the response to infection, the researchers exposed mice to Sta[ju;pcpccis aureus, which is a common bacterium and a major cause of skin and soft tissue infections in humans. Within hours, the scientists detected a major increase in both the number and size of fat cells at the site of infection. More importantly, the fat cells produced high levels of an antimicrobial peptide (AMP), called cathelicidin antimicrobial peptide, or CAMP. AMPs are molecules used by the immune response to directly kill invasive pathogens.

"The key is that we now know this part of the immune response puzzle," said Gallo. "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."

The findings are published in the journal Science.

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