Our bodies are constantly bombarded with microorganisms in the environment such as bacteria and viruses, many of which could potentially cause disease. That’s why we are endowed with numerous physical barriers, such as the skin or sticky mucous membranes, which prevent pathogens from entering the body. If bugs breach these natural defense mechanisms, it is the job of the immune system to get rid of the invader before it can cause harm. But in an unexpected twist, it now turns out that we also have another set of previously unknown helping hands: fat.
According to a new study, fat cells just beneath our skin could actually be the first responders to invaders, buying members of our immune system time to reach the site of entry. Interestingly, lab investigations found that these cells were capable of producing antimicrobial compounds, suggesting they could be playing an important role in fighting off bacteria and other invading pathogens.
Our immune system is a highly complex, diverse and adaptive network of cells and chemicals that work in concert to protect us from pathogens and other foreign substances. If pathogens manage to breach our first line of defense, a cascade of events is triggered which ultimately results in the arrival of specialized white blood cells, such as neutrophils, which literally gobble up the invaders.
However, these immune soldiers take time to arrive on the scene, which is why other cells residing at the site of infection also help fend off microbes. These include epithelial cells, which cover our exterior surface and line our body cavities, and mast cells, which predominantly play roles in allergy. However, researchers suspected that there may be another player, fat cells, although there was no convincing evidence to back this up.
To find out more about the potential role of fat cells, scientists from the University of California, San Diego, infected mice with Staphylococcus aureus, a common bacterium that often causes skin and soft tissue infections in humans. As described in Science, within just a few hours, a significant increase in the number and size of fat cells (adipocytes) was observed at the site of infection. Furthermore, these cells were found to produce a type of antimicrobial substance called cathelicidin antimicrobial peptide, or CAMP. Antimicrobial peptides (AMPs) are small proteins with broad activity against bacteria, viruses and fungi which employ diverse mechanisms to kill target cells.
Taking this one step further, they then investigated what happened when they infected mice either lacking healthy fat cells beneath the skin, or whose adipocytes produced significantly less AMPs, including CAMP. They found that these animals lost the capacity to inhibit bacterial growth and thus suffered more severe infections.
Of course, this doesn’t necessarily represent what is happening in humans; however, they did find that lab grown human adipocytes produce CAMP, suggesting similar mechanisms may be at play. Furthermore, obese humans were found to possess more CAMP in their blood than subjects of normal weight.
These results do not mean that having more fat will make your body better at fighting infections, the researchers caution. In fact, obesity can result in defective AMP production, which would actually increase susceptibility to infection, the researchers said.