The constantly changing environment challenges us humans with ever mutating pathogens. A sturdy physical barrier is crucial in maintaining a strong front to evade constant attacks. This physical barrier in humans is the skin and serves as the first line of defense.
In instances, when the pathogens, such as bacteria and the viruses, do gain entrance into the body, a second line of defense is present to stave off the attack and contain the infection. The agents involved in doing so are, obviously, the white blood cells present in the body. These happen to, not only circulate in the blood, but are also present in various tissues.
The researchers at the UC-San Diego School of Medicine, led by Dr. Richard Gallo, who is the chief of the dermatology department, were intrigued to see that the first line defense delved a bit deeper than the superficial skin layers. And they wanted to study how the bacteria were dealt with when they entered the body.
Normally in humans, when an infection does occur, the bacterium, especially Staphylococcus aureus, which is normally present on the skin, seems to get trapped within the adipose cells layer. The researchers decide to replicate the response in mice by infecting them, to illicit the responses normally seen in humans. Staph aureus is normally present in the skin and causes cellulitis and impetigo in humans.
The results of the experiment show that long before the white cells, within the tissues, showed reaction to the invasion, the adipose tissues in the body began to proliferate and produce a special compound called cathelicidin antimicrobial peptide or CAMP. The response that the adipose cells show is actually part of the innate immunity and CAMP is an antibacterial substance which eliminates harmful pathogens.
the researchers say, “It was thought that once the skin barrier was broken, it was entirely the responsibility of circulating blood cells – like neutrophils and macrophages – to protect us from getting sepsis. But it takes time to recruit these cells. 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 antimicrobial, let alone that they make almost as much as a neutrophil.”
According to the researcher, AMPs or antimicrobial peptides are essentially the first line defense mechanism employed by all organisms, since ancient times. What is of particular surprise is the ability of the fat cells to make use of this particular mechanism to ward off infections.
“AMPs are our natural first-line defense against infection. They are evolutionary ancient and used by all living organisms to protect themselves,” say the researchers.
However, the researchers note that levels of AMPs vary with the amount of fat tissue a person has. People who have insufficient levels of adipose tissue have low levels of AMPs and are more susceptible to infection.
“The best example is atopic eczema. These patients can experience frequent Staph and viral infections,” explained Dr. Gallo.
Whereas, obese people have a high fat cell content, and hence are liable to produce more AMPs which can have a detrimental effect on health through autoimmune reactions of the body.
“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,” say the researchers.