How your skin defends itself against acne bacteria

As promised, here is a follow-up post to the acne viewpoint paper that was published in Experimental Dermatology (Ref 1) . This paper was published very recently and summarizes the state-of-the-art of our knowledge about acne. This post explains recent insights in the way sebocytes recognize and respond to bacteria.

Sebocytes are more than skin deep

Scientists used to think that sebocytes (the cells inside the sebacious glands, see the diagram on the right and the Skinny on Acne post), were only involved in producing sebum (oil) for lubrication. However, it is now becoming clear that these cells are much more sophisticated than that.

Neuropeptide Receptors

The cells have now been shown to express several important receptors for neuropeptides on their cell surface. Binding of neuropeptides to these receptors cause the cells to respond by producing cytokines such as IL-6 and IL-8 (Interleukin-6 and Interleukin-8). These are signaling molecules that are involved in inflammation and help to stimulate immune responses. For an introduction to cytokines, see this Wikipedia post

TOLL Receptors

Sebocytes now also have been shown to express TLR2 and TLR4. These are so-called TOLL-like receptors and are components of the innate immune system. Your innate immune system does not make antibodies and does not require exposure to pathogens to learn which antibodies to make. Instead, it relies on pre-existing receptors (the TOLL-like receptors) that recognize certain classes of micro-organisms. As a result, this part of your immune system can respond very quickly to an infection, and does not first have to make antibodies. The innate immune system is your first line of defense, so to speak. TLR2 and TLR4 recognize certain bacteria directly, as well as indirectly due to the endotoxin and other molecules that these bacteria produce.

Bactericidal agents

Researchers now also have found that that sebocytes secrete bactericidal substances such as defensins (small proteins that are active against bacteria, fungi and viruses), as well as oleic acid and palmitic acid. The latter two are fatty acids that are known to kill Gram-positive bacteria. The major culprit associated with acne, Propionibacterium acnes, is Gram-positive.

Conclusion

So, you can see that the skin is well equipped to defend itself against all sorts of bacteria, including acne bacteria. Unfortunately, in the process of eliminating the infection, a temporary inflammation is created that manifests itself as acne.

The good news is that new scientific insights in how skin functions, such as the ones discussed above, eventually will lead to new treatments. It will take time, but more effective acne treatments may be on the horizon.