The Microbiome--Another Psoriasis Trigger in Hiding?

Triggers of plaque psoriasis have long been known to include factors like stress, the environment, illness, or diet.  Some of these triggers can be controlled, others cannot, making managing plaque psoriasis a struggle at times.  A possible new trigger—microbiota-- may complicate this relationship even further, and may be lurking in your body as you’re reading this!  Microbiota on the skin or in the gut of the body has recently been proposed as a possible contributor to psoriasis flare-ups.  So how does this work, and why would bacteria that naturally live within our body space suddenly cause a commotion?

The immune system connection

Our bodies are composed of so many things that work harmoniously together to keep us in tip-top shape.  One example of this teamwork comes from microbiota. Microbiota is composed of bacteria, fungi, and other single-cell organisms that live in our bodies.  Microbiota live in our intestines or on our skin and have various functions. These functions include helping us digest food, breaking down things into usable enzymes and vitamins, or warding off potential incoming infections. The whole of this microbiota, and how they work in tandem with our bodies, is called the microbiome.

Our immune system and its functions are divided into two main responses: innate immunity and adaptive immunity. Innate immune responses are mobilized immediately and work against things that are seen as “foreign” to our bodies, regardless of what they are. Adaptive immune responses are mobilized more slowly and are targeted response to each specific “foreign” invader.

Psoriasis is an autoimmune disease where specific parts of the immune system have been implicated in producing the classic inflammatory response that results in skin lesions in addition to other symptoms. Most psoriasis autoimmune research to date has focused on psoriasis and the adaptive immune response, and specific proteins have been identified: TNF alpha, IL-17-A, and IL-12/23. This research has led to the development of biologic treatments that target these proteins/inflammatory pathways.

Some studies have shown that psoriasis inflammation and resulting skin lesions are an innate immune response1.  In fact, many of the genes involved in the psoriasis inflammation pathways are actually ones directly related to the innate immune system.  The innate immune system develops before we are even born, and fights off invaders in a non-specific manner.  In other words, if an infection is bad enough to trigger the innate immune system as we get older, our body will fight everything and anything, in an attempt to get rid of the original threat.  However, this means that sometimes “good” cells can be attacked, and can lead to inappropriate responses of the body, such as making way too many keratinocytes, or initiating an inflammatory sequence, both leading to plaque psoriasis lesions.

Regardless of whether we are looking at innate or adaptive immune responses, our immune system usually recognizes the “good” bacteria in our microbiome, and our body generally leaves them alone. However, with autoimmune conditions like psoriasis and Crohn’s disease, the role of the microbiome becomes less clear cut, and our body may get confused and attack bacteria it shouldn’t.

Microbiome and dysregulation of immune system

The field of microbiome research is relatively new and there are only a few studies to date that look at the link between the microbiome and psoriasis. One study advances a theory that the innate immune system may also have an important role in understanding differential responses that happen in people with psoriasis, based upon differences in their microbiome1. This type of response, for example, might be seen in a psoriasis flare-up, or a rebound response that happens after a treatment is halted.

Some studies have suggested that microbiota that live on the skin are responsible for triggering the pro-inflammatory response that is associated with psoriasis skin symptoms2.  Analysis of specific skin microbiota, and their ability to trigger a similar immune response to the one observed in psoriasis, could indicate that the skin microbiota is where the problem lies.

Other researchers have proposed a model where the gut microbiome plays a more prominent role in psoriasis, similar to what is seen in Crohn’s disease2. In Crohn’s, the immune tolerance to natural gut microbiota is broken down, causing the body to attack the bacteria it needs, and causing many complications.  Because of the known co-occurrence of Crohn’s disease in people with psoriasis, gut microbiome may be a source of microbial triggers for psoriasis, in addition to microbiome of the skin. Regardless of whether research is focusing on skin or gut microbiota, it seems that disturbances in microbiota can result in the immune system dysregulation that underlies psoriasis and other autoimmune conditions3.

So why does this matter?

Since this research is in its infancy, it is challenging to see all the potential implications. However, food allergies and sensitivities may be one area where this research can shed some light.  For example, rather than foods triggering psoriasis directly, specific foods may trigger a reaction from our microbiome that is pro-inflammatory for psoriasis.

This is not to say that the skin or gut microbiome is the cause of psoriasis, but that the specific role(s) of the microbiome is not clear, and may be one of several contributing causes for the overall immune dysregulation that is part of psoriasis3. Things that destabilize the long-term stasis our body has with its microbiome, may trigger inflammation or a flare-up.

While the scientific debate about the role of the microbiome in autoimmune disease, and psoriasis specifically may be somewhat confusing, it is an important piece of the puzzle. There is still a lot more research to be done before there are clear answers that will help with psoriasis treatment. If the relationship between psoriasis and the microbiome bears out in future research, it will certainly add a layer of complexity to determining effective treatment options. In the meantime, many of these results suggest that natural bacteria in the body, whether it comes from the skin, the gut, or both, may be a psoriasis trigger that has the potential to be better controlled in the future.

Editorial note: Some additional interesting facts about the human microbiome4:

  • As you age, your gut microbiome becomes more diverse.
  • A more diverse gut microbiome environment is considered more healthy.
  • The use of antibiotics can substantially alter the gut microbiome, reducing its diversity.
  • The more different types of plants a person eats the greater their gut microbiome diversity.
  • Moderate alcohol consumption can also increase gut microbiome diversity.

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