How Does Psoriatic Disease Affect the Immune System?

Psoriatic disease is an immune-mediated disease that includes psoriasis, along with other comorbidities such as psoriatic arthritis (PsA) and related systemic inflammation. In people living with psoriasis and/or PsA, the immune system is triggered and activated, acting as though there are harmful pathogens attacking the body.

This inflammation can present with noticeable signs such as discoloration of the skin or swelling around joints. However, the overactive immune system may also lead to inflammation a person cannot see. Inside the body, inflammation can affect organs and organ systems and lead to other health conditions (also called comorbidities) associated with psoriatic disease. Comorbidities of psoriatic disease include cardiovascular disease, metabolic syndrome, obesity, hypertension (high blood pressure), type 2 diabetes, anxiety and depression, and more. 

Researchers who study psoriatic disease are still working to identify the substances that trigger this immune response. One possibility could be certain kinds of bacteria acting as antigens (a foreign substance that triggers an immune response). For example, sometimes streptococcal infection (known as strep throat) can trigger a case of guttate psoriasis. Another possible antigen could be antimicrobial peptides, molecules made by the body that are part of the immune system and work as antibiotics.

Normally, it takes 21 to 28 days for cells on the surface of the skin to grow and shed; it may take as few as four days in skin affected by psoriasis, due to the increased immune response. For psoriasis, a flare may include new psoriasis plaques or the return of plaques to a prior location, itch, irritation, or burning.

With PsA, a flare may include new or increased pain, tenderness, swelling, or stiffness in the joints. Flares may last for varying lengths of time and may vary in level of severity.

Having skin affected by psoriasis or joints affected by PsA can be a sign of inflammation occurring in other parts of the body. Even people living with mild psoriasis may have inflammation throughout the body. 

Genes and the Immune System

Genes may hold the key to understanding how the immune system becomes activated in people who have psoriasis and/or PsA, with many loci (specific gene locations) associated with psoriasis. These genes may be involved with the immune system as well as skin barrier functions. [2]

Genetics are important because if one parent has psoriasis, a child has about a 28% chance of developing psoriasis. If both parents have psoriasis, a child has approximately a 65% chance of developing psoriasis. [3] While there may be a genetic predisposition for some, it is possible for people with no family history of psoriatic disease to develop it.

When a specific gene is found to be linked to psoriatic disease, researchers work to determine what the gene does under "normal" conditions. Next, the research tries to determine how the gene behaves differently in a person living with psoriasis or PsA. although this may be a difficult process, having a better understanding of the genetics of psoriatic disease can lead to advancements that can change lives.

Last updated on 11/1/2023 by the National Psoriasis Foundation.