How Does Chronic Inflammation Affect the Joints in Psoriatic Arthritis Patients?
Psoriatic arthritis (PsA) is a form of chronic arthritis that is associated with psoriasis. While the exact pathogenesis (cause) of PsA is unknown, it is believed to share common mechanisms of development with psoriatic skin symptoms. Normal immune responses become abnormally activated in psoriasis following an environmental trigger, such as physical stress, trauma or infection.
In the case of PsA, the disease causes an inflammatory response in the joints. People with psoriasis have an elevated risk for cardiovascular disease, which can lead to heart attacks and strokes. This risk is increased in people with PsA, which experts believe reflects the overall burden of systemic inflammation throughout the body.1
Healthy immune response
In a healthy immune response, the body’s immune system recognizes foreign substances by the antigens on the surface of invader’s cells. The immune system consists of white blood cells and certain chemicals and proteins in the blood, such as antibodies, complement proteins, and interferon. Some of these attach to foreign substances in the body, while others work together to help the immune cells.2
One of the white blood cell types is the T-cell lymphocyte. T lymphocytes, or T-cells, attack the antigens directly and help control the immune response. They also release chemicals called cytokines that govern the entire immune response.2
An inflammatory response is triggered when bacteria, trauma, toxins, or heat injure the tissues in the body. Damaged cells release chemicals that cause blood vessels to dilate, permitting increased blood flow into the tissue, which causes swelling. This process helps isolate the foreign substance from spreading further into the body.2
The abnormal immune response of PsA
Abnormal activation of the immune response contributes to the chronic disease processes in both psoriasis and PsA.1 In psoriasis and PsA, the immune response, and particularly the inflammatory response, activates and begins to attack healthy tissue. This is why PsA and psoriasis are characterized as autoimmune diseases.3
Researchers have found several specific T-cells and cytokines that are abnormally active in PsA, including, but not limited to:1
- Tumor necrosis factor (TNF) – A cytokine released by T lymphocytes that has multiple actions, including the ability to induce necrosis (death) of tumor cells. It also triggers a wide range of inflammatory actions. Drugs that block the action of TNF have been shown to be beneficial in reducing the inflammation of arthritis.1,4
- Th17 cells – T helper 17 cells are a subset of T-cells that are responsible for clearing pathogens during host defense reactions and inducing tissue inflammation in autoimmune disease.1,5
- Interleukin-17A – IL-17A is a cytokine produced by the Th17 cells that exerts a host defense role in infectious disease and promotes inflammation in autoimmune diseases.1,6
- Interleukin 23 – IL-23 is another cytokine produced by the Th17 cells that plays a role in the inflammatory pathology in PsA.1,7
Inflammation in the joints leads to pain
Immune responses – both normal and abnormal as seen in PsA – that cause inflammation are painful because the excess blood flow and the substances secreted by the white blood cells and excess fluid irritate the nerves in the area, sending pain signals to the brain.8