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About one out of every four people who have psoriasis will eventually develop painful swelling in their joints. This condition is known as psoriatic arthritis. If doctors do not treat it effectively, it can cause permanent damage to bones and joints. For many years, the medical community did not fully understand why this complication happens to some people but not others. Now, a group of researchers has found the specific immune cells responsible. They have also tracked the journey of these cells from the skin to the joints. This discovery opens new ways to detect the problem early and stop it before it causes permanent harm.
Scientists from Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU) have found the main mechanism behind this change. Their research was published in the journal Nature Immunology. The study reveals that inflammation in psoriatic skin creates special immune precursor cells. These cells do not stay in the skin. Instead, they travel through the bloodstream to reach joints in other parts of the body.
"These cells can move from the skin to the bloodstream and then travel from there to the joints," explains Dr. Simon Rauber, who led the research group at the university's Department of Medicine 3 for Rheumatology and Immunology. However, Dr. Rauber notes that just moving the cells is not enough to cause disease. He states, "It is interesting that the mere migration of immune cells into the joint is not sufficient to trigger inflammation there."
The critical factor that decides if arthritis develops is the environment inside the joint itself. When the migratory immune cells arrive, they interact with local connective tissue cells known as fibroblasts. In a healthy joint, fibroblasts help keep things balanced and stop inflammation. The study found that in people who develop psoriatic arthritis, this protective function is greatly reduced.