In a new study, researchers found that antibodies existing in the joints before the onset of rheumatoid arthritis can cause pain.
They believe the finding could help develop new ways of reducing pain caused by rheumatoid arthritis and other autoimmune diseases.
The research was done by a team from Karolinska Institutet in Sweden report.
Rheumatoid arthritis is an autoimmune disease that happens when immune cells attack the cartilage and bone of the joints.
A common early symptom is joint pain, but even before that, the body has started to produce immune antibodies against proteins in the joint.
In that case, pain can appear before any sign of inflammation in the joints and can remain a problem after it has healed.
In the new study, the team aimed to find out how these autoantibodies can generate pain.
They found that the antibodies that had been designed not to activate immune cells and trigger inflammation could also induce pain-like behavior in mice.
The mice became more sensitive to pain even before there were any signs of inflammation in the joints.
The team found that the antibodies that caused the behavioral change form so-called immune complexes, which comprised clusters of antibodies and cartilage proteins in the joints. These complexes activate pain cells.
The researchers explain that antibodies in these immune complexes can activate the pain neurons directly.
The antibodies also can affect the pain neurons in conditions without any distinct tissue damage or inflammation.
The team believes that human pain neurons also have antibody receptors that are functionally similar to those they found on the mouse pain neurons.
This means their new findings are also relevant to humans.
The results can explain the early pain symptoms in rheumatoid arthritis patients. In addition, joint and muscle pain are also common symptoms of other autoimmune diseases.
The researchers believe that the new finding can explain non-inflammatory pain caused by other autoimmune diseases too.
They hope to lay the groundwork for a new way of reducing pain caused by rheumatoid arthritis and other autoimmune diseases
The lead author of the study is Camilla Svensson, professor at the Department of Physiology and Pharmacology, Karolinska Institutet.
The study is published in the Journal of Experimental Medicine.
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