A new study has revealed why arthritis has a tendency to flare up in the same location instead of around the body.
When joints flare up in people with rheumatoid arthritis and related diseases, the joints involved are often the same as those previously affected. For example, if arthritis started in the right knee, it is much more likely to flare there than in the left knee, even if the arthritis had been in remission for years. Because of this, each patient develops a highly individual disease pattern, though why this is so has remained unclear.
“Overwhelmingly, flares occur in a previously involved joint,” said Peter Nigrovic, MD, chief of the division of immunology at Boston Children’s Hospital. “Something in that joint seems to remember, ‘this is the joint that flared before.’”
A new study, co-led by Dr Nigrovic and published in Cell Reports, shows where that memory is housed: in a type of immune cell called a tissue-resident memory T cell. Specifically, these T cells reside in the synovium, the tissue that lines the inside of the capsule surrounding the joint.
“We showed that these T cells anchor themselves in the joints and stick around indefinitely after the flare is over, waiting for another trigger,” said Dr Nigrovic. “If you delete these cells, arthritis flares stop.”
The team demonstrated this phenomenon in three separate mouse models of inflammatory arthritis. Two models used chemical triggers to cause joint inflammation, and the third had a protein knocked out that blocks the pro-inflammatory cytokine IL-1. Once activated, resident memory T cells in the joints rallied other immune cells, leading to an arthritis flares limited to specific joints. Elimination of these T cells prevented further flares from occurring.
“Right now, treatment of rheumatoid arthritis has to continue lifelong; although we can successfully suppress disease activity in many patients, there is no cure,” said Dr Nigrovic. “We think our findings may open up new therapeutic avenues.”
Dr Nigrovic also believes the findings apply to other types of autoimmune arthritis, including juvenile idiopathic arthritis.
Dermatology provided a cue for the researchers: tissue-resident memory T cells were originally found in skin, where a ‘memory’ pattern is well known to dermatologists. In psoriasis, for example, patients get recurrent plaques in the same places. The same often holds true in cutaneous hypersensitivity reactions, such as reactions to nickel in jewelry or wristwatches. “A person reacting to nickel through a belt buckle may also develop a rash on their wrist, where they wore a nickel-containing watch as a child,” observed Dr Nigrovic.