When joints flare up in people with rheumatoid arthritis, they are often the same as the joints affected previously, sometimes years prior. Something in that joint seems to remember, "this is the joint that flared before." A new study shows where that memory is housed: immune cells known tissue-resident memory T cells that reside in the synovium, the tissue that lines the inside of the capsule surrounding the joint. The researchers hope to find a practical way to target these cells to treat intractable inflammatory arthritis.