D2I2.
autoimmune

Reactive arthritis

Reactive , previously known as Reiter's , is a form of arthritis that develops in response to an in another part of the body (cross-reactivity). Coming into contact with and developing an infection can trigger the disease. By the time a person presents with symptoms, the "trigger" infection has often been cured or is in remission in cases, thus making determination of the initial cause difficult.

Underlined words are explained — tap any of them.

Plain-language summary adapted from Wikipedia. Not medical advice.