The immune system can be divided into the innate and adaptive arms. Historically, most of the research into the pathogenesis of spondylarthritis (SpA) and other types of chronic arthritis focused on the adaptive immune system. Recently, the pendulum has shified, and much current work in SpA focuses on innate immunity. Herein, I summarise evidence demonstrating that both the innate and the adaptive arms of the immune system are involved in the pathogenesis of SpA, propose a mechanism in which both arms interact to maintain chronic arthritis, and discuss potential research directions. © Copyright Clinical and Experimental Rheumatology 2011.