We will present a mechanistic model of the role of the immune system in the persistence of chronic pain, especially nociceptive pain.  This model is designed to support the development and assessment of therapeutic agents.  In contrast to other quantitative modeling approaches (statistical or descriptive models), a mechanistic model encodes a molecular hypothesis, and makes testable predictions arising from that hypothesis, even when the underlying system is complicated by phenomena such as negative feedback.  The mechanistic model reported here is designed to produce testable predictions within the context of analgesic clinical trials.