Neuroimmune interactions and osteoarthritis pain: focus on macrophages

Abstract

Bidirectional interactions between the immune system and the nervous system are increasingly appreciated as playing a pathogenic role in chronic pain. Unraveling the mechanisms by which inflammatory pain is mediated through communication between nerves and immune cells may lead to exciting new strategies for therapeutic intervention. In this narrative review, we focus on the role of macrophages in the pathogenesis of osteoarthritis (OA) pain. From regulating homeostasis to conducting phagocytosis, and from inducing inflammation to resolving it, macrophages are plastic cells that are highly adaptable to their environment. They rely on communicating with the environment through cytokines, growth factors, neuropeptides, and other signals to respond to inflammation or injury. The contribution of macrophages to OA joint damage has garnered much attention in recent years. Here, we discuss how macrophages may participate in the initiation and maintenance of pain in OA. We aim to summarize what is currently known about macrophages in OA pain and identify important gaps in the field to fuel future investigations.

Keywords: Animal models; Inflammation; Macrophages; Neuroimmunity; Osteoarthritis; Pain.

Figure 1.

In the context of a chronic progressive disease such as osteoarthritis, the interactions between macrophages, tissue resident cells, and nociceptors at the level of the joint, DRG, and spinal cord may provide an ever-changing network of signals that are important in perpetuating pain. These signaling molecules include chemokines, cytokines, neurotrophins, and proresolving mediators, among others.