Possible key role of immune system in Schmorl's nodes

Schmorl's nodes (SNs) are common abnormalities in the human spine, which represent herniation of the nucleus pulposus of the intervertebral disc into the adjacent cartilaginous endplate of the vertebra. However, the principle mechanism of SNs is still not fully understood. And the relationship of SNs in the spine and their clinical significance as a source of low back pain in the general population remains unknown. It is therefore important to get better understanding of this. Here, we review the clinical and experiment evidence on inducing of the SNs and correlative back pain, and propose a possible mechanism. Studies showed that once the nucleus pulposus enters into vascular tissue, the immune system could recognize it as a foreign body, and induces the immunological reaction. Then, there would be osteoimmunology action, a crosstalk between the immune system and bone, leading to bone loss by dysregulating T-lymphocyte function, and resulting to the bone absorption. Furthermore, the cytokines are involved in the development of immunological reactions and could be responsible for the significant pathology of symptomatic SNs. Given the above background, we hypothesize that immune system could be a key role in SNs and result in the pain.