The Immune Privilege of the Intervertebral Disc: Implications for Intervertebral Disc Degeneration Treatment

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Abstract

The intervertebral disc (IVD) is the largest avascular organ of the body. It is composed of three parts: the nucleus pulposus (NP), the annulus fibrosus (AF) and the cartilaginous endplate (CEP). The central NP is surrounded by the AF and sandwiched by the two CEPs ever since its formation. This unique structure isolates the NP from the immune system of the host. Additionally, molecular factors expressed in IVD have been shown inhibitive effect on immune cells and cytokines infiltration. Therefore, the IVD has been identified as an immune privilege organ. The steady state of immune privilege is fundamental to the homeostasis of the IVD. The AF and the CEP, along with the immunosuppressive molecular factors are defined as the blood-NP barrier (BNB), which establishes a strong barrier to isolate the NP from the host immune system. When the BNB is damaged, the auto-immune response of the NP occurs with various downstream cascade reactions. This effect plays an important role in the whole process of IVD degeneration and related complications, such as herniation, sciatica and spontaneous herniated NP regression. Taken together, an enhanced understanding of the immune privilege of the IVD could provide new targets for the treatment of symptomatic IVD disease. However, the underlying mechanism above is still not fully clarified. Accordingly, the current study will extensively review and discuss studies regarding the immune privilege of the IVD.

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Most cited references 80

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Role of cytokines in intervertebral disc degeneration: pain and disc content.

Makarand Risbud, Irving Shapiro (2014)

Degeneration of the intervertebral discs (IVDs) is a major contributor to back, neck and radicular pain. IVD degeneration is characterized by increases in levels of the proinflammatory cytokines TNF, IL-1α, IL-1β, IL-6 and IL-17 secreted by the IVD cells; these cytokines promote extracellular matrix degradation, chemokine production and changes in IVD cell phenotype. The resulting imbalance in catabolic and anabolic responses leads to the degeneration of IVD tissues, as well as disc herniation and radicular pain. The release of chemokines from degenerating discs promotes the infiltration and activation of immune cells, further amplifying the inflammatory cascade. Leukocyte migration into the IVD is accompanied by the appearance of microvasculature tissue and nerve fibres. Furthermore, neurogenic factors, generated by both disc and immune cells, induce expression of pain-associated cation channels in the dorsal root ganglion. Depolarization of these ion channels is likely to promote discogenic and radicular pain, and reinforce the cytokine-mediated degenerative cascade. Taken together, an enhanced understanding of the contribution of cytokines and immune cells to these catabolic, angiogenic and nociceptive processes could provide new targets for the treatment of symptomatic disc disease. In this Review, the role of key inflammatory cytokines during each of the individual phases of degenerative disc disease, as well as the outcomes of major clinical studies aimed at blocking cytokine function, are discussed.

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Disc in flames: Roles of TNF-α and IL-1β in intervertebral disc degeneration.

Z Johnson, Z Schoepflin, H-H Choi … (2015)

The intervertebral disc is an important mechanical structure that allows range of motion of the spinal column. Degeneration of the intervertebral disc--incited by aging, traumatic insult, genetic predisposition, or other factors--is often defined by functional and structural changes in the tissue, including excessive breakdown of the extracellular matrix, increased disc cell senescence and death, as well as compromised biomechanical function of the tissue. Intervertebral disc degeneration is strongly correlated with low back pain, which is a highly prevalent and costly condition, significantly contributing to loss in productivity and health care costs. Disc degeneration is a chronic, progressive condition, and current therapies are limited and often focused on symptomatic pain relief rather than curtailing the progression of the disease. Inflammatory processes exacerbated by cytokines tumour necrosis factor-α (TNF-α) and interleukin-1β (IL-1β) are believed to be key mediators of disc degeneration and low back pain. In this review, we describe the contributions of TNF-α and IL-1β to changes seen during disc degeneration at both cellular and tissue level, as well as new evidence suggesting a link between infection of the spine and low back pain, and the emerging therapeutic modalities aimed at combating these processes.

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Classification of age-related changes in lumbar intervertebral discs: 2002 Volvo Award in basic science.

Helmut Rohrbach, Sabine Weissbach, Norbert Boos … (2002)

A histologic study on age-related changes of the human lumbar intervertebral disc was conducted. To investigate comprehensively age-related temporospatial histologic changes in human lumbar intervertebral disc, and to develop a practicable and reliable classification system for age-related histologic disc alteration. No comprehensive microscopic analysis of age-related disc changes is available. There is no conceptual morphologic framework for classifying age-related disc changes as a reference basis for more sophisticated molecular biologic analyses of the causative factors of disc aging or premature aging (degeneration). A total of 180 complete sagittal lumbar motion segment slices obtained from 44 deceased individuals (fetal to 88 years of age) were analyzed with regard to 11 histologic variables for the intervertebral disc and endplate, respectively. In addition, 30 surgical specimens (3 regions each) were investigated with regard to five histologic variables. Based on the semiquantitative analyses of 20,250 histologic variable assessments, a classification system was developed and tested in terms of validity, practicability, and reliability. The classification system was applied to cadaveric and surgical disc specimens not included in the development of the classification system, and the scores were assessed by two additional independent raters. A semiquantitative analyses provided clear histologic evidence for the detrimental effect of a diminished blood supply on the endplate, resulting in the tissue breakdown beginning in the nucleus pulposus and starting in the second life decade. Significant temporospatial variations in the presence and abundance of histologic disc alterations were observed across levels, regions, macroscopic degeneration grades, and age groups. A practicable classification system for age-related histologic disc alterations was developed, resulting in moderate to excellent reliability (kappa values, 0.49-0.98) depending on the histologic variable. Application of the classification system to cadaveric and surgical specimens demonstrated a significant correlation with age ( < 0.0001) and macroscopic grade of degeneration ( < 0001). However, substantial data scatter caution against reliance on traditional macroscopic disc grading and favor a histology-based classification system as a reference standard. Histologic disc alterations can reliably be graded based on the proposed classification system providing a morphologic framework for more sophisticated molecular biologic analyses of factors leading to age-related disc changes. Diminished blood supply to the intervertebral disc in the first half of the second life decade appears to initiate tissue breakdown.

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Author and article information

Journal

Journal ID (nlm-ta): Int J Med Sci

Journal ID (iso-abbrev): Int J Med Sci

Journal ID (publisher-id): ijms

Title: International Journal of Medical Sciences

Publisher: Ivyspring International Publisher (Sydney )

ISSN (Electronic): 1449-1907

Publication date Collection: 2020

Publication date (Electronic): 24 February 2020

Volume: 17

Issue: 5

Pages: 685-692

Affiliations

[1 ]Department of Orthopedic, Xijing Hospital, Fourth Military Medical University. Western Changle Road, Xi'an, 710032, Shannxi Provence, P. R. China.

[2 ]Department of Radiology, Xijing Hospital, Fourth Military Medical University. Western Changle Road, Xi'an, 710032, Shannxi Provence, P. R. China.

Author notes

✉ Corresponding author: Zhuo-Jing Luo. E-mail: zjluo@ 123456fmmu.edu.cn ; FAX: +86 29 84775285; Phone: +86 29 84775285.

#These authors contributed equally to this work.

Competing Interests: The authors have declared that no competing interest exists.

Article

Publisher ID: ijmsv17p0685

DOI: 10.7150/ijms.42238

PMC ID: 7085207

PubMed ID: 32210719

SO-VID: 7c1cc24c-301e-4587-ae42-fa87bc7ed992

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This is an open access article distributed under the terms of the Creative Commons Attribution License ( https://creativecommons.org/licenses/by/4.0/). See http://ivyspring.com/terms for full terms and conditions.

The Immune Privilege of the Intervertebral Disc: Implications for Intervertebral Disc Degeneration Treatment

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International Journal of Applied Technology in Medical Sciences

Most cited references 80

Role of cytokines in intervertebral disc degeneration: pain and disc content.

Disc in flames: Roles of TNF-α and IL-1β in intervertebral disc degeneration.

Classification of age-related changes in lumbar intervertebral discs: 2002 Volvo Award in basic science.

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