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Abstract

Objective

The expression of proinflammatory factors such as tumor necrosis factor α (TNFα), interleukin-6 (IL-6), IL-8, and prostaglandin E2 (PGE2) is significantly correlated with the symptoms of herniated disc disease. Among the different types of immune cells, macrophages are frequently noted in the herniated disc tissue. We undertook this study to clarify the interaction of the intervertebral disc (IVD) and macrophages with regard to the production of TNFα, IL-6, IL-8, and PGE2.

Methods

We developed 2 animal models to assess the interactions of IVDs with macrophages in terms of TNFα, IL-6, IL-8, and PGE2 production and pain-related behavior. We also cocultured IVDs and macrophages to assess the role of TNFα in IL-6, IL-8, and PGE2 production.

Results

IVD autografts induced TNFα, IL-6, IL-8, and cyclooxygenase 2 (COX-2) messenger RNA (mRNA) up-regulation; macrophage infiltration was seen shortly after the autograft was implanted. A significant decrease was noted in the mechanical threshold of the ipsilateral paw following the up-regulation of TNFα, IL-6, IL-8, and COX-2 mRNA. Only IVD and macrophage cocultures resulted in IL-8 and PGE2 up-regulation. TNFα up-regulation was maximized before that of IL-6 and IL-8. TNFα neutralization attenuated production of IL-6 and PGE2, but not that of IL-8. Neutralization of TNFα and IL-8 significantly increased the paw withdrawal mechanical threshold in the IVD autograft and spinal nerve ligation model.

Conclusion

IVD–macrophage interaction plays a major role in sciatica and in the production of TNFα, IL-6, IL-8, and PGE2. TNFα is required for IL-6 and PGE2 production, but not for IL-8 production, during IVD–macrophage interaction. Neutralization of TNFα and IL-8 can be a valuable therapy for herniated disc disease.