Influence of macrophage infiltration of herniated disc tissue on the production of matrix metalloproteinases leading to disc resorption.

STUDY DESIGN

Herniated lumbar disc specimens were cocultured with peripheral blood mononuclear cells, and cells isolated from extruded disc were cultured to study the production of matrix metalloproteinases.

OBJECTIVE

To investigate the role of peripheral blood mononuclear cells infiltrating extruded discs and disc-derived cells in the production of matrix metalloproteinases.

SUMMARY OF BACKGROUND DATA

Magnetic resonance imaging analysis of herniated disc patients revealed a progressive decrease in the size of herniated discs. Spontaneous regression of herniated disc is associated with infiltrating macrophages, and matrix metalloproteinases have been implicated in this phenomenon. However, the correlation between infiltrating macrophages and the production of matrix metalloproteinases has received little research attention.

METHODS

Each disc specimen was incubated with homologous peripheral blood mononuclear cells. The numbers of peripheral blood mononuclear cells attached to the surfaces of herniated discs were counted and the culture media was assayed for MMP-3. The cells isolated from herniated discs were incubated with cytokines and the production of matrix metalloproteinases was measured. Total RNA was extracted from herniated discs and RT-PCR was carried out.

RESULTS

Significantly larger numbers of peripheral blood mononuclear cells were attached to the surfaces of extruded discs, and higher amounts of MMP-3 were detected than those of control discs. The culture medium of extruded discs showed higher MMP-1 and MMP-3 production than those from controls. Significant enhancement of MMP-1 and MMP-3 mRNA expression was observed in the disc-derived cells stimulated with cytokines.

CONCLUSION

These results suggest that peripheral blood mononuclear cells infiltrating extruded discs may secrete a variety of biologic materials capable of further recruiting monocytes into herniated discs in an autocrine fashion. Disc cells stimulated with cytokines showed enhanced production of matrix metalloproteinases, which might play an important role in spontaneous regression of disc materials.