Chemokine profile of herniated intervertebral discs infiltrated with monocytes and macrophages

Study Design. Herniated lumbar disc specimens were analyzed using reverse transcriptase-polymerase chain reaction to determine the profile of chemokine expression. Objective. To investigate the mechanism underlying the recruitment of inflammatory cells into herniated discs during the process of spontaneous regression. Summary of Background Data. Spontaneous regression of herniated intervertebral discs has been increasingly reported. Although macrophages are suggested to play a central role in this process, it remains unclear how these macrophages accumulate in the herniated discs. Methods. RNA was extracted from 36 surgical specimens of the herniated lumbar disc, a disc specimen of idiopathic scoliosis and pyogenic spondylitis, and activated peripheral blood mononuclear cells of a normal donor. The RNA was reverse transcribed, and the resultant cDNA was amplified by PCR using primer pairs specific to the CXC chemokines (IL-8, MGSA-alpha, IP-10, MIG), the CC chemokines (MCP-1, MCP-2, MCP-3, MCP-4, MIP-1alpha, MIP-3alpha, RANTES, STCP-1), the C chemokine (lymphotactin), and the glyceraldehyde phosphate housekeeping gene. Thin cryostat sections also were made from the disc specimens and stained with hematoxylin and eosin. Results. All the chemokines examined except MCP-4 were expressed by activated peripheral blood mononuclear cells. Glyceraldehyde phosphate was detected in 8 of 36 herniated discs and in 1 disc specimen each of idiopathic scoliosis and pyogenic spondylitis. Chemokine expression was examined for these 10 disc specimens. From among the 13 chemokines examined, MCP-3, MCP-4, RANTES, and IP-10 were detected in the disc from the idiopathic scoliosis and MCP-3, MCP-4, RANTES, IP-10, MIG, and MGSA-alpha were detected in the infected or herniated discs. Histologic analysis showed infiltration of inflammatory cells in the infected disc and all 8 herniated discs. Conclusions. The findings suggest that chemoattractive properties exist in a selected population of human intervertebral discs, and that unique sets of chemokines play a role in spontaneous regression of these herniated disc tissues.