Cell cluster formation in degenerate lumbar intervertebral discs is associated with increased disc cell proliferation

Healthy human intervertebral discs contain relatively few cells and these a re sparsely distributed. A characteristic feature of disc degeneration, how ever, is the appearance of cell clusters, particularly in damaged areas. Ho w these clusters form is currently unknown. We have examined excised pathol ogical human discs for evidence of cell proliferation. Disc sections were i mmunostained for the proliferating cell nuclear antigen (PCNA) and the prol iferation-associated Ki-67 antigen. PCNA immunopositive cells were observed within degenerate discs, commonly though not exclusively, in cell clusters . Cells immunopositive for the Ki-67 antigen were less prevalent than those for PCNA, but similarly were observed frequently within clusters in degene rate discs. In contrast, immunopositivity for these markers was not common in less degenerate discs or in areas of the disc where cell clusters were n ot observed. These observations suggest that disc cell proliferation is ass ociated with disc degeneration and is the likely cause of cell cluster form ation.