IDENTIFICATION OF HETEROGENEOUS CELL-POPULATIONS IN NORMAL HUMAN INTERVERTEBRAL DISC

There is clear evidence that tissues related to the intervertebral dis c, such as articular cartilage, contain several phenotypically differe nt chondrocytic cell populations. Histological data for the disc sugge st the same may be true for the annulus fibrosus and nucleus pulposus, but this has not been shown directly. For the first time, cells from adult human nondegenerative nucleus pulposus and annulus fibrosus were recovered after enzymatic digestion and maintained in an alginate bea d culture system for up to 6 wk. The cells remained viable and produce d matrix, but did not divide. Cultured cells were stained simultaneous ly for the presence of chondroitin sulphate and keratan sulphate, or t ypes I and II collagen. The majority of the cells from both the annulu s fibrosus and the nucleus pulposus produced both keratan sulphate and chondroitin sulphate (> 60%), a few only detectable levels of one or the other, but a significant population produced neither. This is an i ndication of a population of cells with a nonchondrocytic phenotype. I n nondegenerative discs, the majority of the annulus fibrosus cells pr oduced both types I and II collagen but the majority of nucleus pulpos us cells produced only type II collagen. These observations are consis tent with the presence of at least 2 phenotypically stable populations of cells in the adult human intervertebral disc and with the view tha t the phenotype of the major population of the annulus is different fr om that of the nucleus.