Identification of heterogeneous cell populations in normal human intervertebral disc

There is clear evidence that tissues related to the intervertebral disc, such as articular cartilage, contain several phenotypically different chondrocytic cell populations. Histological data for the disc suggest 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 bead culture system for up to 6 wk. The cells remained viable and produced matrix, but did not divide. Cultured cells were stained simultaneously for the presence of chondroitin sulphate and keratan sulphate, or types I and II collagen. The majority of the cells from both the annulus 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 indication of a population of cells with a nonchondrocytic phenotype. In nondegenerative discs, the majority of the annulus fibrosus cells produced both types I and II collagen but the majority of nucleus pulposus cells produced only type II collagen. These observations are consistent with the presence of at least 2 phenotypically stable populations of cells in the adult human intervertebral disc and with the view that the phenotype of the major population of the annulus is different from that of the nucleus.