Proteoglycan components of the intervertebral disc and cartilage endplate: an immunolocalization study of animal and human tissues.

Monoclonal antibodies have been used to study the presence and distribution of various components of the proteoglycan molecule in the intervertebral disc and cartilage endplate. Link protein, hyaluronic acid binding region, keratan sulphate and chondroitin 4- and 6-sulphate have been investigated in tissues from humans and other mammals. Exposure of the carbohydrate and protein epitopes was enhanced by chondroitinase and trypsin pretreatment respectively. The degree of immunoreactivity varied with location, being greater in the nucleus pulposus than the annulus fibrosus with least reactivity in the cartilage endplate. In addition, there was increased staining in the pericellular domains, particularly in adult tissues. Areas of ectopic calcification exhibited very different immunoreactivity, depending on the type of calcium salt present. Calcium hydroxyapatite deposits showed greater staining for 8A4 (link protein), while calcium pyrophosphate deposits demonstrated greater staining for 3B3(-), 7D4(-) and 3D5 than the surrounding non-calcified matrix. Staining for chondroitin sulphate isomer epitopes 3B3(-) and 7D4(-), indicative of modified chondroitin sulphate chains, was greater in human tissues of degenerate than non-degenerate appearance. This suggests that expression of these epitopes may be an indicator of disease and subsequent reparative procedures in intervertebral disc and cartilage endplate, similar to that seen in articular cartilage degeneration.