S-100 protein in normal, osteoarthrotic, and arthritic cartilage.

The occurrence of the S-100 protein was studied in normal and pathological cartilage from patients with osteoarthrosis and rheumatoid arthritis. In normal cartilage all cells of the different zones exhibit immunoreactivity for this protein. An identical distribution is observed in cases of osteoarthrosis and rheumatoid arthritis. Cellular pannus tissue usually is devoid of the S-100 protein. However, if chondroid metaplasia occurs in this tissue the cells become positive for the S-100 protein. From these results it is concluded that a chondroid metaplasia not only leads to a matrix comparable to cartilage but also contains cells that gain further characteristics of original chondrocytes.