Expression of the ED B fibronectin isoform in adult human articular cartilage.

The most recently described region of alternate splicing of fibronectin mRNA results in expression of an isoform which includes the type III repeat termed ED B (EIII B). To date this isoform has been detected in transformed cells in culture, in the synovial membrane and ovary but in no other adult tissue, and in embryonic chick cartilage to a much greater extent than in other cells of mesenchymal origin. Monoclonal antibody BC-1, which recognizes an epitope within the ED B segment, was used in two different assays and provided evidence that adult human articular cartilage contains ED B fibronectin. The extent of expression of this isoform, however, was variable and less than that found in fibronectin produced by the transformed fibroblast cell line WI-38VA13.