Morphological study of lectin binding in the rabbit temporomandibular joint disc

Glycoconjugates of the extracellular matrix are important for the normal mechanical functions of connective tissue structures such as the temporomandibular joint disc. Since lectins are known to bind to sugar residues with high affinity, a variety of lectins were used to study the presence and distribution of glycoconjugates in the temporomandibular joint disc. Discs were removed from 6 to 8-month-old rabbits and either sectioned in a cryostat and processed for light microscopy or fixed in 2% glutaraldehyde and processed for electron microscopy. The frozen sections were incubated with fluorescein- or peroxidase-conjugated lectin solutions. Ultrathin sections mounted on grids were incubated with lectins combined with a colloidal gold marker system for electron microscopical study. Our results indicate that Canavalia ensiformis agglutinin (ConA) showed little or no binding to the discal tissue. Triticum vulgaris agglutinin (WGA) and Maclura pomifera (MPA) were bound strongly to both the synovium and the extracellular matrix and WGA also bound to the territorial matrix of chondrocyte-like cells. Glycine max and Arachis hypogoea agglutinins (SBA and PNA), were localized in the synovium and extracellular matrix but to a lesser degree than WGA and MPA. WGA, MPA, Griffonia simplicifolia II and Ulex europaeus were bound by discal fibroblasts. WGA was also localized in lysosomes of synovial A-cells (macrophages). The electron microscopical studies with lectins and colloidal gold marker systems indicated that some areas of the disc may be fibrocartilagenous as had been suggested by earlier immunohistochemical studies using monoclonal antibodies to characteristic glycosaminoglycans (GAGs) in cartilage.