Distribution and biosynthesis of connective tissue components by synovial fibroblasts cultured with mononuclear inflammatory cells.

Two main cell types, spindle-shaped and large flattened cells, were identified in fibroblast cultures from synovial tissue explants. Type I collagen and fibronectin were visualized by indirect immunofluorescence and the hyaluronic acid coat around the cells by the erythrocyte exclusion method. Collagen was detected as intracellular granules which varied greatly in their number with no correlation to the cell shape. Hyaluronic acid coat was seen only around the spindle-shaped cells, whereas the intercellular fibronectin was found throughout the cultures. Morphological alterations in synovial fibroblasts were detected when subjected to mononuclear cells isolated from peripheral blood. The fibroblast became thinner and branched and stellate cells with numerous extensions appeared. Hyaluronic acid synthetase activity increased by about 50% and was obviously related to the appearance of the stellate cells, whereas no evident change was detected in collagen synthesis. The stellate cells were full of collagen granules. The hyaluronic acid coat around these cells did not differ from that around normal spindle-shaped cells. Synovial fibroblasts cocultured with mononuclear cells lost the intercellular fibronectin network, but other main cell surface glycoproteins studied with the periodate-borohydride method and electrophoresis remained unaltered in spite of morphological alterations.