On the reactions of human synovial cells exposed to homologous leucocytes in vitro.

Human synovial cells were exposed in culture to leucocytes from unrelated donors and to hyaluronidase, separately and together. Polymorphonuclear leucocytes rapidly lowered pH and severely damaged the synovial cells. Lymphocytes carefully freed from PMN-stimulated synovial cell growth or, at the worst, depressed it slightly. Hyaluronidase alone tended to stimulate cell growth whereas lymphocytes and hyaluronidase together were often cytotoxic after latent periods of 48–72 hr. The stimulating and inhibitory effects of lymphocytes upon synovial cells depended on the ratios and on the particular pairings of the two cell types. Lymphocytes did not show blast transformation during the cytotoxic reactions. The inhibitory effects of lymphocytes combined with hyaluronidase were partially blocked by small amounts of heparin, and completely blocked by hydrocortisone. It is suggested that the potentiating action of hyaluronidase is attributable to removal of pericellular gels which thus allows the close contact necessary for cytotoxic effects of lymphocytes. Cytotoxic reactions between lymphocytes and synovial cells were incidentally found to be associated with increased glucose consumption.