Lectin-dependent and lectin-independent activities of human mononuclear cells that modulate the growth of human synovial cells.

Human peripheral mononuclear cells (MC) secrete 2 soluble activities that modulate the growth of human synovial fibroblastic cells. A growth-suppressive, lectin-dependent activity is elaborated by the non-adherent population and its secretion begins before DNA synthesis is initiated in concanavalin-stimulated MC cultures. The elaboration of this activity is partially dependent on the presence of serum and it appears to be distinct from virus-induced human leukocyte interferon. The second activity is secreted spontaneously by the MC, under a variety of culture conditions including supplementation with homologous human plasma, and it enhances the growth of synovial fibroblasts. The rate of secretion of the growth-enhancing activity by the nonstimulated MC approximately parallels that of the inhibitory activity from the stimulated MC cultures. MC from patients with rheumatoid arthritis and from nonaffected individuals secrete similar concentrations of growth-stimulatory activity for the synovial fibroblasts.