Accessory cells distinct from macrophages in lymphocyte proliferation of cynomolgus monkeys

Mononuclear cells of cynomolgus monkeys were separated into four distinct fractions based on their buoyant density on discontinuous gradients of Percoll. Cells of the lightest density (fraction I) were enriched for macrophages and B cells, whereas cells from the denser fractions (fractions II-IV) consisted mainly of T cells, especially in fraction IV up to 88%. Cells of moderate density (fractions II and III) could respond better to T cell mitogens than unfractionated cells. In contrast, cells of fraction I not only failed to respond to mitogens, but also exerted an inhibitory effect on lymphocyte proliferation, indicating that macrophages might suppress the response in cynomolgus monkeys. Cells alone having the heaviest density (fraction IV), although enriched for T cells, also showed no significant response. However, addition of mitomycin C-treated fraction II or III resulted in partial restoration in the proliferative response of this fraction. Further examination revealed that the accessory activity resided in the non-adherent, nonphagocytic, non-E rosette-forming and Fc receptor-negative cells with moderate density, suggesting the presence of accessory cells distinct from monocyte/macrophage lineage in cynomolgus monkeys.