CONDITIONED MEDIUM FROM ACTIVATED RAT MACROPHAGES AND THE RECOMBINANT FACTORS, IL-1-BETA AND GM-CSF, ENHANCE THE ACCESSORY ACTIVITY OF DENDRITIC CELLS

Low density lymph node cells (LD-LNC; 5 % of total unfractionated LNC) contain 95 of the accessory activity required for responses of T lymphocytes to mitogens. Significantly greater responses to mitogens occur when T lymphocytes are added to LD-LNC that have been exposed overnight to silica, in comparison to responses occurring with LD-LNC incubated without silica. Conditioned medium (CM) from, silica-treated LD-LNC is itself able to mediate enhanced responses; i.e., when LD-LNC are exposed overnight to CM alone and mitogen-treated T lymphocytes added the next day. The enhancing activity found in CM from LD-LNC exposed to silica is produced by macrophages; however, their low accessory activity is not enhanced by CM. In contrast, dendritic cells isolated from LD-LNC exposed to silica or to. CM show significantly increased accessory activity, but dendritic cells do not produce the enhancing activity found in CM. CM lacks IL-2 activity and does not have any effect on the responses of untreated or mitogen-treated T lymphocytes alone. Thus, macrophages produce the enhancing activity and dendritic cells respond to it. Maximum enhancement of dendritic cell accessory activity requires overnight exposure to CM; once induced, accessory activity is not further modulated after continued incubation in the presence or absence of CM. LD-LNC, adherent peritoneal exudate cells, and adherent thioglycollate-induced peritoneal exudate cells produce enhancing activity after exposure to silica, LPS, and silica plus LPS. After gel filtration of a CM produced by silica plus LPS, enhancing activity shows a broad molecular weight distribution between 20 and 55 kD. IL-1 is present in CM and shows a more narrow molecular weight distribution that falls within the lower molecular weight range for enhancing activity. Silica treatment by itself produces CM containing little IL-1, but abundant enhancing activity; gel filtration of this CM shows that the distribution of enhancing activity is confined more narrowly to the higher molecular weight range, suggesting that IL-1 is one of several factors that enhances the accessory activity of dendritic cells. Recombinant human IL-1β does have enhancing activity, but of the other recombinant factors tested only mouse GMCSF also has enhancing activity. Human IL-1α, tumor necrosis factor α, IL-4, rat IL-3 and rat IFN-γ, as well as L cell-conditioned medium containing M-CSF, lack enhancing activity. © 1990, Gustav Fischer Verlag · Stuttgart · New York. All rights reserved.