Bovine monocytes and macrophages: an accessory role in suppressor-cell generation by Con A and in lectin-induced proliferation.

Non-specific suppressor-cell activity was generated in bovine peripheral-blood leucocytes by treatment with various concentrations of concanavalin A. The activity was expressed against syngeneic and allogeneic responder cells. The involvement of the macrophage-monocyte was found to be necessary for the induction of suppressor cells. After depletion of monocytes from peripheral-blood leucocytes, by sequential plastic adherence and passage through Sephadex G-10 columns, the inducible suppressor activity was significantly reduced or completely abolished. Reconstitution with monocytes resulted in renewed activity in a dose-dependent manner. Histocompatibility identity of macrophages and non-adherent cells was not required since allogeneic macrophages reconstituted the response of non-adherent cells to a degree comparable to syngeneic cells. Alveolar macrophages were shown to be even more efficient as accessory cells for suppressor-cell induction than peripheral-blood monocytes.