Role of macrophages in the transmission of dengue virus-induced suppressor signal to a subpopulation of T lymphocytes.

In dengue type 2 virus (DV)-infected mice, the virus-specific immunosuppression is mediated by a two-step mechanism: (1) induction of T suppressor cells (Ts1) by by virus to produce a suppressor factor (SF) which (2) stimulates another subpopulation of T cells (Ts2) to produce prostaglandin which finally mediates suppression. SF suppresses DV-specific IgM plaque-forming cells (PFC) in the spleen cells sensitized in vivo or in vitro, as detected by Jerne's haemolytic plaque technique. The present study enabled us to investigate the role of an intermediary cell in transmission of the suppressor signal from Ts1 to Ts2. It was observed that SF was adsorbed on the surface of peritoneal macrophages. Live macrophages adsorbed SF, retrieved it from that adsorbed on heat-killed macrophages and presented it to the target cells. Heat-killed macrophages adsorbed SF to the same extent as live ones, but could present it to the target cells by themselves. The target cells of SF were unprimed splenic T lymphocytes. SF suppressed DV-specific PFC in syngeneic spleen cells and was adsorbed on syngeneic macrophages, but not on those from allogenic animals. The findings described here show that the presence of live macrophages is obligatory for transmission of the suppressor signal to the target Ts2.