Dengue virus multiplication in cultures of mouse peritoneal macrophages: effects of macrophage activators

Dengue-2 virus multiplied in cultures of methylcellulose-induced peritoneal macrophages of BALB/c mice. The in vitro-cultivated macrophages from dengue-1 virus-immune mice produced larger amounts of dengue-2 virus than did those from nonimmune controls. The effect of macrophage activators was examined by using nonimmune macrophages. Enhanced virus production was demonstrated in cultures of macrophagges pretreated with phytohemagglutinin (PHA) or bacterial lipopolysaccharide (LPS). The number of virus-infected cells in the pretreated cultures was estimated to be about 0.01% or less of the total macrophages. Continuous treatment of macrophages with PHA before and after virus inoculation brought about the most marked enhancement of dengue-2 virus multiplication. On the other hand, treatment with concanavalin A or pokeweed mitogen showed little effect on the multiplication of the same virus. Treatment with carrageenan, a specific macrophage blocking agent, markedly suppressed dengue-2 virus production in both dengue-1 virus-immune macrophages and LPS-treated macrophages. The indirect fluorescent-antibody (FA) technique revealed dengue-2 viral antigen in the cytoplasm of infected macrophages, and the FA-positive macrophages were more numerous in PHA-treated cultures than in untreated controls. The results obtained are discussed in relation to a possible role of activated monocytes/macrophages in the pathogenesis of dengue hemorrhagic fever.