Induction of colony-stimulating factors by Plasmodium cynomolgi components

Plasmodium cynomolgi total parasite antigens soluble in culture medium (P.c.SA), when injected in monkeys (Macaca mulatta) intravenously, induced the synthesis and secretion of serum colony-stimulating factors (CSFs). In vitro cultured monkey splenic macrophages and blood monocytes, following incubation with P.c.SA, also elaborated CSFs: the splenic macrophages responded more. Peak CSFs levels, both in vivo and in vitro, were attained after 8 hours of P.c.SA stimulation, and thereafter declined to baseline values within 48 hours. CSFs, both in serum and in conditioned medium, induced the formation of macrophage, granulocyte and granulocyte-macrophage colonies in vitro, in the same proportion, indicating that committed progenitor cells responded to CSF from both sources in a similar way. Polymyxin B treatment had no effect on P.c.SA stimulated CSF elaboration by macrophages, suggesting an LPS-independent mechanism of CSF induction. CSF synthesis appeared to be de novo, as cycloheximide treatment of macrophages completely inhibited CSF production. These observations indicate that P. cynomolgi components can induce CSF synthesis.