Increased multiplication of dengue virus in mouse peritoneal macrophage cultures by treatment with extracts of Ascaris-Parascaris parasites.

Methylcellulose-elicited peritoneal macrophages from BALB/c mice were cultivated in vitro and inoculated with dengue virus (DV). At intervals thereafter portions of the culture fluids were taken and titrated for viral infectivity. Extracts from Ascaris suum and Parascaris equorum, either crude or Sephadex G-100 fractionated, were examined for effects on the multiplication of DV. The macrophage cultures treated with the above substances produced larger amounts of DV compared with untreated control cultures. The enhancing effect of the substances depended on doses added and duration of treatment and was suppressed by co-treatment with carrageenan, a specific macrophage-inhibiting agent, but was not related to the viability of cultured cells. In fluorescent antibody (FA) as well as infectious center assay experiments, it was shown that the DV-infected cells were found more frequently in treated cultures than in untreated control cultures. In the treated cultures phagocytosis by cultured cells was also of a higher magnitude than that in untreated cultures. In cocultures of macrophages and splenocytes from the same line of mice, no additive effect of splenocytes was noted. The limulus amebocyte lysate clotting enzyme reaction (Limulus test) indicated that involvement of bacterial lipopolysaccharides in the enhancement phenomena was negligible. The data so far obtained suggest that the enhancing effect was due to direct action of the parasitic extracts on macrophages. Four Sephadex G-100 fractions from the crude extracts showed similar activities; however, the effects of fractions I and III appeared to be comparatively strong. Significance of the findings in relation to the pathogenesis of DV infection was discussed.