Effect of urea on the hemagglutinating and complement-fixing antigens of type 2 Dengue virus.

Sephadex G-200 filtration was used for fractionating dengue type 2 (DEN-2)-infected suckling mouse brain (SMB) supernatant fluids. The high-molecular-weight fraction, which was eluted in the void volume, showed no increase in type specificity when tested against immune ascitic fluid to the four prototype dengue viruses. A void-volume fraction obtained after the infected SMB supernatant fluids were treated with urea displayed significant increases in complement fixation (CF) type specificity. Immune ascitic fluid prepared against the more typespecific DEN-2 antigen demonstrated neutralizing ability and greater CF type specificity. When DEN-2 sucrose-acetone-extracted hemagglutinating (HA) antigens were treated with 6 m urea at 37 C for various time intervals, all HA antigen was destroyed in 15 min. Urea treatment of infected SMB supernatant fluids indicated that the CF antigens were more stable to the effect of urea than were the HA antigens. After urea treatment of the SMB supernatant fluids, the CF type specificity increased as the hemagglutination inhibition titer decreased.