Properties and Antigenic Relationships of Hemagglutinins Associated with the Dengue Viruses

Summary Hemagglutinins for chick erythrocytes were recovered from the brains of suckling mice infected with the 7th or 118th mouse passages of the Type 1, Hawaii strain or with the 19th mouse passage of the Type 2, New Guinea “C” strain. The 2 antigenically distinct, but related dengue hemagglutinins can be distinguished by the pH requirements for reaction and for maximum titers of hemagglutination. Immediately after extraction of the brains with pH 9 borate buffer, the Type 2 hernagglutinin was demonstrable when the erythrocytes were allowed to sediment at 4 C (only at pH 6.5–6.7) but not at 20–25 C, while the Type 1 hemagglutinin, regardless of mouse passage levels, was demonstrable at both temperatures in a broader pH zone (6.2–7.5 with maximum titers in the range of 6.7). Both hemagglutinins rapidly deteriorated at pH 6.7 at 4, 25, and 37 C, and paradoxically inactivation seemed to occur faster at 4 C than at 25 C. At pH 7.0–7.9 there was marked stability at 4 C and 25 C with all preparations, regardless of mouse passage level, while at 37 C the 19th mouse passage Type 2 and 7th mouse passage Type 1 preparations remained stable for at least 18 hours, while the 118th mouse passage Type 1 hemagglutinin lost almost all its potency in 1 hour. The hemagglutinins remained stable at pH 7.9 at 4 C for at least 4 months, while freezing at about -80 C and thawing completely destroyed their activity. Specific hemagglutination-inhibition (H-I) antibody was readily separated from normal inhibitor in human, monkey and rabbit sera by precipitation with acetone. Higher H-I titers were obtained when antibody and hemagglutinin at pH 7.7 were incubated for 2 hours at 22 C, prior to the addition of the erythrocytes (suspended in buffer pH 5.6 to bring the mixture to pH 6.7 which was optimum for hemagglutination). Dengue antisera which were strictly homotypic by the neutralization test reacted to varying titers with the heterotypic dengue hemagglutinin. By means of the H-I tests the dengue viruses were shown to be antigenically related to the St. Louis, Japanese B, West Nile and yellow fever viruses but not to those of sandfly fever, Rift Valley fever, or Western equine encephalitis.