Immune Response in Dengue-2 Vaccine Recipients Measured by Two Different Radioimmunoassay Methods

Abstract

Sera from human volunteers inoculated with an attenuated dengue-2 (DEN-2) vaccine (PR-159/S-1) contained antibodies that were detected by two different radioimmunoassays. A "single sandwich" radioimmunoassay required purified DEN-2 virions for optimal reactivity but was 10 to 500 times more sensitive than neutralization or hemagglutination inhibition tests. A "double sandwich" radioimmunoassay was able to utilize crude antigens from either DEN-infected mouse brains or Aedes albopictus cell culture supernatants. When the two radioimmunoassay techniques were compared, the "single sandwich" method appeared as the better assay for IgG, while the "double sandwich" method was more sensitive for IaM detection. Selected human sera were examined for IgG, IgM and IgA responses using both techniques at various intervals following immunization. Although there were differences in magnitude, yellow fever immune as well as flavivirus non-immune volunteers responded to DEN-2 vaccination by demonstrating IgG, IgM and IgA antibody responses. In the non-immune group, the most abundant immunoglobulin detected was IgM while, in the yellow fever immune group, the predominate post-DEN-2 vaccine immunoglobulin was IgG. DEN-2-specific neutralizing antibodies were associated with either IgM or IgG according to the immune status of the volunteer. All classes of immunoglobulins attained maximum levels between 21 and 60 days post vaccination. In the majority of volunteers, IgM responses were relatively transient and could not be detected six months post immunization while IgG and IgA antibodies were still detectable after this period. Both procedures, "the single sandwich" and "double sandwich" radioimmunoassays, are sensitive immunological tests that can be used to measure specific immunoglobulin responses after DEN-2 vaccination. Immunoglobulin levels can be measured directly, eliminating the need to purify these immunoglobulins prior to assay.