Specific Response of the Immunoglobulins to Rubella Infection ∗

Abstract

The teratogenic consequences of rubella infection early in pregnancy are well known. However, experience with the rubella epidemic in 1964 revealed unexpected virologic and serologic consequences of maternal infection. Despite the fact that the rubella syndrome was caused by maternal infection prior to the immunologic maturity of the fetus, serologic immunity rather than tolerance was observed in older children with the syndrome (1, 2). Furthermore, rubella virus was found to persist in the affected infants for many months despite the presence of serum antibodies (3-5). Attempts to equate the presence of rubella antibodies in these infants with an active immune response by means of conventional serology was complicated by the presence of passively acquired maternal antibodies of the IgG variety which persist for several months. Since IgA and IgM do not cross the placental barrier readily, the association of antibody activity within the IgM and/or IgA class of globulins of the infant's serum would indicate active immunity. The following studies were carried out in order to characterize the classes of immunoglobulin which responded specifically to rubella infection and to determine their chronology. Observations were also made regarding the classes of rubella antibodies in sera from “normal” newborns and infants with congenital rubella.

Materials and Methods. Rubella antibodies were demonstrated by the indirect fluorescent antibody method as described by Brown et al. (6). Whereas conventional methods of serum fractionation and antibody titration were cumbersome, this technique provided a rapid and reliable method for identification of the antigenic class of antibodies (IgG, IgA, or IgM) in whole serum which had combined with viral antigen. Cover slip cultures of a chronically infected line of monkey kidney cells (7) fixed in acetone were employed as an antigen source. The conjugated antisera used in this study were purchased from Hyland Laboratories as fluorescein conjugated antisera prepared in goats against human IgG, IgA, and IgM globulins, respectively. Before use these sera were fractionated by DEAE chromatography as described by Riggs et al. (8).