Specific immunosuppressive delay of the plaque-forming response by trace amounts of antibody of maternal origin in young rats injected with mouse or sheep erythrocytes.

Young rats do not respond to antigenic stimulation with sheep erythrocytes for the first 2 weeks of post-natal life. However, if mouse erythrocytes were used as antigen a plaque-forming cell (PFC) response was sometimes detectable as early as 4 days after birth. In order to demonstrate that undetectable trace amounts of anti-sheep antibody of maternal origin were causing the suppressive delay in PFC response to sheep erythrocytes, means of artificially suppressing the anti-mouse PFC response were studied. Hyperimmunization of pregnant rats with mouse erythrocytes resulted in the transmission of sufficient anti-mouse antibody to the offspring to bring about complete and specific suppression of their PFC response for up to 8 weeks after birth. High dilutions of IgM or IgG fractions of anti-mouse rat sera administered to 6-day-old rats 24 hours before they were injected with mouse erythrocyte antigen caused complete suppression of the relatively weak PFC response. This model can be used to detect trace amounts of antibody and is about 400 times more sensitive than conventional haemagglutination techniques.