Suppression of the Response of Lymphocytes to Phytohemagglutinin in Rubella

The response of lymphocytes to phytohemagglutinin after rubella vaccination was studied by measurement of mitotic rates and uptake of tritiated thymidine in lymphocyte cultures. Immunization with 25th-passage rubella virus (M-33 strain) caused statistically significant suppression of mitosis 11 days after inoculation, with a return to normal by day 20. Antibodies to rubella virus appeared between day 14 and day 17. Rubella vaccines RA27/ 3 or HPV77-DE5 did not induce uniform changes in mitotic response to phytohemagglutinin, although reduced mitotic indices were detected in individual cases on day 8 or day 14. However, transient suppression of the phytohemagglutinin response was demonstrated by thymidine uptake in one of the vaccinated groups (RA27/3). In vaccinees who seroconverted there was no clear correlation between the return of the phytohemagglutinin response and the appearance of rubella antibodies. These results confirm that rubella infection causes temporary suppression of lymphocyte responsiveness to phytohemagglutinin and suggest that attenuated strains of rubella vaccine virus are less immunosuppressive (by this measure) than unattenuated rubella virus.