DNA synthesis in subpopulations of blood mononuclear leucocytes in human subjects after vaccination against yellow fever.

After vaccination of five volunteers with yellow fever live vaccine, blood mononuclear cells were isolated and labelled with 3H-thymidine at intervals. DNA synthesis was measured by scintillation counting and autoradiography of rosetted cells. Rosetting with sheep erythrocytes (E-RFC) identified T cells, and such erythrocytes coated with IgM antibodies and complement (EAC-RFC) identified B cells and monocytes. DNA synthesis in the total mononuclear cell fraction, as well as in subfractions enriched in or deprived of E-RFC, displayed a sharp increase on day 10--11 after vaccination, remained high on day 13--14, and then returned to the prevaccination level. There was a corresponding morphological transformation, measured by size distribution and number of nucleoli per cell. The major fraction of DNA-synthesizing cells before, during and after the peak of activity was found among non-rosette-forming cells. However, during the activity peak the numbers and proportion of DNA-synthesizing E-RFC were increased while the response with regard to EAC-RFC was not obvious. Thus within a complex cellular response a transient T-cell response was identified.