Synthesis of RNA by Normal Mouse Spleen Cells after Stimulation with Antigen in vitro

Abstract

TREATMENT of animals or tissue cultures with antimetabolites¹ or irradiation² during the first few hours after antigenic stimulation profoundly affects the immune response. Dutton and Mishell^3,4 reported that “hot” pulses of tritiated thymidine were lethal to proliferating antibody-forming cells when added to dissociated spleen cell cultures stimulated with sheep erythrocytes in vitro. Pulses given 24–32 h after antigen were lethal, whereas those given before were not. This suggested that little or no DNA synthesis occurred before 32 h in cells stimulated by antigen. We used the same approach to investigate the effects of “hot” pulses of tritiated uridine (³H-UR) to determine when antibody-forming cells and their precursors were actively synthesizing RNA. (Exogenous uridine is incorporated into the RNA of mouse tissues in vitro⁵.) We found that active RNA synthesis occurs during the first 24 h after antigenic stimulation as well as after 24 h, when active DNA synthesis occurs.