Flow Cytometric Analysis of in Vivo Activation of Murine Spleen Cells

The in vivo effects of two polyclonal immune stimulators were studied in several strains of mice by analyzing the percentages of cells in various phases of the cell cycle by flow cytometry. Both lipopolysaccharide (LPS) and polyriboinosinic X cytidylic acid (rI X rC) were capable of inducing an increase in the percentage of cells undergoing DNA synthesis (S phase) in the spleens of several mouse strains. The response to both LPS and rI X rC was maximal between days 3 and 5 following injection. Optimal in vivo responses to LPS occurred at 3-30 micrograms, and to rI X rC at 100 micrograms; however, responses were observed over a broad dose range. No similar increase in S-phase cells was observed following injection of non-mitogenic T-independent antigens. Specific antibody was also measured after in vivo administration of rI X rC. There was a dissociation between the ability of an injection to induce specific antibody and to induce proliferation. These studies extend our knowledge of in vivo lymphocyte activation, and provide a basis for a detailed analysis of lymphocyte activation following a variety of immune modulators in vivo.