Commitment to deoxyribonulceic acid synthesis and the cell cycle in endotoxin-stimulated murine spleen cells

Events associated with endotoxin-induced mitogenesis in murine spleen cells were investigated. Commitment to deoxyribonucleic acid (DNA) synthesis, the onset of DNA synthesis, and phases of cell cycle were timed. Increased levels of DNA synthesis in murine spleen cells stimulated with endotoxin were observed 12 to 16 h after the addition of the mitogen. The total cell cycle time of stimulated B-cells was 11 to 14 h. The S-phase was 8 h. The G2-phase was 1 h, and the combined M-plus G1-phase of cycling cells was 2 to 5 h. A 1- to 4-h exposure to lipopolysaccharide elicited a significant increase in DNA synthesis. Progressively longer exposures to lipopolysaccharide, up to 24 h, produced further increases in first-cycle DNA synthesis. Polymyxin B, when added with endotoxin to cultures from the outset, inhibited first-cycle DNA synthesis. However, if addition of the antibiotic was delayed, progressive increases in first-cycle dna synthesis were observed. These data indicate a heterogeneity among B-cells in their responsiveness to endotoxin.