Effects of LPS on macrophage fluid phase uptake in the absence of serum. Murine clone 4-4 macrophages were washed four times with serum-free medium and stimulated with LPS for 45 minutes at 37°C in the presence of [³H]sucrose. Subsequently, the cells were placed on ice and washed, and accumulated radioactivity was determined by scintillation counting. Using the specific activity of the [³H]sucrose, fluid phase uptake was expressed as femtoliter per cells per minute. The results show the average of three independent determinations.