Macrophage efflux to the lymphatic system and to the blood circulation. (A) The GFP⁺ peritoneal macrophages, obtained from the GFP transgenic mice, were injected into the peritoneum of TG-preconditioned WT mice (5 × 10⁶ GFP⁺ cells per mouse). At different time points after LPS stimulation, the draining lymph nodes were collected and cyrofixed. The presence of the GFP⁺ macrophages within the frozen sections of the fixed lymph nodes was visualized by fluorescence microscopy (objective lens 100 ×). (B) Additionally, leukocytes were recovered from different lymph nodes of the same mice that were treated with PBS (▪) or LPS (○) for 4 hours, and the number of the GFP⁺ cells retrieved was determined by hemocytometer. The data shown are the mean ± SD (n = 3). (C) Total blood samples were taken at different time points from mice in panel A and analyzed for the presence of the GFP⁺ macrophages by FACS analysis. Representative data of 2 independent experiments are shown. ^*PBS versus LPS P < .001.