Confirmation of Macrophage Cell Depletion Examined in the Spleens of Liposome-Treated Animals. A-B) 1 week after liposome administration no macrophage cells were present in the spleens of treated animals, as confirmed by the absence of CD68 (macrophage marker) immunoreactivity (***P < 0.0001; I). C-D) By 2 week after liposome treatment completion, macrophage cells (CD68+) had already began to repopulate in the spleen of treated animals (*P < 0.05; I). E-F) At the end of the experimental period (day 35) macrophage numbers in the spleen of treated animals had returned to normal levels, as compared to untreated animals (G-H). I) Quantification of immunoreactive CD68+ cells as shown in panels A-H, demonstrated a significant cellular reduction during liposome administration and during repopulation 2 weeks after treatment completion. No differences in macrophage cells were found at the end of the study. Columns represent an averaged mean (5 sections per animal, n = 5) and error bars indicate error of mean (+/- S.E.). Scale bars A, C, E, G 500 μm, enlarged views B, D, F, H 200 μm.