Characterization of macrophage trafficking to and accumulation in livers after rIFN-α treatment. Bone marrow leukocytes from untreated 129-IFN-α/βR⁺ or 129-IFN-α/βR^– mice were fluorescently labeled as described in Methods. Cells were transferred intravenously to IFN-α/βR⁺ or IFN-α/βR^– recipients that were treated with vehicle or rIFN-α and examined. Sections shown are from an rIFN-α–treated IFN-α/βR⁺ recipient after transfers from untreated IFN-α/βR⁺ donors (a), an rIFN-α–treated IFN-α/βR^– recipient after transfers from untreated IFN-α/βR⁺ donors (b), an rIFN-α–treated IFN-α/βR⁺ recipient after transfers from untreated IFN-α/βR^– donors (c), and an rIFN-α–treated IFN-α/βR^– recipient after transfers from untreated IFN-α/βR^– donors (d). Scale bar = 100 μm. Liver leukocytes were prepared from recipient mice and analyzed by flow cytometry. Numbers of donor-derived PKH26⁺ and PKH26⁺F4/80⁺CD11b⁺ cells g liver are shown (e). *Difference between vehicle- and rIFN-α–treated IFN-α/βR⁺ recipients is significant at P < 0.001. To characterize the accumulation of migrating macrophages, liver leukocytes were obtained from IFN-α/βR⁺ or IFN-α/βR^– mice that were treated with vehicle or rIFN-α, labeled with F4/80 and CD11b and examined by flow cytometry. Migrating populations were identified by analyses of CD11b expression after gating on the F4/80⁺ cells (f). Representative histograms are shown, with thick lines representing isotype control antibody and shaded histograms F4/80 or CD11b labeling. Percentages of F4/80⁺CD11b⁺ macrophages per g liver isolated from vehicle- (black bar) or rIFN-α–treated (gray bar) samples are shown (g). In all experiments, data represent the means ± SE (n = 3). *Difference between vehicle control and rIFN-α treatments is significant at P ≤ 0.02.