Morphologic Detection and Functional Assessment of Reconstituted Normal Alveolar Macrophages in the Lungs of SCID Mice

Alveolar macrophages (AMs) from immunocompetent animals were isolated from bronchoalveolar lavage and labeled with the fluorescent marker 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate (DiI). These AMs were administered intratracheally into mechanically ventilated SCID mice. From 1 to 28 days later, the recipient mice underwent bronchoalveolar lavage to isolate their AMs. To determine whether reconstituted AMs were still immunocompetent, the recovered AMs were assayed for their ability to phagocytose fluorescein-labeled zymosan-coated beads. After incubation with the beads, samples were assayed using a fluorescent-activated cell sorter to identify DiI-labeled reconstituted AMs, unlabeled resident AMs, and the proportion of these two groups undergoing phagocytosis. DiI-labeled AMs accounted for approximately 50% of all returned AMs. Additionally, the reconstituted AMs from normal BALB/c mice retained phagocytic activity compared with AMs from immunodeficient SCID mice. Reconstituted AMs demonstrated enhanced phagocytic activity compared with resident SCID AMs for up to 28 days following reconstitution. These results indicate that immunocompetent AMs can be successfully reconstituted into an immunodeficient host to partially restore alveolar host defense.