(A–G) Illustration in A shows the design of the confocal imaging studies shown in B–G. As indicated in A, we microinstilled fluorescent beads (yellow) in airspaces of 3 imaging fields of at least 30 alveoli in live, perfused lungs of an AT1-CFTR^null-GFP mouse, then generated images over 2.5 hours to define bead location, group formation, and movement. GFP fluorescence of the imaging fields was in the Medium category. Images in B show the initial locations and size distributions of example bead groups that formed within 0.5 hours of beads microinstillation. Dashed squares show locations of the high-power views shown in i and ii. The arrowhead shows a small cluster of beads located adjacent to a GFP-expressing (cyan) flat alveolar septum, while the arrow points out a microaggregate located at a TdTomato-expressing (magenta) alveolar niche. mv, microvessel; air, airspace. Images and group data in C–G show spontaneous movement of all bead groups (C–E) or small clusters (F and G) in the 3 imaging fields over the first 3 hours after beads microinstillation. Bead groups were categorized according to whether the adjacent AT1 cell expressed WT CFTR (signaled by TdTomato fluorescence) or CFTR^null (signaled by GFP fluorescence), as indicated. Note in the images in C and F, beads located adjacent to WT CFTR-expressing AT1 cells moved (C and i in F), but beads adjacent to CFTR^null-expressing AT1 cells did not (ii in F). In D and G, circles indicate n and each represent 1 bead group. Data are shown as mean ± SEM; *P < 0.05 by 2-tailed t test. In E, stacked bars represent bead groups as proportions of the total number; *P < 0.05 by χ² test. Scale bars: 30 (B), 3 (i and ii in B and C), and 15 (F) μm.