Figure 2.

GRP blockade reduces peak numbers of PNECs at 6 weeks after radiation. A: Sham plus PBS controls have rare GRP⁺ cells (black arrow) most often at branch points in the airways (GRP immunostaining). B: Six weeks after radiation, there are numerous GRP⁺ cells in distal bronchiolar epithelium (many indicated by arrows). Most GRP⁺ cells are also PGP9.5⁺ (D–F), consistent with a neuroendocrine phenotype (GRP immunostaining). Many of these cells in irradiated mice given PBS are also CC10⁺ (unpublished data), consistent with a multipotent epithelial phenotype emerging after radiation. C: Mice exposed to radiation and then injected with 77427 twice a week have fewer GRP⁺ cells in bronchiolar epithelium at 6 weeks (GRP immunostaining). D: Sham plus PBS controls have rare PGP9.5⁺ cells (none in this field) despite strong positive control staining for PGP9.5 in nerve fibers (white arrows in right lower corner) (PGP9.5 immunostaining). E: Six weeks after radiation, there are numerous PGP9.5⁺ cells in distal bronchiolar epithelium (arrows) (PGP9.5 immunostaining). PGP9.5⁺ cells are also positive for GRP (A–C) and CC10 (not shown), consistent with a multipotent epithelial phenotype after radiation. F: Mice exposed to radiation then injected with 77427 twice a week have fewer PGP9.5⁺ cells in bronchiolar epithelium at 6 weeks (PGP9.5 immunostaining). G: Quantitative image analysis shows a large increase in GRP⁺ and PGP9.5⁺ cells in lungs of mice exposed 6 weeks earlier to radiation, which is significantly decreased by treatment with 77427. Compared with sham controls, ^∗P < 0.001 and ^‡P < 0.01 for either ^#GRP⁺ foci per cm² or ^#PGP9.5⁺ cells/cm² in radiation-treated lung tissue area. Compared with radiation-treated mice; ^†P < 0.01 for either ^§P < 0.04 (PGP9.5) for mice exposed to radiation, then further injected with 77427 twice a week. Scale bars: 25 μm (A–F). L, airway lumen; V, blood vessel.