Fig. 1: In addition to AT2 cells, MHC-II is highly expressed by SPC^lowMHC^high LECs.

a Genetic construct of SPC-GFP mice and gating strategy to identify major LECs including club (yellow), multiciliated (red), alveolar type 1 (AT1, purple), SPC^low (blue), alveolar type (AT2, green) lung epithelial cells in SPC-GFP mice. b Contour plot and quantification of LEC MHC-II. CD45⁺CD24⁺MHC-II⁺ APCs depicted in dark blue. One-Way ANOVA with Holm-Sidak’ multiple comparison test. c Histogram and quantification of LEC cell sizes, One-Way ANOVA with Holm-Sidak’s multiple comparison test. Histogram and quantification for d airway epithelial marker β4 integrin and e stem cell antigen, Sca-1 by SPC-GFP^low and AT2 cells, two-tailed Mann–Whitney test. f mRNA levels of select lineage-defining transcripts in sorted LECs, two-tailed Mann–Whitney test. Sorting strategy is the same as gating strategy in Fig. 1a. g Contour plot for identification of distinct LECs in bronchioalveolar stem cell (BASC) reporter mice and quantification of LEC MHC-II, One-Way ANOVA with Tukey’s multiple comparison test. Major LECs including club (yellow), BASC (magenta), SPC^low (blue), alveolar type (AT2, green), and other cell (gray) are indicated. h Representative immunofluorescent micrograph showing anatomical location of SPC-YFP⁺ cells (green) and SCGB1A1-mCherry⁺ (red) with DAPI (blue) used as counterstain. Data is representative of n = 2 mice, 2 experiments. i Representative transmission electron micrographs for LECs sorted and pooled from n = 3 SPC-GFP mice. Experiment was repeated twice. Yellow asterisks indicate electron-dense secretory vesicles and green asterisks depict lamellar bodies. All data have n ≥ 5 mice, two independent experiments. All data are presented as mean ± SEM.