pneumocyte
pneumo.site · being built
| What it is | An epithelial cell lining the lung's alveoli, the air sacs where gas is exchanged. |
|---|---|
| Comes from | Lung progenitor |
| About | Cells lining the terminal airways that are on the way to becoming type II pneumocytes already make surfactant protein A message at 19 to 20 weeks of gestation, and mature type II cells hold it only after birth. |
| Source | Khoor A, Gray ME, Hull WM, Whitsett JA, Stahlman MT. Developmental expression of SP-A and SP-A mRNA in the proximal and distal respiratory epithelium in the human fetus and newborn. J Histochem Cytochem. 1993;41(9):1311-9. PMID: 8354874 |
| Status | being built; its twin, knowledge and helper come with pneumo.site |
Where it lives
| Lung alveolus, the air sac wall, beside squamous type 1 cells and the capillaries | mouse · PMID 24499815 |
| About 480 million alveoli in an adult human lung; a single alveolus is about 4.2 million um3 | human · PMID 14512270 |
What it does
| Type 2 cells make and secrete surfactant, which lowers the surface tension of the air sac | mouse · PMID 24499815 |
| Type 2 cells are the alveolar stem cells: they self-renew over about a year and give rise to type 1 cells | mouse · PMID 23921127 |
| After type 1 cell injury, type 2 cells expand clonally to repair the alveolus | mouse · PMID 24499815 |
What goes wrong
| Oncogenic KRAS in type 2 cells drives clonal adenomas: the stem cell programme hijacked in lung cancer | mouse · PMID 24499815 |
| Loss of many type 2 cells forces the survivors into rapid clonal expansion | mouse · PMID 23921127 |
Pictures 3
(D) Representative transmission electron microscopy (TEM) images of monocystic alveolosphere. Microvilli (MVs) observed in spheres at the apical lumen. Mitochondria (MT) displayed with blue arrow heads. A monocystic organoid from fibrotic origin displays accumulations of numerous lamellar bodies on ultrastructural level (LB, black). Black window shows intracellular LBs, while yellow and green window display extracellular LBs. High magnification images in TEM show single AT-II cell from a monocystic organoid. NC (white), MV (red arrow heads), MT (blue arrow heads) and LB (black). Scale bar = 5 µm. (E) Details of a single AT-II cell within a monocystic alveolosphere. Scale bar = 5 µm. Presence of NC, MTs, LBs and MVs. (human (primary AT-II alveolar type II cells from lung organoids); Fig. 5, panels D-E (TEM of primary human AT-II alveolosphere; rows 540-1115 of figure).)
Schröder, Rückoldt, Schubert et al 2026, Respiratory Research · CC BY 4.0
Representative immunofluorescence labeling of AT2 marker pro-SPC (green), Hu-Mitochondria (red/MAB1273), Hu-LAMP3, AGER, and Hu-PDPN in transplanted P2-4 hALOs (panels B, upper) and P12-14 hALOs (panels C, lower). Micrographs shown at 20x and 40x with negative controls. Scale bars, 100 um (20x panels), 50 um (40x panels). (human (iPSC-derived alveolar organoids in mouse lung); Figure 4, panels B and C (confocal IF micrographs; schematic panel A and dot-plot panel D excluded; rows 104-571 of full figure).)
Li, Liu, Liu et al 2025, International Journal of Biological Sciences · CC BY 4.0
Histopathological analysis of lung sections of K18-hACE2 mice inoculated with PBS (A) and infected with SARS-CoV-2 (B-F). (A) A: Alveoli; AS: Alveolar sac; B: Bronchiole. Comparatively, note the difference between the alveolar architecture of non-infected and infected mice, particularly concerning the thickening of the alveolar septa in the infected group. (B) IP: Interstitial pneumonia; DS: Dead spaces; HI: Hyperinflation. (C) IC: Inflammatory cuffing; IP: Interstitial pneumonia; V: Vasculitis. (D) BS: Blood stasis; (E) BS: Blood stasis; H: Hemorrhage; (F) E: Edema. Bar: (A-E): 100 um, (F): 50 um. (mouse (K18-hACE2, PBS control and SARS-CoV-2 infected lung sections); Figure 1.)
de Almeida, da Silva, Souza et al 2026, Microorganisms · CC BY 4.0
Papers 3
- de Almeida ALT, da Silva AMV, Souza MME, Rodrigues MPMD, Coelho FS, da Rosa LC, et al. SARS-CoV-2 Effects on Respiratory and Neurological Systems: Morphological Findings and Gene Expression in K18-hACE2 Mice Model. Microorganisms. 2026;14:852. PMID: 42075250.
- Schröder LJ, Rückoldt J, Schubert S, Knudsen L, Janciauskiene SM, Werlein C, et al. Optimized culture of primary human alveolar type II cell-derived 3D organoids from fibrotic lung tissue with phenotypic and metabolic profiling. Respir Res. 2026;27:164. PMID: 41792753.
- Li L, Liu Y, Liu L, Zhao S, Feng J, Zhou J, et al. Human Pluripotent Stem Cell-Derived Alveolar Organoids for Gene-editing and Lung Adenocarcinomas Modeling. Int J Biol Sci. 2025;21:6285-6304. PMID: 41208901.