Metabolic and immunological functions of the lungs

The metabolic and immunological functions of the lungs are the subject of active scientific research. In recent years, methods for studying organic and inorganic volatile compounds in exhaled air and its condensate have been standardized. The metabolic function of the lung parenchyma involves the regulation of water and electrolyte balance, as well as biologically active amines and peptides. The unique properties of type 2 alveolar cells and alveolar macrophages are manifested in the synthesis and recirculation of surfactant. Pulmonary capillary endothelial cells play a special role, converting angiotensin-1 (a decapeptide) into angiotensin-2 (an octapeptide) with the help of angiotensin-converting enzyme.

The aim was to study the metabolic, immunological and endocrinological functions of the lungs, as well as the diagnostic role of exhaled air condensate.

Results. The adult lungs contain approximately 20% immune cells, which maintain normal homeostasis and participate in the implementation of a protective barrier against various pathogens and allergens. A significant role is played by mucosal immunity, which involves mucosa-associated lymphoid tissue, immune cells, secretory immunoglobulin A, and various enzymes. Clinical manifestations of immunopathological reactions of the respiratory system are diverse. Thus, allergic reactions of both immediate and delayed types can be observed in clinical practice. Granulomatous processes of the pulmonary parenchyma have a special place. Neuroepithelium in the mucous membrane of the respiratory tract plays an important role in the differentiation of cell structures and in the morphogenesis of lung tissue. However, the participation of the lungs in endocrinological reactions remains a poorly studied direction.

Conclusion. The research of metabolic, immunological and endocrinological functions of the lungs identified a number of biological markers associated with bronchial asthma, COPD, lung cancer, and pneumonia. Studies of the proteome of exhaled air condensate have brought us closer to the discovery of new biological markers.

1. Das S., Pal M. Review – non-invasive monitoring of human health by exhaled breath analysis. J. Electrochem. Soc. 2020; 167 (3): 037562. DOI: 10.1149/1945-7111/AB67A6.

2. Marshall B.E. Editorial views: non-respiratory functions of the lung. Anesthesiology. 1973; 39 (6): 573–574. DOI: 10.1097/00000542-197312000-00001.

3. Pauling L., Robinson A.B., Teranishi R., Cary P. Quantitative analysis of urine vapor and breath by gas-liquid partition chromatography. Proc. Natl. Sci. 1971; 68 (10): 2374–2376. DOI: 10.1073/pnas.68.10.2374.

4. Busewski B., Kesy M., Ligor T., Amann A. Human exhaled air analytics: biomarkers of diseases. Biomed. Chromatogr. 2007; 21 (6): 553–566. DOI: 10.1002/bmc.835.

5. Shaji J., Jadhav D. Breath biomarker for clinical diagnosis and different analysis technique. Res. J. Pharm. Biol. Chem Sci. 2010; 1 (3): 639–653. Available at: https://www.rjpbcs.com/pdf/2010_1(3)/75.pdf

6. Horváth I., Barnes P.J., Loukides S. et al. A European Respiratory Society technical standard: exhaled biomarkers in lung disease. Eur. Respir. J. 2017; 49 (4): 1600965. DOI: 10.1183/13993003.00965-2016.

7. Chan H.P., Tran V., Lewis C., Thomas P.S. Elevated levels of oxidative stress markers in exhaled breath condensate. J. Thorac. Oncol. 2009; 4 (2): 172–178. DOI: 10.1097/JTO.0b013e3181949eb9.

8. Liang Y., Yeligar S.M., Brown L.A. Exhaled breath condensate: a promising source for biomarkers of lung diseases. Sci. World J. 2012; 2012: 217518. DOI: 10.1100/2012/217518.

9. Kuroki Y., Voelker D.R. Pulmonary surfactant proteins. J. Biol. Chem. 1994; 269 (42): 25943–25946. Available at: https://www.jbc.org/article/S0021-9258(18)47138-4/fulltext

10. Whitsett J.A., Wert S.E., Weaver T.E. Alveolar surfactant homeostasis and the pathogenesis of pulmonary disease. Annu. Rev. Med. 2010; 61: 105–119. DOI: 10.1146/annurev.med.60.041807.123500.

11. Nikadi P.O., Merrit T.A., Pillers D.A. An overview of pulmonary surfactant in the neonate: genetics, metabolism and the role of surfactant in health and disease. Mol. Genet. Metabol. 2009; 97 (2): 95–101. DOI: 10.1016/j.ymgme.2009.01.015.

12. Whitsett J.A., Sthalman M.T. Impact of advances in physiology, biochemistry and molecular biology on pulmonary disease in neonates. Am. J. Respir. Crit. Care Med. 1998; 157 (4): S67–71. DOI: 10.1164/ajrccm.157.4.nhlb1-2.

13. Borie R., Danel C., Debray M.P. et al. Pulmonary alveolar proteinosis. Eur. Resp. Rev. 2011; 20 (120): 98–107. DOI: 10.1183/09059180.00001311.

14. Parajpe M., Muller-Goymann C.C. Nanoparticle-mediated pulmonary drug delivery: a review. Int. J. Mol. Sci. 2014; 15 (4): 5852–5873. DOI: 10.3390/ijms15045852.

15. Jia G., Guo T., Liu L., He C. Observational and genetic evidence reveals the effect of serum lipid levels on COPD risk. Int. J. Chron. Obstruct. Pulmon. Dis. 2025; 20: 2705–2714. DOI: 10.2147/COPD.S503030.

16. Inonu H., Doruk S.,Sahin S. et al. Oxidative stress levels in exhaled breath condensate associated with COPD and smoking. Respir. Care. 2012; 57 (3): 413–419. DOI: 10.4187/respcare.01302.

17. Khurana V., Goswami B. Angiotensin converting enzyme (ACE). Clin. Chim. Acta. 2022; 524: 113–122. DOI: 10.1016/j.cca.2021.10.029.

18. Kryukova N.O., Rakunova E.B., Kostinov M.P. et al. [Secretory immunoglobulin A of the respiratory system and COVID-19]. Pul'monologiya. 2021; 31 (6): 792–798. DOI: 10.18093/0869-0189-2021-31-6-792-798 (in Russian).

19. Gessner C., Scheibe R., Wötzel M. et al. Exhaled breath condensate cytokine patterns in chronic obstructive pulmonary disease. Respir. Med. 2005; 99 (10): 1229–1240. DOI: 10.1016/j.rmed.2005.02.041.

20. Cutz E., Yeger H., Pan J., Ito T. Pulmonary neuroendocrine cell system in health and disease. Curr. Respir. Med. Rev. 2008; 4 (3): 174–186. DOI: 10.2174/157339808785161314.

21. Dressel H., Muller F., Fisher R. et al. Independent information of nonspecific biomarkers in exhaled breath condensate. Respiration. 2010; 80 (5): 401–409. DOI: 10.1159/000319945.

22. Beg M., Alzoghaibi M., Abba A., Habib S. Exhaled nitric oxide in stable chronic obstructive pulmonary diseases. Ann. Thorac. Med. 2009; 4 (2): 65–70. DOI: 10.4103/1817-1737.44649.

23. Borrill Z.L., Roy K., Singh D. Exhaled breath condensate biomarkers in COPD. Eur. Respir. J. 2008; 32 (2): 472–486. DOI: 10.1183/09031936.00116107.

24. Ryabokon A.M., Anaev E.Kh., Kononikhin A.S. et al. [Comparative proteomic analysis of exhaled breath condensate in patients with lung carcinoma using high resolution mass-spectrometry]. Pul'monologiya. 2014; (1): 5–11. DOI: 10.18093/0869-0189-2014-0-1-5-11 (in Russian).

25.