Immune response and the hypoxic complications of lower respiratory tract respiratory infections development in children. A bibliographical review

Pneumonia is one of the most common severe infectious diseases in pediatric practice. Hypoxia is common in children with pneumonia and is one of the main predictors of poor outcome. The role of the central link in the cellular response to hypoxia is played by the family of hypoxia-inducible factors (HIF). HIF-1α is the key regulator of both T- and B-lymphocyte functions. The processes of their maturation are accompanied by the formation of circular DNA fragments, TREC (T-cell Receptor Excision Circle) and KREC (Kappa-deleting Recombination Excision Circle). TREC and KREC are unable to replicate and serve as markers for naive lymphocyte production. In its turn, HIF-1α can be used as a marker for cellular hypoxia. The use of TREC and KREC in assessing the immune system in patients with various immunological and infectious pathologies has already been described. At the same time, HIF-1α has so far been little studied as yet. The purpose of this research was to analyze the scientific bibliographical data on the HIF-1α assessment as a marker for hypoxia as well as the quantitative level of TREC and KREC as markers for the adaptive immune response; to study the bibliographical sources on the effect of hypoxia on the immune response, including as part of lower respiratory tract infections. Methods used: bibliographical research in Scopus, PubMed and Google Scholar with keywords “TREC,” “KREC,” “HIF,” “hypoxia,” “pneumonia,” “immune response,” that was then followed by the search results’ systematization, analysis and synthesis. Results: the analysis of bibliographical sources had allowed the Authors to conclude that there is a possible close connection between acute hypoxia and the formation of an adequate immune response in infectious pathologies. Research in this area is still extremely scarce. At the same time, the prospects for this area determine the need for further fundamental and clinical research. Conclusion: it is of a great scientific and clinical interest to be able to non-invasively assess the degree of acute hypoxia during an ongoing infectious disease by examining urinary HIF-1α levels. Particularly promising is the assessment of the HIF-1α level not only as a regulator of tissue adaptation to acute hypoxia, but also as a modulator of the immune response. Taking into consideration the analyzed data, both TREC and KREC appear to be the optimal markers characterizing the functional state of the adaptive immune system.