Morphofunctional Features of the Immune System Response to Sublethal Hypoxic Load in Hypoxia-Tolerant and...

Background/Objectives: The most commonly used method for determining tolerance to oxygen deficiency is applying a sublethal hypoxic load (SHL) in a decompression chamber at an altitude of 11,500 m. The aim of this study was to identify the morphofunctional characteristics of the immune system's response to SHL in animals with different tolerances to oxygen deficiency. Methods: This study was conducted on male Wistar rats. Resistance to SHL was determined at a critical altitude (11,500 m) once in a decompression chamber. To study the features of the reaction to SHL, morphological and morphometric methods, flow cytometry, and real-time PCR were used. Results: One month after SHL, rats susceptible to hypoxia, in comparison with tolerant ones, demonstrated higher numbers of cytotoxic T-lymphocytes and NK cells in the peripheral blood, thymic bodies in the cyst-like cavities formed in the thymus, and wide germinal centers of lymphoid nodules in the spleen. At the same time, rats tolerant to hypoxia demonstrated higher numbers of B-lymphocytes in the peripheral blood and a narrow marginal zone of lymphoid nodules in the spleen. In addition, animals susceptible to hypoxia demonstrated higher expression levels of proinflammatory cytokines Il1b and Tnfa in peripheral blood leukocytes in comparison with tolerant animals. Conclusions: This indicates that the immune systems of tolerant and susceptible animals respond differently to oxygen deprivation during SHL, and that the manifestations of this effect persist for at least a month afterward. The obtained data should be taken into account when conducting experiments with reference to organisms' initial hypoxia tolerance.