MORPHO-FUNCTIONAL CHANGES OF THYMUS AND CONTENTS OF BLOOD LYMPHOCYTE SUBPOPULATIONS IN FEMALE WISTAR RATS WITH DIFFERENT RESISTANCE TO HYPOXIA IN SYSTEMIC INFLAMMATORY RESPONSE
Authors: Kosyreva A. M. , Dzhalilova D. Sh. , Makarova O. V. , Sladkopevtsev A. S. 
Published: October 2019

Hypoxia and immune reactions are closely interrelated at molecular, cellular and organism levels, and the individuals differ in resistance to oxygen deficiency. Animals with high and low resistance to hypoxia have different adaptive capabilities and predisposition to the development of inflammatory diseases. Data on the individual characteristics of hypoxia resistance in female laboratory animals and humans, and its relationship to immune system reactions in both normal conditions and inflammatory diseases are not available in the literature. It is known, however, that acute infectious and inflammatory diseases develop at lesser rates and are less severe in women and female laboratory animals than in males, which can be explained by higher resistance of females to hypoxia. The aim of our study is to reveal the features of morpho-functional thymus changes, and subpopulation of peripheral blood lymphocytes in systemic inflammatory response induced by LPS administration to female Wistar rats with different resistance to hypoxia. 

Resistance of mature female Wistar rats to hypoxia was determined as a survival period in a ventilated lowpressure chamber simulating high altitude condition (11 500 m). The rats with a lifetime “at high altitude” of > 180 s have been classified as highly resistant to hypoxia, and the animals surviving for < 20 seconds were designated low-resistant. One month after determining the hypoxia resistance, the females were injected intraperitoneally with E. coli O26:B6 lipopolysaccharide (LPS) at a dose of 1.5 mg/kg during the dioestrus phase. The animals were withdrawn from the experiment by i/m Zoletyl injection (15 mg/kg) one day after LPS administration. The relative volume fractions of thymic cortex and medulla were evaluated; the areas of necrosis were determined in the liver, and the number of neutrophils in the interalveolar septa was counted in the lungs. The serum contents of corticosterone, testosterone, TGF-β were determined. A flow cytometry evaluation of the relative and absolute numbers was performed for major subpopulations of lymphocytes in peripheral blood. The number of apoptotically dying cells of the thymus was assessed. For statistical processing of the obtained data, the Statistica 8.0 software was applied, using criteria of multiple comparisons by Kruskal–Wallis and Dann. The differences were considered statistically significant at p < 0.05.

In both high- and low-resistant to hypoxia females, the development of a systemic inflammatory -response was accompanied by a moderately severe thymic involution, apoptosis of thymocytes, an increase in the absolute number of NK, and rise of testosterone and corticosterone contents. LPS injection into low-resistant rats, if compared to females highly resistant to hypoxia, led to more severe manifestations of systemic inflammation, i.e., a pronounced inflammatory reaction in the lungs and a more extensive liver necrotic area accompanied by increased absolute numbers of regulatory T lymphocytes and T helper cells, and more pronounced thymic accidental involution with apoptotic death of thymocytes. Systemic manifestations of inflammation were less pronounced in hypoxia-resistant female rats, which was apparently associated with activation of lymphocyte  migration from the thymus and blood to the inflammation focus, and development of more effective immune response.

Conclusion: immune reactions in the systemic inflammatory response induced by LPS in female Wistar rats depend on individual resistance to hypoxia. These data should be used to develop approaches to personalized therapy of infectious and inflammatory diseases in women.