The role of genetically determined hypoxia resistance in warm-blooded animals related to the neutrophil effector functions in experimental adjuvant-induced rheumatoid arthritis

Hypoxia can be both a cause and a consequence of pathogenic events in the infectious, autoinflammatory, and autoimmune processes. Given that human and animal populations are genetically heterogeneous in terms of whole-body resistance to oxygen deficiency, the modern approach to predicting and treating diseases associated with impaired immune regulation requires taking into account the role of hypoxia among pathogenetic mechanisms of inflammation. The purpose of the study was to evaluate the features of neutrophil effector functions under normal conditions and in presence of an induced inflammatory process in animals with genetically predetermined high and low resistance to hypoxia. For our studies, we used 8-monthold male rats of two breedings with different genetic tolerance to hypoxia (highly resistant HR/SmY line; and low-resistant LR/SmY line), weighing 400-450 g. Rats from the experimental groups of the HR/SmY and LR/SmY lines were induced to develop immune responses in a model of rheumatoid arthritis (RA). After 35 days, the blood samples from the animals were incubated with Indian ink suspension (1:10). The smears fixed in formalin vapor were stained with 0.5% methylene blue solution and analyzed with light microscopy (400×). Phagocytic index (PHI), phagocytic number (PN), and the number of suicidal netosis with partial and complete chromatin decondensation were calculated. The significance of differences in the groups was assessed by the Mann–Whitney test and the Student’s t-test. PHI and PN of neutrophils did not significantly differ between control groups of LR/SmY and HR/SmY animals (52.5%/49%; 1.68/1.80, respectively). In experimental groups, the PHI of neutrophils of LR/SmY line (66%, p ≤ 0.05) exceeded that of the HR/SmY line (56%). With systemic inflammation model, the PHI of neutrophils in the group of low-tolerance rats increased by 1.26 (p ≤ 0.05) times, and the number of neutrophils capturing 2-8 particles increased by 1.3 (p  0.01) times in healthy rats. In experimental HR/SmY group, 1.81% of more active neutrophils absorbing 9 to 12 particles (p ≤ 0.01) were recorded, with PHI was 1.2 times lower than that of the LR/SmY line. In healthy HR/SmY rats, higher ratio of neutrophils (1.4-fold increase) was involved in the process of suicidal netosis than in similar group of the LR/SmY line (p ≤ 0.05). Systemic inflammation in the LR/SmY group caused a twofold increase in NETs (19.67%), which was 1.7 times higher than in the experimental HR/SmY group. The organisms with genetically determined low resistance to hypoxia, when accompanied by inflammatory process, show higher burden on cell immunity in the course of phlogogen elimination as compared to highly resistant ones, which may predispose them for more severe pathogenic forms of inflammatory and autoimmune diseases.