The Effect of Lipopolysaccharide on Blood Cytokine Levels in Rats Exposed to Chronic Unpredictable Mild Stress of Different Durations

In recent years, the role of the immune system in the implementation of the stress response has been in the focus of neurobiological research. Chronic stress is often associated with cytokine imbalance and the development of a persistent inflammatory response. The aim of this study was to investigate the effect of lipopolysaccharide (LPS) on blood cytokine levels in rats exposed to chronic unpredictable mild stress (CUMS). The study was carried out on 90 male Wistar rats, were exposed to CUMS for 1–4 weeks, while being preadministered either LPS (experiment) or physiological saline (control). The serum concentrations of TNF-α, IL-4, and IL-10 were determined by ELISA. After the first week of CUMS modeling, LPS-preadministered animals showed a statistically significant increase in IL-10 and TNF-α levels, whereas CUMS exposure alone was not accompanied by changes in the studied cytokines. After two weeks of stress exposure, IL-10 and TNF-α levels were increased both in the experiment and in the control. After three weeks of negative emotiogenic loads, TNF-α level was elevated only with CUMS exposure alone. After four weeks of stress exposure, no statistically significant changes in IL-4, IL-10, and TNF-α levels were observed in any of the experimental groups compared to intact rats. Thus, LPS preadministration leads to the activation of immune responses at early stages of CUMS modeling, whereas at later stages, a prior antigenic exposure does not affect stress-induced changes in the concentration of the studied cytokines. The obtained data are promising in terms of developing new methods and approaches for the prevention or correction of immune-dependent stress-induced disorders.