Human presence and work in Antarctica occur under challenging climatic, psychophysiological, and social conditions. The health of expedition participants is a critical factor, and a pre-expedition medical assessment is extremely important. The immune system plays a crucial role in maintaining satisfactory health and in the successful adaptation to adverse living conditions. In the current study, we evaluated the prognostic significance of previously identified accentuations on the health status of participants and their adaptation to Antarctic conditions. Immunophenotyping was performed on 43 male Ukrainian antarctic expedition (UAE) members before the expedition and after their return, assessing the dynamics of laboratory indicators and conducting a detailed analysis of their health status throughout the entire expedition. According to the results, UAE participants with favorable and unfavorable adaptation showed differences in immunophenotypic indicators. The majority of UAE participants with favorable adaptation had T-helper (CD3 + CD4+) levels (> 35%), balanced (< 24%) expression of HLA-DR on cytotoxic T-lymphocytes (CD4 + CD8+), and proportions and absolute levels of NK-lymphocytes (5–18% and 100–400). In contrast, UAE participants with unfavorable adaptation exhibited balanced levels significantly less frequently. NK cell levels within the reference (favorable) range (5–18%) were virtually absent in UAE participants with unfavorable adaptation (1/12), whereas they were typical in participants with favorable adaptation. The combination of two diagnostically significant immune parameters yields higher accuracy. Increased expression of HLA-DR on cytotoxic T-lymphocytes and elevated NK-lymphocyte content significantly enhance the prognostic value of the diagnostic algorithm. Thus, in the group of participants with favorable adaptation, only 9 (30%) had one of these accentuations, while in the group with unfavorable adaptation, all 12 participants had one of these accentuations (P < 0.0001, OR = 59.211). In all Antarctic expedition participants, cortisol levels significantly increased in the first quarter compared to baseline values, followed by dynamic fluctuations throughout the expedition. Cortisol levels returned to baseline after the expedition. The results demonstrate that staying in Antarctica requires adaptive processes that are directly dependent on the balanced function of the immune system. Chronic stress, in conjunction with immune accentuations, complicates successful adaptation. Further investigation into immune processes and adaptation characteristics will allow for the prediction of the risk of adverse adaptation processes, improve participant selection, and facilitate the implementation of proactive measures to prevent the deterioration of the health status of polar expedition members.
