The relationship between immune fitness and saliva biomarkers of systemic inflammation.

Purpose: It is vital that Immune fitness, i.e., how well the immune system functions and reacts to challenges, can be reliably be examined. The current study aimed to compare immune fitness with assessments of saliva biomarkers of systemic inflammation. Methods: N = 108 healthy young adults (18-30-year-old students of Utrecht University, the Netherlands) participated in the study. A saliva sample was collected for biomarker assessment (Interleukin (IL)-1ß, IL-6, IL-8, IL-10, immunoglobulin A (IgA), and tumor necrosis factor-alpha (TNF-α), and c-reactive protein (CRP). Additionally, a survey was completed to assess immune fitness, mood, mental resilience, and quality of life. The correlations between the biomarker assessments, immune fitness and mood were determined. Results: No significant correlations between immune fitness and biomarkers of systemic inflammation were found. Significant sex differences in correlations with immune fitness were demonstrated for loneliness (significant only in men) and fatigue (significant only in women). For both sexes, immune fitness correlated significantly with anxiety, mental resilience, and quality of life. Conclusion: No significant correlations were found between immune fitness and saliva biomarkers of systemic inflammation. Immune fitness correlated significantly with anxiety, mental resilience, and quality of life. Sex differences were demonstrated in the relation of immune fitness with loneliness and fatigue. Future research should further investigate factors that may influence the relationship between immune fitness, mood, and biomarkers of systemic inflammation, including underlying psychological mechanisms of possible sex differences.

Test-retest reliability of single-item assessments of immune fitness, mood, and quality of life.

The use of single-item assessments is increasingly important and popular, as these enable quick real-time assessments in clinical practice or research. In this study we investigated the test-retest reliability of single-item assessments of mood ("stress", "anxiety", "depression", "fatigue", "loneliness", "being active", "optimism", and "happiness"), quality of life, and immune fitness in N = 108 participants. The analysis revealed high test-retest correlations between the single-item assessments (r = 0.67 to 0.90), moderate to excellent intraclass correlations (r = 0.672 to 0.889), and the Bland-Altman analysis revealed agreement between all test-retest assessments, except for depression. Taken together, it can be concluded that the single-item assessments of mood, quality and immune fitness have a good test-retest reliability. This strengthens the rationale for using these single item assessments.