The relationship between self-reported immune fitness and salivary immune biomarker concentrations

Immune fitness refers to the body's ability to respond to health challenges by activating an appropriate immune response. Perceived immune fitness can be assessed using a single-item scale ranging from 0 (very poor) to 10 (excellent). The aim of the current study (n = 29 healthy volunteers) was to evaluate the relationship between perceived immune fitness and immune biomarker concentrations in saliva. Hourly assessments of immune fitness were made throughout the day (09:30 - 15:30), and saliva samples were collected accordingly. The concentrations of interleukin (IL)-1β, IL-6, IL-8, and tumor necrosis factor-alpha (TNF-α) were determined using multiplex immunoassay. While immune fitness scores remained stable during the day, biomarker assessments showed some fluctuations. For IL-6, significant negative correlations were found between IL-6 concentration at 10:30 and immune fitness scores at 10:30 (r = -0.512), 11:30 (r = -0.383), and 12:30 (r = -0.443), and between the IL-6 concentration and immune fitness score at 15:30 (r = -0.704). For IL-8, significant correlations were found between IL-8 concentration at 10:30 and immune fitness scores at 10:30 (r = -0.480), 12:30 (r = -0.456), and 14:30 (r = -0.429). For TNF-α, significant positive correlations were found between TNF-α concentration at 13:30 and immune fitness scores at 13:30 (r = 0.517) and 14:30 (r = 0.477). No significant correlations were found between immune fitness and IL-1β. In conclusion, immune fitness scores remained stable throughout the day, and were significantly associated with salivary concentrations of IL-6, IL-8, and TNF-α at certain time points.