Serum TNF-Alpha and IL-10 Predict Reduced Sensitivity to Fear- and Anxiety-Related Traits in Healthy Older Dogs: Preliminary Evidence for Immune–Personality Signatures in Later Life

As dogs live longer, they face an increased risk of functional age-related changes, including physiological and behavioral alterations. However, data on these age-related processes in domestic dogs remain limited. In this study, we assessed serum concentrations of cytokines (TNF-α, IL-6, IL-10), personality and cognition using validated scales (Dog Reinforcement Sensitivity Theory Personality Questionnaire (RSTQ-D), Dog Impulsivity Assessment Scale (DIAS), and Canine Cognitive Assessment Scale (CCAS)) in 44 healthy pet dogs from two non-overlapping age groups (1-4 years old and ≥11 years old). Generalized linear models revealed small but significant (<i>p</i> = 0.001) negative effects of age-by-cytokine interactions in predicting sensitivity to RST personality traits related to fear and anxiety in older dogs. Specifically, higher TNF-α and IL-10 levels predicted lower scores on the Fight/Flight/Freeze System (FFFS) and the Behavioral Inhibition System (BIS). These findings provide novel insights into previously unrecognized associations between the immune system and personality in healthy older dogs, possibly contributing to broader profiles of vulnerability or, conversely, resilience. Further research is needed to confirm these associations and clarify their functional meaning. Such knowledge could facilitate the early identification of complex aging-related phenotypes and inform individualized preventive strategies to support the health and well-being of aging companion dogs.