The effects of pessimism on cell-mediated immunity in rats.

We used a recently developed ambiguous-cue interpretation (ACI) paradigm to investigate whether 'optimism' and 'pessimism' as behavioural traits may be interrelated with immune functions in rodents. To this aim, in a series of ACI tests (cognitive bias screening, CBS), we identified rats that displayed 'pessimistic' and 'optimistic' traits. We found significant differences in immune biomarkers between 'optimistic' and 'pessimistic' animals. Moreover 'pessimism' was associated with significantly lower relative weight of the spleen and thymus, significantly decreased proliferative activity of splenocytes. Pessimism was associated with an increased production of interleukin-(IL)1β and IL-4, activin A, l-selectin, interferon (IFN)-γ and some chemokines and receptors for advanced glycation endproducts. The findings indicate an inflammatory profile in "pessimistic" animals.