Immunity is one of the most variable phenotypic traits in animals;
however, some individuals may show less fluctuation in immune traits,
resulting in stable patterns of immune variation over time. It is
currently unknown whether immune variation has consequences for infectious
disease risk. In this study, we identified moderately stable immune traits
in wild African buffalo and asked whether the stability of these traits
affected bovine tuberculosis (TB) infection risk. We found that adaptive
immune traits such as the level of IFN-γ released after white blood cell
stimulation, the number of circulating lymphocytes, and the level of
antibodies against bovine adenovirus-3 were moderately repeatable (i.e.
stable) over time, whereas parameters related to innate immunity either
had low repeatability (circulating eosinophil numbers) or were not
repeatable (e.g. neutrophil numbers, plasma bacteria killing capacity).
Intriguingly, individuals with more repeatable IFN-γ and lymphocyte levels
were at a significantly higher risk of acquiring TB infection. In stark
contrast, average IFN-γ and lymphocyte levels were poor predictors of TB
risk, indicating that immune variability rather than absolute response
level better captured variation in disease susceptibility. This work
highlights the important and under-appreciated role of immune variability
as a predictor of infection risk. Seguel_2019_PRSB_data1Set of immune and physiological parameters measured over 4-years in African buffalo (Syncerus caffer)Seguel_2019_PRSB_data2Indexes of variability in immune parameters, including repeatability and coefficient of variation, in African buffalo (Syncerus caffer)