Here, we provide the first investigation of the patterns and drivers of age-related changes in IFNγ production in a natural population, using a unique longitudinal dataset of repeated ex vivo assessments of IFNγ production in response to immune stimulation for 295 wild badgers of known age, sex and bovine tuberculosis (bTB) infection status (960 measures over a 4-year period). The gene discussed is IFNG; the disease is infection.