IFN-γ responses to no stimulation (A) and PWM stimulation (B) by M. bovis-infected (n = 13) (open squares) and noninfected (n = 4) (solid squares) reindeer. Heparinized blood samples were obtained at various time points (months, starting with December, indicated on x axis) and dispensed immediately in 1.5-ml aliquots into individual wells of a 24-well plate. Treatment was no stimulation (PBS) or PWM (20 μg/ml). Blood cultures were incubated for 48 h, plasma was harvested, and IFN-γ concentrations were determined using an ELISA-based kit (Cervigam; Pfizer Animal Health). Absorbencies of standards and test samples were read at 450 nm using an ELISA plate reader. Duplicate samples for individual treatments were analyzed. Data are presented as mean OD readings ± standard errors of the means. Responses to either no stimulation (A) or PWM stimulation (B) did not differ (P > 0.05) between infected and noninfected reindeer. Due to disparate responses to no stimulation versus PWM, the scales for the two graphs are different.