Nitric oxide responses of monocyte-derived macrophages cultured from MAP-exposed cattle, subgrouped into low and high IFN-γ responders. PBMC were isolated from the whole blood from MAP-exposed (n = 10) cattle and monocytes isolated by CD14⁺ selection using MACS^®. The MAP-exposed cattle were subgrouped into low (n = 5) or high IFN-γ responders (n = 5), based on responses in the whole-blood MAP-specific IFN-γ assay. Cultured bovine macrophages were incubated with LPS (25 ng/mL), MAP 316v antigen (316v Ag) or M. bovis antigen (PPDB) (100 μg/mL), live MAP or M. smegmatis strains at an MOI of 1:1 (viable count) for a period of 48 h, without pre-treatment or after IFN-γ pre-treatment for 1 h. Data are the mean plus standard error of the mean of three replicate cultures from one out of two independent experiments. Hash denotes a significant increase (P ≤ 0.05) in nitric oxide response to incubation with live MAP in the high compared to the low IFN-γ responder subgroup, with or without IFN-γ pre-treatment.