CD25 expression by bovine CD2− NK cells was significantly increased following co-culture with autologous BCG-infected DCs. Monocyte-derived DCs were cultured for 3 days and infected with BCG (MOI 5) for 24 h. Autologous NKp46+ cells were enriched from peripheral blood and cultured with BCG-infected DCs at a ratio of 5 NK cells per DC. NK cells cultured with media, BCG, uninfected DCs or with recombinant bovine IL-12 and recombinant human IL-18 served as controls. After 18 h of co-culture, cells were labelled with mAbs for NKp46, CD2 and CD25 and analysed by flow cytometry. FACS plots from one representative animal illustrate the expression of CD25 by NKp46+ NK cells after culture with media, BCG, uninfected DCs, BCG-infected DCs or with IL-12 and IL-18 (A). Positive cells were identified based on FMO controls. Pooled data from five calves illustrate the average MFI ± SD of CD25 expression by NK cells (B). Pooled data from five calves displays the average percentage of CD25+ NK cells ± SD (C). Pooled data from five calves indicate the average MFI ± SD of CD25 expression by CD2+ (lighter bars) and CD2− (darker bars) NK cells (D). Data were normally distributed (p > 0.05) and significance between co-culture conditions was assessed using 2-sample t tests. p < 0.05*, p < 0.01**.