IFN-γ secretion by neonate and calf NK cells. (A) IFN-γ response of NK cells from neonates (open bars) and calves (filled bars) to rhIL-12. Sorted NKp46⁺ cells were cultured in the presence of rbIL-2 or rhIL-15 for 7–10 days. IFN-γ concentrations in the supernatants were analysed by ELISA after stimulation for 20 h with various concentrations of rhIL-12. Data shown are means ± SEM of four individuals. (B) IFN-γ response induced in NK cells by cross-linking of their NKp46, CD2 or CD8 receptors. RbIL-2 or rhIL-15 activated NK cells were seeded in plastic wells pre-coated with NKp46, CD2 or CD8 mAbs or without antibody, then incubated for 24 h in the presence or not of rhIL-12 (100 pg/mL). The concentration of IFN-γ in the supernatants was analysed by ELISA. Data shown are means ± SEM of five individuals. Statistical analyses were carried out with the nonparametric Mann–Whitney test. * p < 0.05, ** p < 0.01 is the comparison between IFN-γ secretion in the presence or absence of antibody cross-linking.