Ratios of (A) IFN-γ⁺/IL-4⁺ and (B) IFN-γ⁺/IL-10⁺ lymphocytes in foals up to 3 months of age and adult horses. PBMC were stimulated with PMA and ionomycin. The cells were stained for intracellular cytokine production and measured by flow cytometry. The total percentages of IFN-γ, IL-4 and IL-10 producing lymphocytes were determined and ratios were calculated for the respective cytokines. The horizontal lines within the data points show the medians. *** p < 0.001; * p = 0.01 to 0.05.