Total percentages of (A) IFN-γ, (B) IL-10 and (C) IL-4 producing lymphocytes in neonates (n = 18), foals until 12 weeks of age (n = 15) and in adult horses (n = 15). PBMC were stimulated with PMA and ionomycin. The cells were stained for intracellular cytokine production and were analyzed by flow cytometry. The percentages include all cells producing the respective cytokine including double positive cells. The horizontal lines within the data sets represent medians. *** p < 0.001; ** p = 0.001 to < 0.01; * p = 0.01 to 0.05; ns = not significant.