IL-4 producing CD4+ and IgE+ cells from foals and adult horses were measured by flow cytometry. PBMC were stimulated with PMA and ionocmycin. The cells were stained for intracellular IL-4 and cell surface CD4 or IgE. (A) A representative image from a horse of each age group is shown. (B) The total number of IL-4+ cells was normalized to 100% and the relative numbers of IL-4 producing CD4+ cells (%) were calculated for each horse. Medians are shown as horizontal lines within the data points of each group. *** p < 0.001; ns = not significant.