Effect of age and mitogen on the frequency of interleukin-4 and interferon gamma secreting cells in foals and adult horses as assessed by an equine-specific ELISPOT assay

Peripheral blood mononuclear cells (PBMCs) were obtained from 6 foals <1 week of age, 6 foals between 3 and 4 months of age, and 10 adult horses. PBMCs were stimulated with concanavalin A (ConA) or calcium ionomycin–phorbol myristate acetate (CaI–PMA) and the frequency of interferon IFN-γ and IL-4 secreting cells was measured using an equine-specific ELISPOT assay. The number of IFN-γ secreting cells was significantly lower in both groups of foals than in adult horses regardless of the mitogen used for stimulation. The number of IFN-γ secreting cells was significantly higher in cells stimulated with CaI–PMA than in cells stimulated with ConA. In cells stimulated with CaI–PMA, the number of IL-4 secreting cells was significantly lower in both groups of foals compared to adult horses. In adult horses only, CaI–PMA stimulation resulted in significantly more IL-4 secreting cells than ConA stimulation. Regardless of age, the ratio of IFN-γ/IL-4 spot forming cells (SFC) was significantly higher in cells stimulated with CaI–PMA than in cells stimulated with ConA. These findings indicate that the frequency of IFN-γ and IL-4 secreting cells is lower in foals than in adult horses and that the type of mitogen used has a profound effect on the relative production of both cytokines.