Maternal T-lymphocytes in equine colostrum express a primarily inflammatory phenotype

The purpose of this study was to characterize maternal immune cells in colostrum of mares. Cell phenotypes and cytokine secretion from mare peripheral blood mononuclear cells (PBMC) and cells from colostrum were analyzed by flow cytometry and by multiplex cytokine analysis. Equine colostral leukocytes were composed of mainly CD8+ and CD4+ lymphocytes. CD8+ cells were significantly enriched in colostrum compared to PBMC (n = 35). Colostral T-cells (n = 13) responded to stimulation with PMA/ionomycin with a significantly higher magnitude of IL-17 (p = 0.037) and similar IFN-γ concentrations (p = 0.305), while IL-4 (p = 0.0002) and IL-10 (p = 0.0002) production was decreased compared to PBMC. CD4+ and CD8+ T-cells in colostrum produced IFN-γ (n = 4). The findings show that colostrum T-cells can produce all four cytokines investigated here but most cells are polarized toward IL-17 and IFN-γ production and an inflammatory phenotype. Maternal T-cells likely migrate to the colostrum in a selective manner and may have specific roles in neonatal immune development.