Differential gene expression of cytokine and cell surface molecules in T cell subpopulation derived from mammary gland secretion of cows

Problem: As T cell subpopulations in the mammary gland secretion (MGS) of cows dynamically vary through the lactation cycle, their functional analysis is important to understand the mammary immune responses. Method of study: T cell subpopulations were positively selected from MGS during lactation period and non-lactation period (dry period) by a magnetic cell sorter. The messenger RNA (mRNA) expression of cytokine and cell surface molecules in the subpopulations stimulated with anti-CD3 was investigated using reverse transcription-polymerase chain reaction (RT-PCR). Results: CD4⁺ T cells from MGS significantly expressed mRNA of interferon (IFN)-γ, interleukin (IL)-2, granulocyte-macrophage colony-stimulating factor (GM-CSF), transforming growth factor (TGF)-β, tumor necrosis factor (TNF)-α, IL-4, CD40 ligand (CD40L), Fas ligand (FasL) and IL-2 receptor (IL-2R) during dry period, and mRNA of IFN-γ, IL-2 and TGF-β during lactation period. Their expression during lactation period was always less than that during dry period. CD8⁺ T cells from MGS substantially expressed mRNA of IFN-γ, IL-2, GM-CSF, TGF-β, TNF-α, FasL and IL-2R during dry period and mRNA of IFN-γ, GM-CSF, TGF-β, TNF-α and c-kit during lactation period. The TGF-β, TNF-α, c-kit and IL-2R mRNA expression of T cells in MGS during lactation period mostly depended on γδ T cells. Interestingly, c-kit mRNA was exclusively expressed in γδ T cells. Conclusions: The cytokine expression of T cells in MGS of cows depended on the T cell subpopulations. The present findings suggested that the activation of γδ T cells via c-kit receptor participated in the suppressed expression of cytokine mRNA in T cells during lactation period.