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.