Cytokines Gene Expression Patterns of Bovine Milk During Middle and Late Stages of Lactation

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Abstract
The cytokine mRNA profiles of the bovine mammary gland were investigated using newly developed TaqMan®real‐time polymerase chain reaction systems (Applied Biosystems, Foster City, CA, USA). Transcriptional activity of six cytokines, interleukin (IL)‐2, IL‐6, IL‐12, interferon (IFN)‐γ, tumour necrosis factor (TNF)‐α and granulocyte‐macrophage colony stimulating factor (GM‐CSF) was studied during the mid‐ and late‐lactation stages. Transcripts for TNF‐α, GM‐CSF, and IFN‐γ were detected in all samples of both stages. However, IL‐12 was only detected in 80 and 58 % of late‐ and mid‐lactation samples, respectively. IL‐12 expression was up‐regulated in late lactation in comparison with the corresponding level in mid‐lactation. The cytokines interaction in late lactation was more co‐ordinated and their transcriptional levels were significantly correlated among each other, whereas, in mid‐lactation significant correlation of the cytokines transcription was only seen with the TNF‐α, GM‐CSF, and IFN‐γ. Cytokine mRNA profiles between mid‐ and late lactation showed significant differences, which can be attributed to the dramatic changes that the mammary gland is subjected to during late lactation. The significant elevation of IL‐12 transcriptional activity in late lactation and its relevance to the mammary gland immunity is discussed.