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Epigenetic Differences of Cows Classified with Biased Antibody and Cell Mediated Immune Response Traits
The identification of cattle that are better able to respond immunologically to pathogens would be useful to reduce the incidence of disease on commercial dairy farms. High Immune Response™ (HIR) technology provides a unique tool to rank animals based on their ability to respond to test antigens, and high ranking dairy cows have been shown to have a lower incidence of disease. HIR evaluates two branches of the adaptive immune response: the antibody mediated immune response (AMIR, prominent IL-4 production) which responds primarily to extracellular pathogens, and the cell mediated immune response (CMIR, prominent IFN-g production), which responds primarily to intracellular pathogens. Genetic control of the immune response has been well studied in past years, but epigenetic influences on phenotype remain to be defined. Epigenetics is defined as modifications to DNA which control gene expression without changing the DNA sequence. Specifically, DNA methylation, an epigenetic modification, is associated with a decrease in gene transcription, while the lack of DNA methylation is associated with increased gene expression. CD4+ helper T cells are mediators of AMIR and CMIR, producing cytokines, such as IL-4 and IFN-γ, for the direction of an appropriate response. Biased immune responder cattle respond strongly with either high AMIR (H-AMIR) or high CMIR (H-CMIR) to test antigens. Cows with H-AMIR/L-CMIR (H-AMIR; n=10) and H-CMIR/L-AMIR (H-CMIR; n=11) phenotypes were used to investigate mechanisms of immune response variation and the role of epigenetics in cattle immune response traits. Isolated CD4+ helper T cells from H-CMIR and H-AMIR cows were stimulated with a T-cell mitogen (ConA) and cell culture supernatants were harvested at 24 hours to quantify IL-4 and IFNγ by ELISA. DNA was extracted from unstimulated and stimulated cells and bisulfite pyrosequencing was used to quantify DNA methylation for both IL-4 and IFNγ promoters. CD4+ T cells from H-CMIR cows produced more IFN-γ (p=0.059), and significantly more IL-4 (p=0.02) than T cells from H-AMIR cows, when sampled 21 days into lactation. In H-CMIR cows higher secretion of IFN-γ was associated with decreased methylation in the promoter region of the IFNγ gene compared to H-AMIR cows (p=0.01). In contrast, there was no difference in DNA methylation at the IL-4 promoter observed between the two immune response phenotypes. This study is the first to show an association between DNA methylation and specific phenotypes.
Keywords:
Immune Response, Epigenetics, Dairy Cows