Increased milk levels of transforming growth factor-alpha, beta1, and beta2 during Escherichia coli-induced mastitis

Among the gram-negative bacteria that cause mastitis, Escherichia coli are the most prevalent. The innate immune system provides initial protection against E. coli infection by detecting the presence of the foreign pathogens and by mounting an inflammatory response, the latter of which is mediated by cytokines such as IL-1beta, IL-8, and tumor necrosis factor (TNF)-alpha. Although changes in these cytokines during mastitis have been well-described, it is believed that other mediators moderate mammary gland inflammatory responses as well. The growth factors/cytokines transforming growth factor (TGF)-alpha, TGF-beta1, and TGF-beta2 are all expressed in the mammary gland and have been implicated in regulating mammary gland development. In other tissues, these growth factors/cytokines have been shown to moderate inflammation. The objective of the current study was to determine whether TGF-alpha, TGF-beta1, and TGF-beta2 milk concentrations were altered during the course of E. coli-induced mastitis. The contralateral quarters of 11 midlactating Holstein cows were challenged with either saline or 72 cfu of E. coli, and milk samples were collected. Basal milk levels of TGF-alpha, TGF-beta1, and TGF-beta2 were 98.81 +/- 22.69 pg/mL, 3.35 +/- 0.49 ng/mL, and 22.36 +/- 3.78 ng/mL, respectively. Analysis of whey samples derived from E. coli-infected quarters revealed an increase in milk levels of TGF-alpha within 16 h of challenge, and these increases persisted for an additional 56 h. Elevated TGF-beta1 and TGF-beta2 milk concentrations were detected in E. coli-infected quarters 32 h after challenge, and these elevations were sustained throughout the study. Because TGF-alpha, TGF-beta1, and TGF-beta2 have been implicated in mediating inflammatory processes, their induction during mastitis is consistent with a role for these molecules in mediating mammary gland host innate immune responses to infection.