Short communication: Cellular localization of haptoglobin mRNA in the experimentally infected bovine mammary gland.

Expression of haptoglobin (Hp) mRNA, one of the major acute phase proteins in cattle, was demonstrated in homogenates of the bovine mammary gland. The aim of this study was to localize Hp mRNA expression within the udder at the cellular level during the first 24 h of infection with Escherichia coli. For this purpose, 3 quarters of 3 cows were subsequently inoculated with E. coli at 6, 12, and 24 h preslaughter; the fourth quarter received saline at 24 h preslaughter as a control. After slaughter, tissue samples of each quarter were collected for analyses by in situ hybridization and real-time reverse-transcription PCR. Haptoglobin mRNA expression was allocated to the alveolar epithelium of the mammary gland. Quantification of Hp-positive cells in in situ hybridization of Hp mRNA from tissue homogenates and of Hp protein in milk confirmed increasing concentrations within 24 h of infection.