Expression of cathelicidins mRNA in the goat mammary gland and effect of the intramammary infusion of lipopolysaccharide on milk cathelicidin-2 concentration

Cathelicidins are a family of antimicrobial peptides found in neutrophils and the epithelium that have broad-spectrum activity against bacteria. This study aimed to investigative the mRNA expression of cathelicidins and protein localization of cathelicidin-2 in the goat mammary gland and its secretion into milk. The mRNA expression of cathelicidins was examined in different regions of the mammary gland by reverse transcription PCR. A cathelicidin-2 antibody was raised in rabbits by immunization with a synthetic cathelicidin-2 peptide consisting of 17 amino acids. The protein localization of cathelicidin-2 was investigated in the mammary gland by immunohistochemistry. Skim milk was collected before (0 h) and 2, 4, 8, 12, and 24 h after the intramammary infusion of lipopolysaccharide and saline, and the concentration of cathelicidin-2 was examined by an enzyme immunoassay. The mRNAs of cathelicidin-1, 2, 3, 6, and 7 were expressed in both the teat and deep region of the mammary gland from healthy and mastitic goats. Immunoreactive cathelicidin-2 was not localized in the epithelial cells of the teat skin, teat cistern, or mammary alveoli, whereas it was localized in polymorphonuclear cells in the mammary gland and those collected from the blood and milk. Cathelicidin-2 was detected in skim milk by Western blotting. The concentration of cathelicidin-2 in milk increased 4 h after the intramammary infusion of lipopolysaccharide. These results suggest that cathelicidin-2 is expressed in polymorphonuclear cells and is secreted into milk in goat.