No abstract

This study aimed to determine the production site of antimicrobial peptide S100A8 in the goat mammary gland and changes in its concentration in milk after lipopolysaccharide (LPS) challenge. Sixteen Tokara goats were used in this study for mammary gland tissue, blood leukocyte, and milk somatic cell collection and LPS challenge. The mRNA expression and protein localization of S100A8 in the mammary gland parenchyma and teat, blood leukocytes, and milk somatic cells were examined by reverse-transcription PCR and immunohistochemistry. The S100A8 concentration in milk was measured at 0 to 144 h after intramammary challenge of LPS by enzyme immunoassay. The mRNA of S100A8 was expressed in the parenchyma and teat, leukocytes isolated from blood, and milk somatic cells. Antimicrobial peptide S100A8 was immunolocalized in the outermost layer of the teat skin of udders with and without LPS infusion, whereas in the mammary gland it was immunolocalized only in the leukocytes infiltrated in the alveoli after LPS infusion. Antimicrobial peptide S100A8 was also immunolocalized in the blood and milk leukocytes. The number of S100A8-positive cells in milk was higher than that in blood. The concentration of S100A8 in milk increased significantly at 72 h after intramammary infusion of LPS. These results suggest that S100A8 is produced in the leukocytes and that its secretion into milk is affected by LPS stimulation.

Bovine mastitis is an inflammation of the mammary glands caused by pathogenic invasion, and is known to have significant economic repercussions in the dairy industry (Hogeveen, Huijps, & Lam, 2011; Seegers, Fourichon, & Beaudeau, 2003). Mastitis can be caused by several bacterial species, such as those belonging to Staphylococcus, Streptococcus, and Enterobacteriaceae (Thomas et al., 2015). In addition, some causative pathogens of mastitis, such as Staphylococcus aureus, threaten public health, because a contamination of dairy products by these bacteria or their enterotoxins can lead to foodborne illnesses (Bianchi et al., 2014; Johler et al., 2018). The innate immune functions protect bovine mammary glands against pathogens. Antimicrobial components, including lactoferrin (LF), lingual antimicrobial peptide (LAP), and psoriasin (S100A7), which are components of the innate immune system, are synthesized in bovine mammary glands (Isobe, 2017). LF synthesized in the mammary epithelium and leukocytes inhibits bacterial growth, due to its high affinity to iron molecules (Huang, Morimoto, Hosoda,