PTX3 is up-regulated in epithelial mammary cells during S. Aureus intramammary infection in goat

Pentraxins are a superfamily of conserved molecules with immune functions such as complement activation and opsonization. PTX3 is the prototypic long pentraxin and is produced by different cell populations (dendritic cells, monocytes/macrophages, endothelium, fibroblasts) after proinflammatory stimuli (TLR ligands, IL-1, TNF). Different studies have demonstrated the up-regulation of PTX3 during ruminant mastitis, but its role is still unknown. To better understand the role of PTX3 we investigated its pattern of expression in a model of S. aureus intramammary infection. Healthy goats were infused with PBS in the right udder and with S. aureus in the left udder and mammary biopsies were collected 30 h post infection. We first studied PTX3 pattern of expression in goat normal tissues. Then we investigated the role of PTX3 during mammary infection, comparing its expression in healthy and infected blood, milk and tissues. PTX3 mRNA was expressed at high level in bone marrow, mammary gland, aorta, pancreas, skin and lung. In mammary tissue PTX3 was mainly expressed in the apical cytoplasmic portion of mammary epithelial cells (MEC) and in macrophages. During S. aureus infection PTX3 was up-regulated by MEC. Moreover, PMNs recruited during infection were variably intensely positive. PTX3 mRNA expression was low in healthy tissues, indeed the molecule is commonly induced after proinflammatory stimulation. As expected, PTX3 was constitutively expressed in bone marrow, rich in PMNs and monocytes, in aorta covered by endothelium and in the skin. PTX3 was up-regulated in epithelial mammary cells and in milk cells after S. aureus infection, demonstrating that it represents a first line of immune defense in goat udder.