Characterization of immune response in Staphylococcus aureus chronically infected bovine mammary glands during active involution

Abstract

The aim of this study was to characterize the immune response in Staphylococcus aureus chronicallyinfected bovine mammary glands during active involution. Twenty-one Holstein non-pregnant cows inlate lactation either uninfected or with chronic naturally acquired S. aureus intramammary infections(IMI) were included in this study. Cows were slaughtered at 7, 14 and 21 d after cessation of milkingand samples for immunohistochemical analysis were taken. Protein expression of toll-like receptor 2(TLR2) and TLR4 was significantly higher in S. aureus-infected quarters than in uninfected controls atthe three involution stages studied. Protein expression of tumor necrosis factor-alpha (TNF-á),interleukin (IL)-1á and IL-17 was significantly affected by IMI; being higher in S. aureus-infectedthan uninfected quarters during all evaluated stages. In S. aureus-infected and uninfected quartersprotein expression of lactoferrin increased from day 7 to 14 of involution, decreasing significantly today 21 in mammary quarters with chronic infections. The number of monocytes-macrophages wassignificantly higher in S. aureus-infected than in uninfected control quarters at 7 and 21 d ofinvolution. The number of T lymphocytes was significantly higher in S. aureus-infected than inuninfected quarters at 7 and 14 d of involution while the number of B lymphocytes was significantlyhigher in S. aureus-infected than in uninfected quarters during all evaluated stages, showing aprogressive increase as involution advanced. These results demonstrated a sustained and exacerbatedinnate and adaptive immune response during chronic S. aureus IMI, playing a critical role in theinfection control during active involution