Immunomediator and milk protein gene expression in mammary tissue during endotoxin-induced mastitis

Abstract

Mammary gland infection induces an inflammatory reaction which causes an increase of somatic cells in milk and activation of bacteriostatic enzymes and proteins in milk. It has been demonstrated that during spontaneously occurring subclinical mastitis the somatic milk cells, mainly macrophages, secrete cytokines, eicosanoids, acute phase proteins and other immunomediators. In contrast, the bacteriostatic protein lactoferrin is mainly secreted by mammary epithelial tissue, while major milk proteins like α-lactalbumin and κ-casein are down-regulated already during subclinical infection. In LPS-challenged quarters, tumor necrosis factor α (TNF-α), interleukin-1β (IL-1β) and cyclooxygenase-2 expression increased to highest values at 3 h after LPS-challenge. Expression of lactoferrin, lysozyme, inducible nitric oxide synthase, l-selectin, NFκB and of the apoptotic factors caspase-3, caspase-7 and Fas (FS-7 associated surface antigen) was elevated and peaked at 6 h after challenge. No significant increase in expression of platelet-activating factor, acethylhydrolase, 5-lipoxygenase, β-integrin and insulin-like growth factor 1 was found. In the control quarters, only TNF-α, IL-1β and lysozyme increase slightly and much less than in LPS-challenged quarters whereas the other parameters tested did not change significantly. Gene expression of major milk proteins did not change significantly in response to the LPS challenge (αS1-casein (CN), αS2-CN, β-CN and β-lactoglobulin) except for α-lactalbumin which decreased in LPS-treated and control quarters and for κ-CN which decreased in the LPS-treated quarters. In conclusion, gene expression of the majority albeit not all inflammatory factors changed within hours of LPS challenge. Decreased gene expression of α-lactalbumin and κ-CN may reduce milk yield and suitability for cheese production.