Bacterial lipopolysaccharide stimulates bovine neutrophil production of TNF-α, IL-1β, IL-12 and IFN-γ

After intramammary infection, polymorphonuclear neutrophil leukocytes (PMN) are the first cells recruited into the mammary gland. Rapid recruitment of and bacterial phagocytosis and killing by PMN are the most effective defenses against establishment of bacterial infection. In addition to their phagocytic and bactericidal properties, PMN may play a key supportive role through secretion of cytokines during the innate immune response. We sought to determine whether bovine PMN produce cytokines in response to stimulation by lipopolysaccharide (LPS). To investigate the effects of LPS on the expression of cytokines secreted by bovine PMN, we measured the expression of tumor necrosis factor (TNF)-$\alpha $, interleukin (IL)-1$\beta $, IL-12, and interferon (IFN)-$\gamma $ by ELISA after stimulation with different concentrations of LPS, and secretion of IL-8 after co-stimulation with LPS and either TNF-$\alpha $ or IL-1$\beta $. Bovine PMN were shown to secrete TNF-$\alpha $, IL-1$\beta $, IL-12, IL-8 and IFN-$\gamma $ in response to LPS. Co-incubation of PMN with LPS and TNF-$\alpha $ increased secretion of IL-8 when compared to LPS alone. It was concluded that LPS stimulation up-regulates the secretion of cytokines by bovine PMN, and that co-incubation of LPS with TNF-$\alpha $ had an additive effect on the secretion of IL-8. These data show that bovine PMN, in addition to their phagocytic and bactericidal properties, may play a supportive role in the innate immune response to infection by Gram-negative bacteria through their ability to produce immuno-regulating cytokines.