Neutrophil recruitment in endotoxin-induced murine mastitis is strictly dependent on mammary alveolar macrophagesSharon Elazar1, Erez Gonen1, Ayala Livneh-Kol1, Ilan Rosenshine2 and Nahum Yehuda Shpigel1
1 The Koret School of Veterinary Medicine, Faculty of Agriculture, The Hebrew University of Jerusalem, POB 12, Rehovot 76100, Israel
2 Department of Microbiology and Molecular Genetics, IMRIC, Faculty of Medicine, The Hebrew University of Jerusalem, POB 12272, Jerusalem 91120, Israel
Received 14 July 2009; accepted 7 October 2009; published online 14 October 2009
Abstract - Mastitis, inflammation of the mammary tissue, is a common disease in dairy animals and mammary pathogenic Escherichia coli (MPEC) is a leading cause of the disease. Lipopolysaccharide (LPS) is an important virulence factor of MPEC and inoculation of the mammary glands with bacterial LPS is sufficient to induce an inflammatory response. We previously showed using adoptive transfer of normal macrophages into the mammary gland of TLR4-deficient C3H/HeJ mice that LPS/TLR4 signaling on mammary alveolar macrophages is sufficient to elicit neutrophil recruitment into the alveolar space. Here we show that TLR4-normal C3H/HeN mice, depleted of alveolar macrophages, were completely refractory to LPS intramammary challenge. These results indicate that alveolar macrophages are both sufficient and essential for neutrophil recruitment elicited by LPS/TLR4 signaling in the mammary gland. Using TNF gene-knockout mice and adoptive transfer of wild-type macrophages, we show here that TNF produced by mammary alveolar macrophages in response to LPS/TLR4 signaling is an essential mediator eliciting blood neutrophil recruitment into the milk spaces. Furthermore, using the IL8 receptor or IL1 receptor geneknockout mice we observed abrogated recruitment of neutrophils into the mammary gland and their entrapment on the basal side of the alveolar epithelium in response to intramammary LPS challenge. Adoptive transfer of wild-type neutrophils to IL1 receptor knockout mice, just before LPS challenge, restored normal neutrophil recruitment into the milk spaces. We conclude that neutrophil recruitment to the milk spaces is: (i) mediated through TNF, which is produced by alveolar macrophages in response to LPS/ TLR4 signaling and (ii) is dependent on IL8 and IL1 signaling and regulated by iNOS-derived NO.
Key words: mastitis / lipopolysaccharide / macrophage / neutrophil / murine model
Corresponding author: firstname.lastname@example.org
© INRA, EDP Sciences 2009