Neutrophil recruitment in endotoxin-induced murine mastitis is strictly dependent on mammary alveolar macrophages

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 TNFα gene-knockout mice and adoptive transfer of wild-type macrophages, we show here that TNFα 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 gene-knockout 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 TNFα, which is produced by alveolar macrophages in response to LPS/TLR4 signaling and (ii) is dependent on IL8 and IL1β signaling and regulated by iNOS-derived NO.

The Innate Immunity in Bovine Mastitis: The Role of Pattern-Recognition Receptors

“…It was shown that the expression 25-hydroxyvitamin D3 1α-hydrolase was significantly increased in tissue and cells from of infected mammary glands and was predominantly expressed in CD14 + cells (Nelson et al, 2010), which is expressed in both neutrophils and macrophages in milk (Paape et al, 1996). Thus, regarding the importance of innate immunity for mammary gland health Rainard and Riollet, 2006;Elazar et al, 2010a;, efforts to find …”

Polydatin ameliorates Staphylococcus aureus-induced mastitis in mice via inhibiting TLR2-mediated activation of the p38 MAPK/NF-κB pathway

“…Thus, once mammary gland tissues are infected by S aureus, it is extremely difficult to control and eliminate the infection [5] . It has been well established that recognition of the infection through activation of pattern recognition receptors (PRRs) is necessary for initiating the immune response when mammary glands are infected by S aureus [6] . PRRs are considered crucial in the survival of the pathogen, and they recognize pathogenassociated molecular patterns (PAMPs) [7,8] .…”

Brazilin plays an anti-inflammatory role with regulating Toll-like receptor 2 and TLR 2 downstream pathways in Staphylococcus aureus-induced mastitis in mice

“…Once S. aureus infects the mammary glands, recognizing the infection via activation of pattern recognition receptors (PRRs) is imperative for the initiation of the immune response in the mammary glands [11]. Toll-like receptor 2 (TLR2), a PRR receptor, is activated by peptidoglycan and lipoteichoic acid, which are major constituents of the cell wall pathogen-associated molecular pattern (PAMP) of gram-positive bacteria, including S. aureus [12].…”