Essential role of neutrophils but not mammary alveolar macrophages in a murine model of acuteEscherichia colimastitis

Abstract

Mastitis, the inflammation of the mammary gland, is an important disease affecting dairy animals worldwide. The disease is caused by mammary pathogenic bacteria and Escherichia coli are frequently implicated. Virulence factors of mammary pathogenic E. coli are only partially known and intramammary challenge with LPS elicits neutrophil recruitment in experimental bovine and murine mastitis models. We have previously shown that neutrophil recruitment in LPS-induced murine mastitis is strictly dependent on mammary alveolar macrophages. However, the relative role of alveolar macrophages and blood neutrophils in E. coli mastitis is not well defined. To this end, we selectively depleted mammary alveolar macrophages or blood neutrophils before intramammary challenge with E. coli strain P4 (ECP4). Mice depleted of alveolar macrophages prior to intramammary challenge recruited neutrophils normally and restricted bacterial growth and interstitial invasion. Importantly however, upon depletion of alveolar macrophages, ECP4 invaded the mammary alveolar epithelial cells and formed intracellular bacterial communities. In contrast, neutrophil depletion prior to intramammary infection with ECP4 was associated with unrestricted bacterial growth, tissue damage, severe sepsis and mortality. This study suggests that neutrophils but not alveolar macrophages provide essential antimicrobial defense against mammary pathogenic E. coli. Furthermore, we show here similar invasion after depletion of alveolar macrophages as in our previous studies showing that LPS/TLR4 signaling on alveolar macrophages abrogates ECP4 invasion of the mammary epithelium. Interestingly, similar ECP4 invasion and formation of intracellular communities were also observed following intramammary infection of either iNOS gene-deficient or IL-1 receptor type 1 gene-deficient mice.

IL-17A Is an Important Effector of the Immune Response of the Mammary Gland to Escherichia coli Infection

“…4). This observation corroborates the important role of neutrophils early in the course of infection, as reported for E. coli mastitis in the cow (48) and the mouse mastitis model (18). Our data suggest that IL-17A contributed to bacterial containment and neutrophil recruitment only after the initial 24-h period.…”

“…2), and the depletion experiment confirmed that neutrophils are important for the control of infection in our model (Fig. 4), as previously shown by others (18). The early influx of neutrophils was paralleled by an early increase in MIP-2a, a chemokine that attracts neutrophils.…”

“…Lately this model has been used to investigate the pathogenesis of E. coli mastitis with different mouse lines and E. coli strains. Neutrophils were shown to play an essential role in MG defense, in relation to the production of the chemokines CXCL1 (KC) and CXCL2 (MIP-2) (18). The proinflammatory chemokines TNF-a and IL-1b were produced at low or high concentrations in the mammary tissue according to the reports (18)(19)(20), but information on other cytokines and their cellular sources is still lacking.…”

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

“…This inflammation response pointing out to additional factors beyond LPS and additional cells beyond alveolar macrophages play a role in the inflammatory response to E. coli. It has been suggested that in the absence of functional TLR4 the infecting E. coli P4 invaded epithelial cells with high efficiency, forming intracellular microcolonies, since invasion of epithelial cells by E. coli is limited by alveolar macrophages using a process dependent on TLR4 signaling (Gonen et al, 2007;Elazar et al, 2010b;Schukken et al, 2011).…”

Viabilidade celular, fagocitose e espraiamento de fagócitos mononucleares, e liberação de peróxido de hidrogênio por leucócitos de glândulas mamárias bovinas sadias e infectadas

“…Atribui-se aos leucócitos polimorfonucleares (PMNL) a maior responsabilidade na proteção da glândula mamária aos patógenos invasores (Paape et al 2003, Elazar et al 2010. Entretanto, deve-se considerar a delicada inter-relação que rege os mecanismos imunes, e o papel crucial dos macrófagos na detecção e montagem da resposta imune, e consequentemente nos mecanismos de defesa da glândula mamária (Della Libera et al 2006).…”