Critical appraisal of vaccine approaches to control bovine mastitis

Despite their interest to combat mastitis, vaccines are few and underused, owing to limited efficacy. The mammary gland may have established with its pathogens a modus vivendi that favours the settlement of chronic subclinical infections. Reprogramming this immune response in a way that favours bacteriological cure but spares the secretory function presents a major challenge to immunologists. To improve vaccine efficacy, stress should be put on research on T lymphocyte-dependent immune defenses. In this view, improved knowledge of mammary lymphocyte populations, in association with systems vaccinology approaches, should offer new prospects for the development of efficient vaccines.Les vaccins contre les mammites sont peu nombreux à être commercialisés et peu utilisés en raison d’une efficacité limitée. Il semble que la mamelle ait établi avec ses agents pathogènes un modus vivendi qui favorise le maintien d’infections chroniques subcliniques. La reprogrammation de cette immunité par la vaccination dans un sens favorisant l’élimination des infections sans compromettre la fonction sécrétoire pose un défi majeur aux immunologistes. Pour améliorer l’efficacité des vaccins, les défenses immunitaires dépendantes des lymphocytes T ne devraient plus être négligées. Dans cette optique, une meilleure connaissance des populations lymphocytaires mammaires, associée aux approches de la vaccinologie systématique, devrait offrir de nouvelles perspectives de développement de vaccins efficaces

A Critical Appraisal of Probiotics for Mastitis Control

The urge to reduce antimicrobials use in dairy farming has prompted a search for alternative solutions. As infections of the mammary gland is a major reason for antibiotic administration to dairy ruminants, mammary probiotics have recently been presented as a possible alternative for the treatment of mastitis. To assess the validity of this proposal, we performed a general appraisal of the knowledge related to probiotics for mammary health by examining their potential modes of action and assessing the compatibility of these mechanisms with the immunobiology of mammary gland infections. Then we analyzed the literature published on the subject, taking into account the preliminary in vitro experiments and the in vivo trials. Preliminary experiments aimed essentially at exploring in vitro the capacity of putative probiotics, mainly lactic acid bacteria (LABs), to interfere with mastitis-associated bacteria or to interact with mammary epithelial cells. A few studies used LABs selected on the basis of bacteriocin production or the capacity to adhere to epithelial cells to perform in vivo experiments. Intramammary infusion of LABs showed that LABs are pro-inflammatory for the mammary gland, inducing an intense influx of neutrophils into milk during lactation and at drying-off. Yet, their capacity to cure mastitis remains to be established. A few preliminary studies tackle the possibility of using probiotics to interfere with the teat apex microbiota or to prevent the colonization of the teat canal by pathogenic bacteria. From the analysis of the published literature, it appears that currently there is no sound scientific foundation for the use of probiotics to prevent or treat mastitis. We conclude that the prospects for oral probiotics are not promising for ruminants, those for intramammary probiotics should be considered with caution, but that teat apex probiotics deserve further research

Repertoire of Escherichia coli agonists sensed by innate immunity receptors of the bovine udder and mammary epithelial cells

Escherichia coli is a frequent cause of clinical mastitis in dairy cows. It has been shown that a prompt response of the mammary gland after E. coli entry into the lumen of the gland is required to control the infection, which means that the early detection of bacteria is of prime importance. Yet, apart from lipopolysaccharide (LPS), little is known of the bacterial components which are detected by the mammary innate immune system. We investigated the repertoire of potential bacterial agonists sensed by the udder and bovine mammary epithelial cells (bMEC) during E. coli mastitis by using purified or synthetic molecular surrogates of bacterial agonists of identified pattern-recognition receptors (PRRs). The production of CXCL8 and the influx of leucocytes in milk were the readouts of reactivity of stimulated cultured bMEC and challenged udders, respectively. Quantitative PCR revealed that bMEC in culture expressed the nucleotide oligomerization domain receptors NOD1 and NOD2, along with the Toll-like receptors TLR1, TLR2, TLR4, and TLR6, but hardly TLR5. In line with expression data, bMEC proved to react to the cognate agonists C12-iE-DAP (NOD1), Pam3CSK4 (TLR1/2), Pam2CSK4 (TLR2/6), pure LPS (TLR4), but not to flagellin (TLR5). As the udder reactivity to NOD1 and TLR5 agonists has never been reported, we tested whether the mammary gland reacted to intramammary infusion of C12-iE-DAP or flagellin. The udder reacted to C12-iE-DAP, but not to flagellin, in line with the reactivity of bMEC. These results extend our knowledge of the reactivity of the bovine mammary gland to bacterial agonists of the innate immune system, and suggest that E. coli can be recognized by several PRRs including NOD1, but unexpectedly not by TLR5. The way the mammary gland senses E. coli is likely to shape the innate immune response and finally the outcome of E. coli mastitis

Differential response of bovine mammary epithelial cells to Staphylococcus aureus or Escherichia coli agonists of the innate immune system

Mastitis caused by Escherichia coli and Staphylococcus aureus is a major pathology of dairy cows. To better understand the differential response of the mammary gland to these two pathogens, we stimulated bovine mammary epithelial cells (bMEC) with either E. coli crude lipopolysaccharide (LPS) or with S. aureus culture supernatant (SaS) to compare the transcriptomic profiles of the initial bMEC response. By using HEK 293 reporter cells for pattern recognition receptors, the LPS preparation was found to stimulate TLR2 and TLR4 but not TLR5, Nod1 or Nod2, whereas SaS stimulated TLR2. Biochemical analysis revealed that lipoteichoic acid, protein A and alpha-hemolysin were all present in SaS, and bMEC were found to be responsive to each of these molecules. Transcriptome profiling revealed a core innate immune response partly shared by LPS and SaS. However, LPS induced expression of a significant higher number of genes and the fold changes were of greater magnitude than those induced by SaS. Microarray data analysis suggests that the activation pathways and the early chemokine and cytokine production preceded the defense and stress responses. A major differential response was the activation of the type I IFN pathway by LPS but not by SaS. The higher upregulation of chemokines (Cxcl10, Ccl2, Ccl5 and Ccl20) that target mononuclear leucocytes by LPS than by SaS is likely to be related to the differential activation of the type I IFN pathway, and could induce a different profile of the initial recruitment of leucocytes. The MEC responses to the two stimuli were different, as LPS was associated with NF-kappaB and Fas signaling pathways, whereas SaS was associated with AP-1 and IL-17A signaling pathways. It is noteworthy that at the protein level secretion of TNF-alpha and IL-1beta was not induced by either stimulus. These results suggest that the response of MEC to diffusible stimuli from E. coli and S. aureus contributes to the onset of the response with differential leucocyte recruitment and distinct inflammatory and innate immune reactions of the mammary gland to infection

Investigating the contribution of IL-17A and IL-17F to the host response during Escherichia coli mastitis

Mastitis remains a major disease of cattle with a strong impact on the dairy industry. There is a growing interest in understanding how cell mediated immunity contributes to the defence of the mammary gland against invading mastitis causing bacteria. Cytokines belonging to the IL-17 family, and the cells that produce them, have been described as important modulators of the innate immunity, in particular that of epithelial cells. We report here that expression of IL-17A and IL-17F genes, encoding two members of the IL-17 family, are induced in udder tissues of cows experimentally infected with Escherichia coli. The impact of IL-17A on the innate response of bovine mammary epithelial cells was investigated using a newly isolated cell line, the PS cell line. We first showed that PS cells, similar to primary bovine mammary epithelial cells, were able to respond to agonists of TLR2 and to LPS, provided CD14 was added to the culture medium. We then showed that secretion of CXCL8 and transcription of innate immunity related-genes by PS cells were increased by IL-17A, in particular when these cells were stimulated with live E. coli bacteria. Together with data from the literature, these results support the hypothesis that IL-17A and IL-17 F could play an important role in mediating of host-pathogen interactions during mastitis

Differential Transcriptional Response To Staphylococcus aureus Infection In Two Divergent Lines Of Sheep Selected On Milk Somatic Cell Score

The milk somatic cell score (SCS) is an indirect indicator of mastitis, currently used as a selection criterion of dairy ruminants that leads to decreased intra-mammary infection prevalence. In the present study, gene expression profiles after Staphylococcus stimulations were determined in three cell types of mastitis resistant and susceptible ewes. The comparisons of the lists of the differentially-expressed genes allowed identification of commonly-regulated genes among cell types. These results lead to identify a subset of genes involved in pathogen-related receptor signaling. These genes may play an important role in recognition of pathogens and may improve resistance to intramammary infections

Issues and special features of animal health research

In the rapidly changing context of research on animal health, INRA launched a collective discussion on the challenges facing the field, its distinguishing features, and synergies with biomedical research. As has been declared forcibly by the heads of WHO, FAO and OIE, the challenges facing animal health, beyond diseases transmissible to humans, are critically important and involve food security, agriculture economics, and the ensemble of economic activities associated with agriculture. There are in addition issues related to public health (zoonoses, xenobiotics, antimicrobial resistance), the environment, and animal welfare

Infections mammaires : une immunité protectrice ?

National audienceWe know that mastitis does not protect against recurrence, which might suggest that udder infections do not induce protective immunity. However, it would be incorrect to say that mastitis does not induce an immune response.The udder is equipped to develop adaptive immune responses to infections. However, the immune response is conditioned by the fact that the pathogens responsible for mastitis are members of the skin, respiratory or digestive microbiota of ruminants. In addition, the aggressiveness of the response must be curbed in order to maintain the physiological function of the udder, which leads to a non-sterilizing homeostatic immunity. Finally, the pathogenic bacteria have adapted to the udder during a long co-evolution, and have developed escape strategies, in particular by reducing their virulence. Under these conditions, is it possible to do better than evolution, by vaccination, at the risk of upsetting the balance that protects the secretory function of the udder? The udder being an organ with a strong regenerative power, it can allow itself an intense immune response, which, if it induces a decrease in the bacterial load and a bacteriological cure, will ultimately be beneficial to the secretory function of the udder.Les mammites ne protègent pas des récidives, ce qui pourrait faire penser que les infections mammaires n’induisent pas d’immunité protectrice.Il serait cependant inexact de dire que les infections n'induisent pas de réponse immunitaire.La mamelle est équipée pour développer des réponses immunitaires adaptatives aux infections. Mais la réponse immunitaire est conditionnée par le fait que les pathogènes responsables de mammite sont des bactéries des microbiotes cutané, respiratoire ou digestif des ruminants.De plus, l’agressivité de la réponse doit être réfrénée de façon à conserver la fonction physiologique de la mamelle, ce qui débouche sur une immunité homéostatique non stérilisante.Enfin, les bactéries pathogènes se sont adaptées à la mamelle au cours d’une longue coévolution, et ont développé des stratégies d’échappement, notamment en réduisant leur virulence. Dans ces conditions, est-il possible de faire mieux que l’évolution, par la vaccination, au risque de rompre l’équilibre qui ménage la fonction sécrétoire de la mamelle ? La mamelle étant un organe à fort pouvoir régénérateur, elle peut se permettre une réponse immunitaire intense, qui, si elle induit une baisse de la charge bactérienne et une guérison bactériologique, sera à terme bénéfique à la fonction sécrétoire de la mamelle

Cellules dans la mamelle et dans le lait : quels rôles pour la maîtrise des mammites ?

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