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.

FcεR1-expressing neutrophils accumulate in the brain of mice infected with Plasmodium berghei (PbANKA) and promote the development of experimental cerebral malaria.

From the inoculation of Plasmodium sporozoites via Anopheles mosquito bites to the development of blood-stage parasites, a hallmark of the host response is an inflammatory reaction characterized by elevated histamine levels in the serum and tissues. Given the proinflammatory and immunosuppressive activities associated with histamine, we postulated that this vasoactive amine participates in malaria pathogenesis. Combined genetic and pharmacologic approaches demonstrated that histamine binding to H1R and H2R but not H3R and H4R increases the susceptibility of mice to infection with Plasmodium. To further understand the role of histamine in malaria pathogenesis, we used histidine decarboxylase–deficient (HDC−/−) mice, which are free of histamine. HDC−/− mice were highly resistant to severe malaria whether infected by mosquito bites or via injection of infected erythrocytes. HDC−/− mice displayed resistance to two lethal strains: Plasmodium berghei (Pb) ANKA, which triggers cerebral malaria (CM), and Pb NK65, which causes death without neurological symptoms. The resistance of HDC−/− mice to CM was associated with preserved blood–brain barrier integrity, the absence of infected erythrocyte aggregation in the brain vessels, and a lack of sequestration of CD4 and CD8 T cells. We demonstrate that histamine-mediated signaling contributes to malaria pathogenesis. Understanding the basis for these biological effects of histamine during infection may lead to novel therapeutic strategies to alleviate the severity of malaria.

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.Electronic supplementary materialThe online version of this article (doi:10.1186/s13567-015-0201-4) contains supplementary material, which is available to authorized users.

Mastitis remains a major infection of dairy cows and an important issue for dairy farmers and the dairy industry, in particular infections due to Escherichia coli strains. So far, properties specific to E. coli causing mastitis remain ill defined. In an attempt to better understand the properties required for E. coli to trigger mastitis, we used a range of in vitro assays to phenotypically characterize four E. coli strains, including the prototypical E. coli mastitis strain P4, possessing different relative abilities to cause mastitis in a mouse model. Our results indicate that a certain level of serum resistance might be required for colonization of the mammary gland. Resistance to neutrophil killing is also likely to contribute to a slower clearance of bacteria and higher chances to colonize the udder. In addition, we show that the four different strains do induce a pro-inflammatory response by mammary epithelial cells but with different intensities. Interestingly, the prototypical mastitis strain P4 actually induces the less intense response while it is responsible for the most severe infections in vivo. Altogether, our results suggest that different strategies can be used by E. coli strains to colonize the mammary gland and cause mastitis.

Despite the development of novel therapies, inflammatory bowel diseases remain an innovative treatment challenge. Helminth therapy is a new promising approach, and a key issue is the identification of helminth-derived anti-inflammatory mediators. P28 glutathione-S-transferase (P28GST), a protein derived from schistosomes, a trematode parasitic helminth, was shown to reduce intestinal inflammation in experimental colitis by down-regulating the Th1/Th17 response. In this multicenter, open-label, pilot Phase 2a study, we evaluated the safety of P28GST administered to patients with mild Crohn's disease (CD). We enrolled 10 patients with a baseline Crohn's disease activity index (CDAI) value <220. Eight patients received two to three subcutaneous injections of recombinant P28GST with adjuvant. This three-month treatment was followed by a nine-month monitoring period. The primary endpoints were the monthly rate and seriousness of adverse events (AEs). Secondary endpoints were clinical recurrence, assessed with the CDAI as well as the levels of immunologic and inflammatory blood and tissue markers. The most common AEs were local or regional events at the injection site and gastrointestinal disorders. At three months after the first injection, CDAI scores and blood calprotectin levels decreased in parallel. These results indicate that P28GST showed promise as a safe and new therapeutic option for treating CD.

The cytokine IL-17A has been shown to play critical roles in host defense against bacterial and fungal infections at different epithelial sites, but its role in the defense of the mammary gland (MG) has seldom been investigated, although infections of the MG constitute the main pathology afflicting dairy cows. In this study, we showed that IL-17A contributes to the defense of the MG against Escherichia coli infection by using a mouse mastitis model. After inoculation of the MG with a mastitis-causing E. coli strain, the bacterial load increased rapidly, triggering an intense influx of leukocytes into mammary tissue and increased concentrations of IL-6, IL-22, TNF-α, and IL-10. Neutrophils were the first cells that migrated intensely to the mammary tissue, in line with an early production of CXCL2. Depletion of neutrophils induced an increased mammary bacterial load. There was a significant increase of IL-17–containing CD4+ αβ T lymphocyte numbers in infected glands. Depletion of IL-17A correlated with an increased bacterial colonization and IL-10 production. Intramammary infusion of IL-17A at the onset of infection was associated with markedly decreased bacterial numbers, decreased IL-10 production, and increased neutrophil recruitment. Depletion of CD25+ regulatory T cells correlated with a decreased production of IL-10 and a reduced bacterial load. These results indicate that IL-17A is an important effector of MG immunity to E. coli and suggest that an early increased local production of IL-17A would improve the outcome of infection. These findings point to a new lead to the development of vaccines against mastitis.

SummaryPlasmodium spp., which causes malaria, produces a histamine-releasing factor (HRF), an orthologue of mammalian HRF. Histamine-releasing factor produced by erythrocytic stages of the parasite is thought to play a role in the pathogenesis of severe malaria. Here, we show in a rodent model that HRF is not important during the erythrocytic but pre-erythrocytic phase of infection, which mainly consists in the transformation in the liver of the mosquito-injected parasite form into the erythrocyte-infecting form. Development of P. berghei ANKA cl15cy1 liver stages lacking HRF is impaired and associated with an early rise in systemic IL-6, a cytokine that strongly suppresses development of Plasmodium liver stages. The defect is rescued by injection of anti-IL-6 antibodies or infection in IL-6-deficient mice and parasite HRF is sufficient to decrease IL-6 synthesis, indicating a direct role of parasite HRF in reducing host IL-6. The target cells modulated by HRF for IL-6 production at early time points during liver infection are neutrophils. Parasite HRF is thus used to down-regulate a cytokine with anti-parasite activity. Our data also highlight the link between a prolonged transition from liver to blood-stage infection and reduced incidence of experimental cerebral malaria.