Innate immunity of the bovine mammary gland

Functional adaptations of the transcriptome to mastitis-causing pathogens: the mammary gland and beyond

Application of microarrays to the study of intramammary infections in recent years has provided a wealth of fundamental information on the transcriptomics adaptation of tissue/cells to the disease. Due to its heavy toll on productivity and health of the animal, in vivo and in vitro transcriptomics works involving different mastitis-causing pathogens have been conducted on the mammary gland, primarily on livestock species such as cow and sheep, with few studies in non-ruminants. However, the response to an infectious challenge originating in the mammary gland elicits systemic responses in the animal and encompasses tissues such as liver and immune cells in the circulation, with also potential effects on other tissues such as adipose. The susceptibility of the animal to develop mastitis likely is affected by factors beyond the mammary gland, e.g. negative energy balance as it occurs around parturition. Objectives of this review are to discuss the use of systems biology concepts for the holistic study of animal responses to intramammary infection; providing an update of recent work using transcriptomics to study mammary and peripheral tissue (i.e. liver) as well as neutrophils and macrophage responses to mastitis-causing pathogens; discuss the effect of negative energy balance on mastitis predisposition; and analyze the bovine and murine mammary innate-immune responses during lactation and involution using a novel functional analysis approach to uncover potential predisposing factors to mastitis throughout an animal's productive life.

Effect of Escherichia coli lipopolysaccharide on u-PA activity and u-PA and u-PAR RNA expression in a bovine mammary epithelial cell line

It is well known that the plasminogen-activating (PA) system plays a key role in the bovine mammary gland during tissue remodelling. However, the modulation of the PA cascade after bacterial infections needs to be elucidated. This study examined the effects of Escherichia coli lipopolysaccharide (LPS) on cell viability, the modulation of cell-associated u-PA activity, and the regulation of u-PA and u-PA receptor (u-PAR) RNA expression using the BME-UV1 bovine mammary epithelial cell line. LPS did not affect cell viability, but induced an increase in u-PA activity, with the maximum response after 6 h of incubation. Moreover, u-PA and u-PAR mRNA expression were both up-regulated in BME-UV1 cells after 3 h of incubation with LPS. These data indicated that E. coli LPS led to an increase in u-PA activity and RNA expression of u-PA and u-PAR in BME-UV1 cells, thus strengthening the role of the PA system during pathological processes.

Staphylococcal-associated molecular patterns enhance expression of immune defense genes induced by IL-17 in mammary epithelial cells

Interleukin-17A (IL-17A) and IL-17F have been shown to mediate a crucial crosstalk between the immune system and various epithelial tissues, stimulating various defensive mechanisms to bacterial infections. A number of studies have characterized the response to IL-17A and IL-17F of epithelial cells from airways, intestine, and skin, but not from the mammary gland. To evaluate the potential contribution of IL-17 to the immune defense of the mammary gland, we analyzed the effects of recombinant bovine IL-17A and IL-17F on primary bovine mammary epithelial cells (MEC) by quantitative PCR and ELISA. We found expression (mRNA) of the two components of the IL-17 receptor complex, IL-17RA and IL-17RC, in mammary tissue and MEC in vitro. The expression of a number of genes encoding cytokines, chemokines and proteins endowed with antibacterial activities was increased by IL-17A, and to a lesser extent by IL-17F, but the magnitude of responses was modest. As expected, responses were augmented by the combination of IL-17A or IL-17F with TNF-α. Interestingly, responses of a few of the tested genes, such as IL8, CCL20, iNOS, and CfB, were augmented by the combination of IL-17A with staphylococcal lipoteichoic acid or muramyl dipeptide, bacterial agonists of the innate immune system. This can be interpreted as indicating that IL-17A and IL-17F are tailored to exert their full potential in a septic environment. MEC responses were characterized by the expression of chemokines targeting not only neutrophils (CXCL3 and CXCL8) but also mononuclear leucocytes (CCL2, CCL20). Production of IL-6 was low and the inflammatory cytokines TNF-α and IL-1β were expressed (mRNA) but proteins were not secreted. Altogether, our results suggest that IL-17A and IL-17F have a potential to modulate the mammary gland immune response to mastitis-causing pathogens.

First evidence of the presence of genomic islands in Escherichia coli P4, a mammary pathogen frequently used to induce experimental mastitis

Mastitis pathogens belonging to Escherichia coli species are often considered as environmental opportunistic pathogens that invade the udder and are rapidly killed by the immune system of cows. However, several studies have reported that some of these strains are able to persist in the udder for prolonged periods or to adhere and invade mammary epithelial cells, suggesting that they might possess some specific properties or genes that could be involved in their capacity to provoke mastitis. The aim of this work was to search for such specific genes in the E. coli strain P4, which was isolated from a case of severe mastitis and is often used to induce experimental mastitis. We established that this strain belongs to phylogenetic group A of the E. coli species, and that its core genome is very similar to that of the commensal nonpathogenic strain E. coli K-12 MG1655. Seventeen transfer RNA loci, known to be frequently associated with genomic islands, were screened and an altered structure was detected for 7 of them. The partial characterization of 5 of these loci (asnT, leuX, pheV, serU, and thrW) and the complete characterization of 1 (argW) revealed the presence of genomic islands that differ from those already described in pathogenic or nonpathogenic E. coli strains.

Host-response patterns of intramammary infections in dairy cows

Many different bacterial species have the ability to cause an infection of the bovine mammary gland and the host response to these infections is what we recognize as mastitis. In this review we evaluate the pathogen specific response to the three main bacterial species causing bovine mastitis: Escherichia coli, Streptococcus uberis and Staphylococcus aureus. In this paper we will review the bacterial growth patterns, host immune response and clinical response that results from the intramammary infections. Clear differences in bacterial growth pattern are shown between bacterial species. The dominant pattern in E. coli infections is a short duration high bacteria count infection, in S. aureus this is more commonly a persistent infection with relative low bacteria counts and in S. uberis a long duration high bacteria count infection is often observed. The host immune response differs significantly depending on the invading bacterial species. The underlying reasons for the differences and the resulting host response are described. Finally we discuss the clinical response pattern for each of the three bacterial species. The largest contrast is between E. coli and S. aureus where a larger proportion of E. coli infections cause potentially severe clinical symptoms, whereas the majority of S. aureus infections go clinically unnoticed. The relevance of fully understanding the bovine host response to intramammary infection is discussed, some major gaps in our knowledge are highlighted and directions for future research are indicated.

Composition, indigenous proteolytic enzymes and coagulating behaviour of ewe milk as affected by somatic cell count

This study was undertaken to assess the effect of somatic cell count in ewe milk on i) composition and hygienic traits; ii) plasmin, cathepsin and elastase activities; iii) leukocyte differential count; iv) renneting parameters. Individual ewe milk samples were grouped according to somatic cell count (SCC) into five classes: SC300 (<300 000 cells/ml), SC500 (from 301 000 to 500 000 cells/ml), SC1000 (from 501 000 to 1 000 000 cells/ml), SC2000 (from 1 001 000 to 2 000 000 cells/ml) and SC>2000 (>2 001 000 cells/ml). Individual milk samples were analysed for pH, chemical composition, microbial features, indigenous proteolytic enzymes, differential leukocyte population, and renneting parameters. Milk yield, lactose, protein, non casein nitrogen, microbial features were affected by SCC level. Plasmin and elastase activities were the highest in samples with more than 1 000 000 cells/ml; plasmin had intermediate values in samples with 300 000 to 1 000 000 cells/ml and the lowest in samples with less than 300 000 cells/ml of milk. Cathepsin D showed significantly lower values in SC300 and SC1000 classes than in SC500, SC2000 and SC>2000 classes. The highest percentages of lymphocyte were found in samples with less than 1 000 000 cells/ml, while the highest levels of polymorphonuclear leukocyte were found in samples with more than 1 000 000 cells/ml of milk. Longer clotting time was found in SC>2000 samples, while reduced clot firmness was observed in SC500 and SC>2000 samples. Results on milk yield and on compositional parameters evidenced an impairment of udder efficiency in ewe milk samples starting from 300 000 cells/ml. Plasmin activity in milk can be considered as a marker of the synthetic and secreting ability of the mammary gland; furthermore plasmin and elastase were consistent with the health status of the udder. Finally cathepsin D played a role in the worsening of renneting properties of ewe milk.

Staphylococcus aureus inhibits nuclear factor kappa B activation mediated by prolactin in bovine mammary epithelial cells

The hormone prolactin (PRL) regulates differentiation and lactation in the bovine mammary epithelium. This tissue is especially prone to contracting mastitis, a disease characterized by an inflammatory response in the mammary gland. Staphylococcus aureus is the infectious agent primarily responsible for mastitis. In a previous study, we have shown that bovine PRL (bPRL) stimulates S. aureus internalization in bovine mammary epithelial cells (bMECs) by regulating several host innate immune elements, which are often modulated by nuclear factor kappa B (NF-κB). However, it is unknown whether the activation of the NF-κB transcription factor is regulated by bPRL during S. aureus internalization. The objective of this study was to determine the role of NF-κB in bPRL-stimulated bMECs during S. aureus internalization. Our results showed that bPRL (5 ng/ml) induced NF-κB activation in bMECs; however, it was inhibited by S. aureus in presence of the hormone. When we blocked NF-κB activation with acetylsalicylic acid, we detected an inhibition in S. aureus internalization (48%) in bPRL-stimulated bMECs. The infection-induced inhibition of NF-κB activation in the presence of bPRL correlates with the downregulation in bPRL-mediated tumor necrosis factor (TNF)-α (27%) and tracheal antimicrobial peptide (TAP, 70%) mRNA expression and nitric oxide (NO) production in bMECs. We also detected an inhibition in the expression of the bPRL target gene κ-casein (50%) under these conditions. Interestingly, these effects are not achieved through increased PRL receptor expression (PRLR), as it was inhibited (48%) compared to control cells. In conclusion, NF-κB activation in bMECs is inhibited by S. aureus in the presence of bPRL, suggesting a mechanism by which the host innate immune response may be compromised during subclinical mastitis.

Natural antibodies in bovine milk and blood plasma: variability among cows, repeatability within cows, and relation between milk and plasma titers

Innate immunity plays an important role in preventing (barrier function) or combating infection (effector function). An important humoral component of innate immunity is formed by natural antibodies (NAb). The objectives of this study were to determine presence, variation among cows and repeatability within cows over time of total NAb titers directed to the pathogen-associated molecular patterns lipopolysaccharide, lipoteichoic acid (LTA) and peptidoglycan, and titers of NAb directed to the glycoprotein keyhole limpet hemocyanin in milk and plasma of individual cows. Furthermore in milk the antibody isotypes IgG1, IgG2, IgM and IgA binding LTA were analyzed. Ten milk and blood samples were obtained from each of 20 clinically healthy dairy cows from first to seventh parity during a period of 3 weeks. Total NAb binding lipopolysaccharide, LTA, peptidoglycan, and keyhole limpet hemocyanin were detected in milk and plasma, with titers considerably higher in plasma than in milk. Total NAb titers showed significant variation among cows, and repeatability within cows over time (ranging from 0.60 to 0.93). Titers of NAb in milk and plasma were positively correlated (correlation ranging from 0.69 to 0.91). Natural antibodies in milk binding LTA were of all 4 isotypes tested, although IgG2 was on average only present at low titers. All 4 isotypes in milk binding LTA also showed variation among cows, and repeatability within cows over time (ranging from 0.84 to 0.92). We conclude that NAb can be measured in a consistent and repeatable manner in bovine milk and blood plasma.

Comparative expression profiling of E. coli and S. aureus inoculated primary mammary gland cells sampled from cows with different genetic predispositions for somatic cell score

Background

During the past ten years many quantitative trait loci (QTL) affecting mastitis incidence and mastitis related traits like somatic cell score (SCS) were identified in cattle. However, little is known about the molecular architecture of QTL affecting mastitis susceptibility and the underlying physiological mechanisms and genes causing mastitis susceptibility. Here, a genome-wide expression analysis was conducted to analyze molecular mechanisms of mastitis susceptibility that are affected by a specific QTL for SCS on Bos taurus autosome 18 (BTA18). Thereby, some first insights were sought into the genetically determined mechanisms of mammary gland epithelial cells influencing the course of infection.

Methods

Primary bovine mammary gland epithelial cells (pbMEC) were sampled from the udder parenchyma of cows selected for high and low mastitis susceptibility by applying a marker-assisted selection strategy considering QTL and molecular marker information of a confirmed QTL for SCS in the telomeric region of BTA18. The cells were cultured and subsequently inoculated with heat-inactivated mastitis pathogens Escherichia coli and Staphylococcus aureus, respectively. After 1, 6 and 24 h, the cells were harvested and analyzed using the microarray expression chip technology to identify differences in mRNA expression profiles attributed to genetic predisposition, inoculation and cell culture.

Results

Comparative analysis of co-expression profiles clearly showed a faster and stronger response after pathogen challenge in pbMEC from less susceptible animals that inherited the favorable QTL allele 'Q' than in pbMEC from more susceptible animals that inherited the unfavorable QTL allele 'q'. Furthermore, the results highlighted RELB as a functional and positional candidate gene and related non-canonical Nf-kappaB signaling as a functional mechanism affected by the QTL. However, in both groups, inoculation resulted in up-regulation of genes associated with the Ingenuity pathways 'dendritic cell maturation' and 'acute phase response signaling', whereas cell culture affected biological processes involved in 'cellular development'.

Conclusions

The results indicate that the complex expression profiling of pathogen challenged pbMEC sampled from cows inheriting alternative QTL alleles is suitable to study genetically determined molecular mechanisms of mastitis susceptibility in mammary epithelial cells in vitro and to highlight the most likely functional pathways and candidate genes underlying the QTL effect.

Udder pathogens and their resistance to antimicrobial agents in dairy cows in Estonia

Background

The goal of this study was to estimate the distribution of udder pathogens and their antibiotic resistance in Estonia during the years 2007-2009.

Methods

The bacteriological findings reported in this study originate from quarter milk samples collected from cows on Estonian dairy farms that had clinical or subclinical mastitis. The samples were submitted by local veterinarians to the Estonian Veterinary and Food Laboratory during 2007-2009. Milk samples were examined by conventional bacteriology. In vitro antimicrobial susceptibility testing was performed with the disc diffusion test. Logistic regression with a random herd effect to control for clustering was used for statistical analysis.

Results

During the study period, 3058 clinical mastitis samples from 190 farms and 5146 subclinical mastitis samples from 274 farms were investigated. Positive results were found in 57% of the samples (4680 out of 8204), and the proportion did not differ according to year (p > 0.05). The proportion of bacteriologically negative samples was 22.3% and that of mixed growth was 20.6%. Streptococcus uberis (Str. uberis) was the bacterium isolated most frequently (18.4%) from cases of clinical mastitis, followed by Escherichia coli (E. coli) (15.9%) and Streptococcus agalactiae (Str. agalactiae) (11.9%). The bacteria that caused subclinical mastitis were mainly Staphylococcus aureus (S. aureus) (20%) and coagulase-negative staphylococci (CNS) (15.4%). The probability of isolating S. aureus from milk samples was significantly higher on farms that had fewer than 30 cows, when compared with farms that had more than 100 cows (p < 0.005). A significantly higher risk of Str. agalactiae infection was found on farms with more than 600 cows (p = 0.034) compared with smaller farms. The proportion of S. aureus and CNS isolates that were resistant to penicillin was 61.4% and 38.5%, respectively. Among the E. coli isolates, ampicillin, streptomycin and tetracycline resistance were observed in 24.3%, 15.6% and 13.5%, respectively.

Conclusions

This study showed that the main pathogens associated with clinical mastitis were Str. uberis and E. coli. Subclinical mastitis was caused mainly by S. aureus and CNS. The number of S. aureus and Str. agalactiae isolates depended on herd size. Antimicrobial resistance was highly prevalent, especially penicillin resistance in S. aureus and CNS.

Ethyl pyruvate diminishes the endotoxin-induced inflammatory response of bovine mammary endothelial cells

The endotoxin-induced inflammatory response during coliform mastitis is difficult to control with the currently available therapeutics. Endothelial cells are among the first cell type to be engaged in the inflammatory response and can modulate the severity of inflammation by producing proinflammatory mediators upon endotoxin exposure. Ethyl pyruvate, an ethyl ester of pyruvic acid, can ameliorate endotoxin-induced inflammatory responses by inhibiting the production of proinflammatory mediators in several in vitro and in vivo endotoxemia models. The objective of this study was to determine the effect of ethyl pyruvate on the production of vascular proinflammatory mediators that are associated with the pathogenesis of coliform mastitis. The ability of ethyl pyruvate to reduce the expression of proinflammatory mediators was evaluated in cultured bovine mammary endothelial cells (BMEC) stimulated with endotoxin. Treatment of endotoxin-stimulated BMEC with ethyl pyruvate significantly reduced gene expression of IL-6, IL-8, and intercellular adhesion molecule 1 as well as expression of eicosanoid-producing enzymes, including cyclooxygenase 2 and 15-lipoxygenase 1. This is the first time that the effect of ethyl pyruvate was evaluated in an in vitro BMEC model of coliform mastitis. The ability of ethyl pyruvate to effectively inhibit gene and protein expression of potent vascular proinflammatory mediators in vitro warrants further investigations to assess in vivo efficacy. Ethyl pyruvate is safe for human consumption, and it may be an attractive candidate as a therapeutic in ameliorating the severe pathogenesis associated with coliform mastitis.

Differential leucocyte count for ewe milk with low and high somatic cell count

This study was undertaken to compare flow cytometry (FC) and direct microscopic leucocyte count (MDLC) for the differentiation of macrophages, lymphocytes and polymorphonuclear leucocyte (PMN) and to evaluate leucocyte distribution in ewe milk with low and high somatic cell count (SCC). Milk samples were grouped for somatic cell count in low SCC (LSCC) when the content was lower than 5·00 × 10(5)/ml and high SCC (HSCC) when the content was higher than 1·00 × 10(6)/ml. No differences were found between the two methods tested suggesting that FC could be used as a routine test for rapid discrimination of leucocytes. Percentages of lymphocytes in ewe milk were higher in LSCC (50%) than in HSCC (39%) and count ranged from 273·91 ± 56·62 × 10(3) cells/ml (LSCC) to 308·90 ± 46·15 × 10(3) cells/ml (HSCC). PMN number was lower in LSCC than in HSCC (248·83 ± 46·87 × 10(3) cells/ml v. 444·38 ± 58·62 × 10(3) cells/ml); accordingly the percentage was lower in LSCC (40%) than in HSCC (57%). No differences were found for macrophages which were 36·36 ± 5·51 × 10(3) cells/ml and 39·32 ± 6·83 × 10(3) cells/ml in LSCC and HSCC, respectively. Lymphocytes in ewe milk did not vary with increased number of somatic cells and were the predominant cell type in LSCC. PMN represented the main population detected in HSCC and the correlation with SCC evidenced that this leucocyte class could be useful in differentiating ewe milk cell count, being strictly responsible for the SCC increase.

Comparative kinetics of Escherichia coli- and Staphylococcus aureus-specific activation of key immune pathways in mammary epithelial cells demonstrates that S. aureus elicits a delayed response dominated by interleukin-6 (IL-6) but not by IL-1A or tumor necrosis factor alpha

Infections of the udder by Escherichia coli very often elicit acute inflammation, while Staphylococcus aureus infections tend to cause mild, subclinical inflammation and persistent infections. The molecular causes underlying the different disease patterns are poorly understood. We therefore profiled the kinetics and extents of global changes in the transcriptome of primary bovine mammary epithelial cells (MEC) after challenging them with heat-inactivated preparations of E. coli or S. aureus pathogens. E. coli swiftly and strongly induced an expression of cytokines and bactericidal factors. S. aureus elicited a retarded response and failed to quickly induce an expression of bactericidal factors. Both pathogens induced similar patterns of chemokines for cell recruitment into the udder, but E. coli stimulated their synthesis much faster and stronger. The genes that are exclusively and most strongly upregulated by E. coli may be clustered into a regulatory network with tumor necrosis factor alpha (TNF-α) and interleukin-1 (IL-1) in a central position. In contrast, the expression of these master cytokines is barely regulated by S. aureus. Both pathogens quickly trigger an enhanced expression of IL-6. This is still possible after completely abrogating MyD88-dependent Toll-like receptor (TLR) signaling in MEC. The E. coli-specific strong induction of TNF-α and IL-1 expression may be causative for the severe inflammatory symptoms of animals suffering from E. coli mastitis, while the avoidance to quickly induce the synthesis of bactericidal factors may support the persistent survival of S. aureus within the udder. We suggest that S. aureus subverts the MyD88-dependent activation of immune gene expression in MEC.

Mastitis associated transcriptomic disruptions in cattle

Mastitis is ranked as the top disease for dairy cattle based on traditional cost analysis. Greater than 100 organisms from a broad phylogenetic spectrum are able to cause bovine mastitis. Transcriptomic characterization facilitates our understanding of host-pathogen relations and provides mechanistic insight into host resistance to mastitis. In this review, we discuss effector mechanisms and transcriptomic changes within the mammary gland in response to experimental infections. We compare temporal, spatial and pathogen-specific local transcriptomic disruptions in the mammary gland as well as pathogen-induced systemic responses and transcriptional changes in distant organs. We attempt to explain why studies on transcriptomic changes during critical physiological periods and in response to non-mastitic pathogens may have important implications for mastitis studies. Future perspectives on revealing bidirectional molecular cross-talk between mastitis pathogens and host cells using cutting-edge genomic technologies are also discussed.

Assessment of epithelial cells' immune and inflammatory response to Staphylococcus aureus when exposed to a macrolide

Non-specific (innate) immune response plays a major role in defending the udder from bacterial invasion. Moreover, recent investigations suggest that mammary gland epithelial cells (MGEC) could have a large and important role as a source of soluble components of immune defences. Despite many attempts to find other ways to control/prevent mastitis (i.e. vaccine) antimicrobial therapy is still the most used and effective means of curing clinical and subclinical mastitis. However, drug concentrations and therapy durations are far from the optimal in order to reduce costs. Therefore, efficacy of antimicrobial therapy is dependent not only on the substance activity but also on the positive interactions with the host innate immune response. Surprisingly, information on these interactions is rather scarce in the mastitis field. A simple experimental model was developed based on BME-UV cell line, Staphylococcus aureus as a challenge and a macrolide as an antimicrobial to assess the interactions among epithelial cells, Staph. aureus and the potential effects of antimicrobials on the immune system. The results of this study confirmed that tylosin has good antimicrobial activity against both intracellular and extracellular Staph. aureus in bovine MGEC without affecting cell functions. In this study, a significant down-regulation of IL-1 and IL-6 was observed, while TNF and IL-8 expression rate numerically increased, but differences were not significant. To our knowledge, this is the first paper assessing the concentration of two lysosomal enzymes, lysozyme and N-acetyl-β-d-glucosaminidase (NAGase), in Staph. aureus-stimulated MGEC. The results of this study confirmed that tylosin could have a significant effect on the release of these enzymes. Moreover, even if both enzymes have a similar substrate as a target, the results suggest different secretion mechanisms and an influence of antimicrobial treatment on these mechanisms. Successful mastitis cure is the result of achieving the optimal efficiency of both innate immune defences and therapeutical activities, by means of killing bacteria without eliciting an excessive inflammatory response. Therefore, antimicrobials for mastitis therapy should be selected not only on bacterial sensitivity, but also for their positive interactions with the innate immune response of the mammary gland. This study showed that an in-vitro model based on Staph. aureus challenge on MGEC could be helpful in assessing both the intracellular and extracellular activity of antimicrobials and their influence on epithelial cell immune and inflammatory response.

Immune response of bovine milk somatic cells to endotoxin in healthy quarters with normal and very low cell counts

Low somatic cell count (SCC) is a reliable indicator of high-quality milk free of pathogenic microorganisms. Thus, an important goal in dairy practice is to produce milk with low SCC. Selection for cows with low SCC can sometimes lead to extremely low SCC in single quarters. The cells in milk are, however, predominantly immune cells with important immune functions. To investigate the mammary immune competence of quarters with very low SCC, healthy udder quarters of cows with normal SCC of (40–100)×103cells/ml and very low SCC of <20×103cells/ml were challenged with lipopolysaccharide (LPS) fromEscherichia coli. In the first experiment, SCC and cell viability after a challenge with 50 ng of LPS/quarter was investigated. In the second experiment, tumour necrosis factor α (TNF-α) concentration and lactate dehydrogenase (LDH) activity in milk, and mRNA expression of various innate immune factors in milk cells were measured after a challenge with 100 μg LPS/quarter. LPS challenge induced an increase of SCC. SCC levels reached were higher in quarters with normal SCC and maximum SCC was reached 1 h earlier than in very low SCC quarters. The increase of TNF-α concentrations in milk in response to LPS challenge was lower in quarters with very low SCC than in quarters with normal SCC. The viability of cells and the LDH activity in milk increased in response to LPS challenge, however, without a difference between the groups. The mRNA expression of IL-1β and IL-8 was increased in milk cells at 12 h after LPS challenge, whereas that of TNF-α and lactoferrin was not increased at the measured time points (12, 24 and 36 h after LPS challenge). No differences of mRNA expression of measured immune factors between normal and very low SCC samples were detected. The study showed that udder quarters with very low SCC responded with a less marked increase of SCC compared with quarters with normal SCC. This difference corresponded with simultaneously lower TNF-α concentrations in milk. However, the immune competence of the cells themselves based on mRNA expression of TNF-α, IL-8, IL-1β, and lactoferrin, did not differ. The results may indicate that very low SCC can impair the immune competence of udder quarters, because the immune response in udder quarters with lower SCC is less efficient as fewer cells contribute to the production of immunoregulators.

Effect of Panax ginseng on cytokine expression in bovine mammary glands at drying off

Biological response modifiers (BRM) are agents that modify the host's response to pathogens with resultant beneficial prophylactic or therapeutic effects. The objectives of this study were to describe the immunomodulatory effects of Panax ginseng (GS) on bovine mammary glands at the end of lactation. Eight mammary quarters from six nonpregnant cows in late lactation were infused with 10mL of BRM (3mg/mL), six quarters were treated with placebo (vehicle alone) and six quarters were maintained as uninoculated controls. Milk samples were collected at different time points for detection of specific cytokines mRNA by RT-PCR and Western blotting assay. A significant increase of IL-1α, IL-1β and TNF-α mRNA expression was observed in BRM-treated compared with placebo-treated quarters at 48h post-treatment (pt) (P<0.05). A 17kDa TNF-α band expressed a sharp elevation at 24h and reduction in its level at 48h pt in BRM-treated quarters. Differences in this cytokine level between 24 and 48h pt times were significant (P<0.05). GS extract inoculation at drying off was associated with somatic cell counts increase, cytokines mRNA transcription and the presence of TNF-α in milk and can therefore exert immunomodulating effects in bovine mammary gland at drying off.

Characterisation of physiological and immunological responses in beef cows to abrupt weaning and subsequent housing

BACKGROUND

Weaning involves the permanent separation of the calf from the dam and has been shown to be stressful for both. The objectives of this study were to characterise the effect of i) abrupt weaning and ii) subsequent housing on the extended physiological and immunological responses of beef cows. At weaning (day (d) 0, mean age of calf (s.d.) 212 (24.5) d), cows were abruptly separated from their calves and returned to the grazing area. After 35 d at pasture, cows were housed in a slatted floor shed and offered grass silage ad libitum plus a mineral-vitamin supplement daily. Rectal body temperature was recorded and blood samples were obtained on i) d 0 (weaning), 2, 7, 14, 21, 28, 35 and subsequently on ii) d 0 (housing), 2, 7, 14 and 21 for physiological, haematological and immunological measurements.

RESULTS

Post-weaning, concentration of cortisol and dehydroepiandrosterone were unchanged (P > 0.05). Rectal body temperature, neutrophil number and neutrophil: lymphocyte ratio increased (P < 0.01) on d 2 compared with pre-weaning baseline. Lymphocyte and neutrophil number decreased (P < 0.05) on d 2 to 7 and d 7 to 21, respectively, compared with pre-weaning baseline. Interferon-gamma production decreased (P < 0.05) on d 2 compared with pre-weaning baseline. An increase (P < 0.05) in acute phase proteins, fibrinogen and haptoglobin was evident on d 2 to 35 compared with pre-weaning baseline. Concentration of glucose increased on d 2 to 28, whereas non-esterified fatty acid decreased on d 2 to 35 compared with pre-weaning baseline. Post-housing, concentrations of cortisol, rectal body temperature, total leukocyte number, and glucose were unchanged (P > 0.05). On d 2 post-housing, neutrophil number and neutrophil: lymphocyte ratio increased (P < 0.05), whereas lymphocyte number and concentrations of dehydroepiandrosterone, fibrinogen and non-esterified fatty acid decreased (P < 0.05) compared with pre-housing baseline. Concentration of haptoglobin increased (P < 0.05) on d 14 to 21 post-housing.

CONCLUSIONS

A transitory increase in neutrophil number and decrease in lymphocyte number, increased neutrophil:lymphocyte ratio coupled with decreased interferon-gamma production, and increased concentration of acute phase proteins indicate a stress response in cows post-weaning, whereas post-housing, changes were less marked.

Analysis of key molecules of the innate immune system in mammary epithelial cells isolated from marker-assisted and conventionally selected cattle

Mastitis is the most prevalent infectious disease in dairy herds. Breeding programs considering mastitis susceptibility were adopted as approaches to improve udder health status. In recent decades, conventional selection criteria based on phenotypic characteristics such as somatic cell score in milk have been widely used to select animals. Recently, approaches to incorporate molecular information have become feasible because of the detection of quantitative trait loci (QTL) affecting mastitis resistance. The aims of the study were to explore molecular mechanisms underlying mastitis resistance and the genetic mechanisms underlying a QTL on Bos taurus chromosome 18 found to influence udder health. Primary cell cultures of mammary epithelial cells from heifers that were selected for high or low susceptibility to mastitis were established. Selection based on estimated pedigree breeding value or on the basis of marker-assisted selection using QTL information was implemented. The mRNA expression of 10 key molecules of the innate immune system was measured using quantitative real-time PCR after 1, 6, and 24 h of challenge with heat-inactivated mastitis pathogens (Escherichia coli and Staphylococcus aureus) and expression levels in the high and low susceptibility groups were compared according to selection criteria. In the marker-assisted selection groups, mRNA expression in cells isolated from less-susceptible animals was significantly elevated for toll-like receptor 2, tumor necrosis factor-alpha, IL-1beta, IL-6, IL-8, RANTES (regulated upon activation, normal t-cell expressed and secreted), complement factor C3, and lactoferrin. In the estimated pedigree breeding value groups, mRNA expression was significantly elevated only for V-rel reticuloendotheliosis viral oncogene homolog A, IL-1 beta, and RANTES. These observations provide first insights into genetically determined divergent reactions to pathogens in the bovine mammary gland and indicate that the application of QTL information could be a successful tool for the selection of animals resistant to mastitis.

Gene network and pathway analysis of bovine mammary tissue challenged with Streptococcus uberis reveals induction of cell proliferation and inhibition of PPARgamma signaling as potential mechanism for the negative relationships between immune response and lipid metabolism

BACKGROUND

Information generated via microarrays might uncover interactions between the mammary gland and Streptococcus uberis (S. uberis) that could help identify control measures for the prevention and spread of S. uberis mastitis, as well as improve overall animal health and welfare, and decrease economic losses to dairy farmers. The main objective of this study was to determine the most affected gene networks and pathways in mammary tissue in response to an intramammary infection (IMI) with S. uberis and relate these with other physiological measurements associated with immune and/or metabolic responses to mastitis challenge with S. uberis O140J.

RESULTS

Streptococcus uberis IMI resulted in 2,102 (1,939 annotated) differentially expressed genes (DEG). Within this set of DEG, we uncovered 20 significantly enriched canonical pathways (with 20 to 61 genes each), the majority of which were signaling pathways. Among the most inhibited were LXR/RXR Signaling and PPARalpha/RXRalpha Signaling. Pathways activated by IMI were IL-10 Signaling and IL-6 Signaling which likely reflected counter mechanisms of mammary tissue to respond to infection. Of the 2,102 DEG, 1,082 were up-regulated during IMI and were primarily involved with the immune response, e.g., IL6, TNF, IL8, IL10, SELL, LYZ, and SAA3. Genes down-regulated (1,020) included those associated with milk fat synthesis, e.g., LPIN1, LPL, CD36, and BTN1A1. Network analysis of DEG indicated that TNF had positive relationships with genes involved with immune system function (e.g., CD14, IL8, IL1B, and TLR2) and negative relationships with genes involved with lipid metabolism (e.g., GPAM, SCD, FABP4, CD36, and LPL) and antioxidant activity (SOD1).

CONCLUSION

Results provided novel information into the early signaling and metabolic pathways in mammary tissue that are associated with the innate immune response to S. uberis infection. Our study indicated that IMI challenge with S. uberis (strain O140J) elicited a strong transcriptomic response, leading to potent activation of pro-inflammatory pathways that were associated with a marked inhibition of lipid synthesis, stress-activated kinase signaling cascades, and PPAR signaling (most likely PPARgamma). This latter effect may provide a mechanistic explanation for the inverse relationship between immune response and milk fat synthesis.

Stimulated expression of TNF-alpha and IL-8, but not of lingual antimicrobial peptide reflects the concentration of pathogens contacting bovine mammary epithelial cells

We examined if and how mammary epithelial cells (MECs) calibrate and confine the intensity of an inflammatory response elicited by different concentrations of mastitis pathogens. Therefore we quantified in primary bovine MEC the effect of different E. coli pathogen concentrations upon the abundance of mRNA molecules encoding factors of immune defence. Induced synthesis of the mRNAs encoding tumor necrosis factor alpha and interleukin 8 both clearly correlated with the E. coli dose 1h after stimulation. Also the decay rate of those mRNAs reflected the pathogen load. The higher the concentration of E. coli, the faster and stronger was the up regulation and also the subsequent degradation of those particular mRNA species. Modulation of the mRNA concentration of tristetraprolin, a factor crucially involved in the mRNA degradation, followed the same pattern. In contrast, extent and kinetics of increasing the mRNA concentrations of serum amyloid A3 and lingual antimicrobial peptide were almost independent of the pathogen dose. We show that MEC perceive the information about the different pathogen concentrations and convert this signal into a calibrated synthesis of pro-inflammatory cytokines. We suggest that selective degradation of the mRNA molecules encoding those inflammatory cytokines contributes significantly to prevent an overshooting immune response in the udder.

Terminal differentiation of goat mammary tissue during pregnancy requires the expression of genes involved in immune functions

Terminal differentiation of mammary tissue into a functional epithelium that synthesizes and secretes milk occurs during pregnancy. The molecular mechanisms underlying this complex process are poorly understood, especially in ruminants. To obtain an overview of the ruminant mammary gland's final differentiation process, we conducted time-course gene expression analysis of five physiological stages: four during pregnancy (P46, P70, P90, and P110) and one after 40 days of lactation (L40). An appropriate loop experimental design was used to follow gene expression profiles. Using three nulliparous (pregnancy) or primiparous (lactation) goats per stage, we performed a comparison starting from nine dye-swaps and using a 22K bovine oligoarray. Statistical analysis revealed that the expression of 1,696 genes varied significantly at least once in the study. These genes fell into 19 clusters based on their expression profiles. Identification of biological functions with Ingenuity Pathway Analysis software revealed several similarities, in keeping with physiological stages described in mice. As in mice, expression of milk protein genes began at midpregnancy, and genes regulating lipid biosynthesis were induced at the onset of lactation. During the first half of pregnancy, the molecular signature of goat mammary tissue was characterized by the expression of genes associated with tissue remodeling and differentiation, while the second half was mainly characterized by the presence of messengers encoding genes involved in cell proliferation. A large number of immune-related genes were also induced, supporting recent speculation that mammary tissue has an original immune function, and the recruitment of migrating hematopoietic cells possibly involved in the branching morphogenesis of the mammary gland. These data hint that the induction of differentiation occurs early in pregnancy, very likely before P46. This period is therefore crucial for obtaining a healthy and productive mammary gland.

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

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.

Osteopontin: an early innate immune marker of Escherichia coli mastitis harbors genetic polymorphisms with possible links with resistance to mastitis

Background

Mastitis is the most important disease in dairy cows and it causes significant lost of profit to producers. Identification of the genes, and their variants, involved in innate immune responses is essential for the understanding of this inflammatory disease and to identify potential genetic markers for resistance to mastitis. The progeny of dairy cows would benefit from receiving favourable alleles that support greater resistance to infection, thus reducing antibiotic use. This study aims to identify a key gene in the innate immune response to mastitis, led us to evaluate its genetic association with somatic cell score (SCS), which is an indicator of clinical mastitis, and to evaluate its impact on other traits related to milk production.

Results

The osteopontin transcript (SPP1) was identified in the somatic cells from cows experimentally infected with Escherichia coli. By selecting bulls with extreme estimated breeding values (EBVs) for SCS, which is an indicator of mammary gland health, four DNA polymorphisms in the SPP1 genomic sequence were found. Statistical analysis revealed that the SNP SPP1c.-1301G>A has an impact on EBV for SCS (P < 0.001) Using an allele substitution model, SPP1c.-1251C>T, SPP1c.-430G>A, and SPP1c.*40A>C have an impact on SCS whereas SPP1c.-1301G>A has an effect on the EBVs for milk yield (second and third lactations), fat and protein percentages (all three lactations). Analysis revealed statistically significant differences between haplotype groups at a comparison-wise level with sire EBVS for SCS for the first (P = 0.012), second (P < 0.001), and third (P < 0.001) lactations.

Conclusion

This study reports the link between DNA polymorphisms of SPP1, the number of milk immune cells and, potentially, the susceptibility to mastitis. These SNPs were identified by in silico search to be located in transcription factor recognition sites which factors are presumably involved in the Th1 immune response and in the Th2 regulation pathway. Indeed, one SNP abolished the SP1 recognition site, whereas another SNP affected the transcription binding factor IKAROS. All together, these findings support the genetic potential of these variants in terms of selection for the improvement of mastitis resistance in dairy cows.

A sentinel function for teat tissues in dairy cows: dominant innate immune response elements define early response to E. coli mastitis

Escherichia coli intramammary infection elicits localized and systemic responses, some of which have been characterized in mammary secretory tissue. Our objective was to characterize gene expression patterns that become activated in different regions of the mammary gland during the acute phase of experimentally induced E. coli mastitis. Tissues evaluated were from Fürstenburg's rosette, teat cistern (TC), gland cistern (GC), and lobulo-alveolar (LA) regions of control and infected mammary glands, 12 and 24 h after bacterial (or control) infusions. The main networks activated by E. coli infection pertained to immune and inflammatory response, with marked induction of genes encoding proteins that function in chemotaxis and leukocyte activation and signaling. Genomic response at 12 h post-infection was greatest in tissues of the TC and GC. Only at 24 h post-infection did tissue from the LA region respond, at which time the response was the greatest of all regions. Similar genetic networks were impacted in all regions during early phases of intramammary infection, although regional differences throughout the gland were noted. Data support an important sentinel function for the teat, as these tissues responded rapidly and intensely, with production of cytokines and antimicrobial peptides.

Mastitis detection: current trends and future perspectives

Bovine mastitis, the most significant disease of dairy herds, has huge effects on farm economics due to reduction in milk production and treatment costs. Traditionally, methods of detection have included estimation of somatic cell counts, an indication of inflammation, measurement of biomarkers associated with the onset of the disease (e.g. the enzymes N-acetyl-beta-D-glucosaminidase and lactate dehydrogenase) and identification of the causative microorganisms, which often involves culturing methods. These methods have their limitations and there is a need for new rapid, sensitive and reliable assays. Recently, significant advances in the identification of nucleic acid markers and other novel biomarkers and the development of sensor-based platforms have taken place. These novel strategies have shown promise, and their advantages over the conventional tests are discussed.

Metabolic factors affecting the inflammatory response of periparturient dairy cows

Dairy cattle are susceptible to increased incidence and severity of disease during the periparturient period. Increased health disorders have been associated with alterations in bovine immune mechanisms. Many different aspects of the bovine immune system change during the periparturient period, but uncontrolled inflammation is a dominant factor in several economically important disorders such as metritis and mastitis. In human medicine, the metabolic syndrome is known to trigger several key events that can initiate and promote uncontrolled systemic inflammation. Altered lipid metabolism, increased circulating concentrations of non-esterified fatty acids and oxidative stress are significant contributing factors to systemic inflammation and the development of inflammatory-based diseases in humans. Dairy cows undergo similar metabolic adaptations during the onset of lactation, and it was postulated that some of these physiological events may negatively impact the magnitude and duration of inflammation. This review will discuss how certain types of fatty acids may promote uncontrolled inflammation either directly or through metabolism into potent lipid mediators. The relationship of increased lipid metabolism and oxidative stress to inflammatory dysfunction will be reviewed as well. Understanding more about the underlying cause of periparturient health disorders may facilitate the design of nutritional regimens that will meet the energy requirements of cows during early lactation and reduce the susceptibility to disease as a function of compromised inflammatory responses.

The acute-phase protein serum amyloid A3 is expressed in the bovine mammary gland and plays a role in host defence

The serum amyloid A protein is one of the major reactants in the acute-phase response. Using representational difference analysis comparing RNA from normal and involuting quarters of a dairy cow mammary gland, we found an mRNA encoding the SAA3 protein (M-SAA3). The M-SAA3 mRNA was localized to restricted populations of bovine mammary epithelial cells (MECs). It was expressed at a moderate level in late pregnancy, at a low level through lactation, was induced early in milk stasis, and expressed at high levels in most MECs during mid to late involution and inflammation/mastitis. The mature M-SAA3 peptide was expressed in Escherichia coli, antibodies made, and shown to have antibacterial activity against E. coli, Streptococcus uberis and Pseudomonas aeruginosa. These results suggest that the mammary SAA3 may have a role in protection of the mammary gland during remodelling and infection and possibly in the neonate gastrointestinal tract.

Cell population, viability, and some key immunomodulatory molecules in different milk somatic cell samples in dairy cows

Immune cells in the milk are most important in combating pathogens that invade the mammary gland. This study investigated the immune competence and viability of somatic milk cells that are already resident in milk and udders free of infection. Cells were studied in freshly removed milk to simulate conditions in the udder. Effects of incubation, cell preparation, and immunological stimulation with 0·5 μg/ml lipopolysaccharide (LPS) fromEscherichia coliwere analysed. Viability and differential counts of milk cells between high and low somatic cell count (SCC) quarters, and cisternal and alveolar milk with and without LPS stimulation were compared. Incubation and preparation of cells caused a cell loss which further increased with time independently of SCC and milk fraction. The viability of these cells was stable until 3 h post incubation and decreased until 6 h. Cell populations differed between both investigations, but did not change during the course of the experiment. mRNA expression of immune and apoptosis factors of the cells, measured by qPCR, did not change substantially: mRNA expression of caspase 3, Toll like receptor 4, and GM-CSF did not change, whereas the expression of the death receptor Fas/APO-1 (CD95), lactoferrin and lysozyme was decreased at 6 h. Cyclooxygenase-2 and TNF-α mRNA expression were decreased after 6 h of LPS treatment. In comparison with other studies in vivo or in vitro (in cell culture), in this study where cells are studied ex vivo (removed from the udder but kept in their natural environment, the milk) resident milk cells seem to be more vulnerable, less viable, less able to respond to stimulation, and thus less immune competent compared with cells that have freshly migrated from blood into milk after pathogen stimulation. The cell viability and differential cell count differed between high- and low-SCC milk and between cisternal and alveolar milk depending on the individual cow. In conclusion, the results support the view that for a most effective defence against invading pathogens the mammary gland is reliant on the recruitment of fresh immune cells from the blood.

Changing trends in mastitis

The global dairy industry, the predominant pathogens causing mastitis, our understanding of mastitis pathogens and the host response to intramammary infection are changing rapidly. This paper aims to discuss changes in each of these aspects. Globalisation, energy demands, human population growth and climate change all affect the dairy industry. In many western countries, control programs for contagious mastitis have been in place for decades, resulting in a decrease in occurrence of Streptococcus agalactiae and Staphylococcus aureus mastitis and an increase in the relative impact of Streptococcus uberis and Escherichia coli mastitis. In some countries, Klebsiella spp. or Streptococcus dysgalactiae are appearing as important causes of mastitis. Differences between countries in legislation, veterinary and laboratory services and farmers' management practices affect the distribution and impact of mastitis pathogens. For pathogens that have traditionally been categorised as contagious, strain adaptation to human and bovine hosts has been recognised. For pathogens that are often categorised as environmental, strains causing transient and chronic infections are distinguished. The genetic basis underlying host adaptation and mechanisms of infection is being unravelled. Genomic information on pathogens and their hosts and improved knowledge of the host's innate and acquired immune responses to intramammary infections provide opportunities to expand our understanding of bovine mastitis. These developments will undoubtedly contribute to novel approaches to mastitis diagnostics and control.