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

Cows with diverging haplotypes show differences in differential milk cell count, milk parameters and vaginal temperature after S. aureus challenge but not after E. coli challenge

BACKGROUND

In dairy cattle, mastitis causes high financial losses and impairs animal well-being. Genetic selection is used to breed cows with reduced mastitis susceptibility. Techniques such as milk cell flow cytometry may improve early mastitis diagnosis. In a highly standardized in vivo infection model, 36 half-sib cows were selected for divergent paternal Bos taurus chromosome 18 haplotypes (Q vs. q) and challenged with Escherichia coli for 24 h or Staphylococcus aureus for 96 h, after which the samples were analyzed at 12 h intervals. Vaginal temperature (VT) was recorded every three minutes. The objective of this study was to compare the differential milk cell count (DMCC), milk parameters (fat %, protein %, lactose %, pH) and VT between favorable (Q) and unfavorable (q) haplotype cows using Bayesian models to evaluate their potential as improved early indicators of differential susceptibility to mastitis.

RESULTS

After S. aureus challenge, compared to the Q half-sibship cows, the milk of the q cows exhibited higher PMN levels according to the DMCC (24 h, p < 0.001), a higher SCC (24 h, p < 0.01 and 36 h, p < 0.05), large cells (24 h, p < 0.05) and more dead (36 h, p < 0.001) and live cells (24 h, p < 0.01). The protein % was greater in Q milk than in q milk at 0 h (p = 0.025). In the S. aureus group, Q cows had a greater protein % (60 h, p = 0.048) and fat % (84 h, p = 0.022) than q cows. Initially, the greater VT of S. aureus-challenged q cows (0 and 12-24 h, p < 0.05) reversed to a lower VT in q cows than in Q cows (48-60 h, p < 0.05). Additionally, the following findings emphasized the validity of the model: in the S. aureus group all DMCC subpopulations (24 h-96 h, p < 0.001) and in the E. coli group nearly all DMCC subpopulations (12 h-24 h, p < 0.001) were higher in challenged quarters than in unchallenged quarters. The lactose % was lower in the milk samples of E. coli-challenged quarters than in those of S. aureus-challenged quarters (24 h, p < 0.001). Between 12 and 18 h, the VT was greater in cows challenged with E. coli than in those challenged with S. aureus (3-h interval approach, p < 0.001).

CONCLUSION

This in vivo infection model confirmed specific differences between Q and q cows with respect to the DMCC, milk component analysis results and VT results after S. aureus inoculation but not after E. coli challenge. However, compared with conventional milk cell analysis monitoring, e.g., the global SCC, the DMCC analysis did not provide refined phenotyping of the pathogen response.

Milk miRNA expression in buffaloes as a potential biomarker for mastitis

BACKGROUND

Buffaloes have the highest potential for production due to a promising gene pool that is being enhanced and upgraded. Mastitis is a significant health impediment that greatly diminishes milk yield and quality, affecting rural farmers' livelihoods. The traditional gold standard used for diagnosing mastitis or subclinical mastitis is CMT, but it has the drawback of false positive or negative results. Subclinical mastitis, if not treated promptly, can lead to mammary tumors. To address the gap in early diagnosis of subclinical mastitis in CMT-negative milk of buffaloes, we performed a retrospective analysis and evaluated the milk miRNA expression profiles as potential biomarkers.

RESULTS

Thirty buffalo milk samples based on clinical signs and CMT were divided into normal, subclinical, and clinical mastitis. SCC evaluation showed significant differences between the groups. The data analysis demonstrated that the elevation of miR-146a and miR-383 differed substantially between normal, subclinical, and clinical mastitis milk of buffaloes with 100% sensitivity and specificity. The relationship of SCC with miR-146a and miR-383 in normal/healthy and subclinical mastitis was positively correlated.

CONCLUSION

The overexpression of miR-146a and miR-383 is associated with inflammation. It can be a valuable prognostic and most sensitive biomarker for early mastitis detection in buffaloes with SCC below 2 lakhs and CMT-ve, enhancing the accuracy of subclinical mastitis diagnosis.

Cytokine inflammatory response in dairy cows with mastitis caused by Streptococcus agalactiae

Introduction

The aim of the study was evaluation of the concentrations of interleukin (IL)-1β, IL-8, IL-12β and tumour necrosis factor alpha (TNF-α) in the serum and milk of cows with mastitis caused by Streptococcus agalactiae.

Material and Methods

A total of 60 milk samples from diseased cows and 30 milk samples from healthy cows were included in the study. Blood and milk samples were taken from Holstein-Friesian cows from three herds (two in tie-stall and one in a free-stall housing system) in Lublin Province in Poland. The concentrations of cytokines in blood serum and quarter milk samples were determined by ELISA.

Results

The levels of IL-1β, IL-8, IL-12β and TNF-α were significantly higher in the milk of cows suffering from mastitis caused by S. agalactiae compared to the milk of healthy cows (263.03 vs 55.36 pg/mL, 298.34 vs 131.82 pg/mL, 604.10 vs 139.17 pg/mL and 460.86 vs 78.82 pg/mL, respectively). In the group of sick cows, cytokine levels were significantly higher in milk than in serum (263.03 vs 55.25 pg/mL for IL-1β, 298.34 vs 164.22 pg/mL for IL-8, 604.10 vs 70.34 pg/mL for IL-12β and 460.86 vs 104.78 pg/mL for TNF-α).

Conclusion

The results confirm the involvement of the entire bovine immune system to protect against the bacteria first locally in the udder. The response of the mammary gland to infection caused by S. agalactiae is rapid and already very strong at the beginning of the infection.

Identification of hub genes associated with somatic cell score in dairy cow

CONTEXT

Somatic cell count (SCC) is used as an indicator of udder health. The log transformation of SCC is called somatic cell score (SCS).

AIM

Several QTL and genes have been identified that are associated with SCS. This study aimed to identify the most important genes associated with SCS.

METHODS

This study compiled 168 genes that were reported to be significantly linked to SCS. Pathway analysis and network analysis were used to identify hub genes.

KEY RESULTS

Pathway analysis of these genes identified 73 gene ontology (GO) terms associated with SCS. These GO terms are associated with molecular function, biological processes, and cellular components, and the identified pathways are directly or indirectly linked with the immune system. In this study, a gene network was constructed, and from this network, the 17 hub genes (CD4, CXCL8, TLR4, STAT1, TLR2, CXCL9, CCR2, IGF1, LEP, SPP1, GH1, GHR, VWF, TNFSF11, IL10RA, NOD2, and PDGFRB) associated to SCS were identified. The subnetwork analysis yielded 10 clusters, with cluster 1 containing all identified hub genes (except for the VWF gene).

CONCLUSION

Most hub genes and pathways identified in our study were mainly involved in inflammatory and cytokine responses.

IMPLICATIONS

Result obtained in current study provides knowledge of the genetic basis and biological mechanisms controlling SCS. Therefore, the identified hub genes may be regarded as the main gene for the genomic selection of mastitis resistance.

Syndecan-3 Coregulates Milk Fat Metabolism and Inflammatory Reactions in Bovine Mammary Epithelial Cells through AMPK/SIRT1 Signaling Pathway

Transcriptome sequencing showed that syndecan-3 (SDC3) was differentially expressed in high-fat and low-fat mammary epithelial cells of Chinese Holstein cows. Previous studies found that SDC3 plays an important role in inflammatory diseases and virus infection. However, those studies did not confirm whether or not the functional gene SDC3, which plays an important role in regulating milk fat metabolism, has an effect on susceptibility to breast tissue diseases. Therefore, we studied the effects of SDC3 on milk lipid metabolism and inflammation in bovine mammary epithelial cells (BMECs) and further explored the common regulatory pathway of SDC3 in both. The overexpression of SDC3 increased the contents of triglycerides and cholesterol, reduced the content of non-esterified fatty acids, inhibited the expression of inflammatory factors (IL-6, IL-1β, TNF-α and COX-2), and reduced the production of ROS in BMECs. However, silenced SDC3 had the opposite effect. Further exploring the mechanisms of SDC3, we found that SDC3 upregulated the expression of peroxisome proliferator-activated receptor gamma (PPARG) through the AMPK/SIRT1 signal pathway to promote milk fat synthesis. It also regulated the activation of the NF-κB pathway through the AMPK/SIRT1 signal pathway, reducing the expression of inflammatory factors and ROS production, thus inhibiting the inflammatory response of BMECs. Nuclear factor kappa B subunit 1 (NF-κB p50) was an important target of SDC3 in this process. To sum up, our results showed that SDC3 coregulated milk fat metabolism and inflammation through the AMPK/SIRT1 signaling pathway. This study laid a foundation for the comprehensive evaluation of breeding value based on multi-effect functional genes in dairy cow molecular breeding.

Mastitis: Impact of Dry Period, Pathogens, and Immune Responses on Etiopathogenesis of Disease and its Association with Periparturient Diseases

Mastitis is an inflammation of the mammary gland initiated by pathogenic bacteria. In fact, mastitis is the second most important reason for the culling of cows from dairy herds, after infertility. In this review we focus on various forms of mastitis, including subclinical and clinical mastitis. We also stress the importance of the dry-off period as an important time when pathogenic bacteria might start their insult to the mammary gland. An important part of the review is the negative effects of mastitis on milk production and composition, as well as economic consequences for dairy farms. The two most important groups of bacteria that are involved in infection of the udder, Gram-negative and Gram-positive bacteria, are also discussed. Although all cows have both innate and adaptive immunity against most pathogens, some are more susceptible to the disease than others. That is why we summarize the most important components of innate and adaptive immunity so that the reader understands the specific immune responses of the udder to pathogenic bacteria. One of the most important sections of this review is interrelationship of mastitis with other diseases, especially retained placenta, metritis and endometritis, ketosis, and laminitis. Is mastitis the cause or the consequence of this disease? Finally, the review concludes with treatment and preventive approaches to mastitis.

Differential immune response to two Staphylococcus aureus strains with distinct adaptation genotypes after experimental intramammary infection of dairy cows

The aim of this study was to evaluate and compare the ability of two S. aureus strains with different adaptation genotypes (low and high) to the bovine mammary gland (MG) to establish an intramammary infection (IMI) and induce an immune response after an experimental challenge in lactating cows. Two isolates (designated 806 and 5011) from bovine IMI with different genotypic profiles, harboring genes involved in adherence and biofilm production, belonging to different capsular polysaccharide (CP) type, accessory gene regulator (agr) group, pulsotype (PT) and sequence type/clonal complex (ST/CC) were selected. Strains 806 and 5011 were associated with low (nonpersistent-NP) and high (persistent-P) adaptation to the MG, respectively. Strain 806 (NP) was characterized as agr group II, cap5 positive and ST350; strain 5011 (P) agr group I, cap8 positive and CC188. Three groups of clinically healthy cows, 4 cows/treatment group, were inoculated by the intramammary route with strain 806 (NP), strain 5011 (P) and pyrogen-free saline solution. All mammary quarters challenged with strain 806 (NP) developed mild clinical mastitis between 1 and 7 d post inoculation (pi). Quarters challenged with strain 5011 (P) developed a persistent IMI; bacteria were recovered from milk from d 7 pi and up to d 56 pi. In quarters inoculated with strain 806 (NP) the inflammatory response induced was greater and earlier than the one induced by strain 5011 (P), since a somatic cell count (SCC) peak was observed at d 2 pi, while in quarters inoculated with strain 5011 (P) no variations in SCC were observed until d 4 pi reaching the maximum values at d 14 pi; indicating a lower and delayed initial inflammatory response. The highest levels of nitric oxide (NO) and lactoferrin (Lf) detected in milk from quarters inoculated with both S. aureus strains coincided with the highest SCC at the same time periods, indicating an association with the magnitude of inflammation. The high levels of IL-1β induced by strain 806 (NP) were associated with the highest SCC detected (d 2 pi); while quarters inoculated with strain 5011 (P) showed similar IL-1β levels to those found in control quarters. In quarters inoculated with strain 806 (NP) two peaks of IL-6 levels on d 2 and 14 pi were observed; while in quarters inoculated with strain 5011 (P) IL-6 levels were similar to those found in control quarters. The strain 806 (NP) induced a higher total IgG and IgG₁ response; while strain 5011 (P) generated a higher IgG₂ response (even against the heterologous strain). The present study demonstrated that S. aureus strains with different genotype and adaptability to bovine MG influence the local host immune response and the course and severity of the infectious process.

Integrated Analysis of Transcriptome mRNA and miRNA Profiles Reveals Self-Protective Mechanism of Bovine MECs Induced by LPS

Many studies have investigated the molecular crosstalk between mastitis-pathogens and cows by either miRNA or mRNA profiles. Here, we employed both miRNA and mRNA profiles to understand the mechanisms of the response of bovine mammary epithelial cells (bMECs) to lipopolysaccharide (LPS) by RNA-Seq. The total expression level of miRNAs increased while mRNAs reduced after LPS treatment. About 41 differentially expressed mRNAs and 45 differentially expressed miRNAs involved in inflammation were screened out. We found the NFκB-dependent chemokine, CXCL1, CXCL3, CXCL6, IL8, and CX3CL1 to be strongly induced. The anti-apoptosis was active because BCL2A1 and BIRC3 significantly increased with a higher expression. The effects of anti-microbe and inflammation were weakly activated because TNF, IL1, CCL20, CFB, S100A, MMP9, and NOS2A significantly increased but with a low expression, IL6 and β-defensin decreased. These activities were supervised by the NFKBIA to avoid excessive damage to bMECs. The bta-let-7a-5p, bta-miR-30a-5p, bta-miR-125b, and bta-miR-100 were essential to regulate infection process in bMECs after LPS induction. Moreover, the lactation potential of bMECs was undermined due to significantly downregulated SOSTDC1, WNT7B, MSX1, and bta-miR-2425-5p. In summary, bMECs may not be good at going head-to-head with the pathogens; they seem to be mainly charged with sending out signals for help and anti-apoptosis for maintaining lives after LPS induction.

Inflammatory Response of Primary Cultured Bovine Mammary Epithelial Cells to Staphylococcus aureus Extracellular Vesicles

Simple Summary

Mastitis, the inflammation of the mammary gland, is one of the most common and costly diseases worldwide, and Staphylococcus aureus (S. aureus) is among the most prevalent microorganisms that cause it. To obtain new insights into S. aureus mammary gland infections, we have isolated S. aureus extracellular vesicles to challenge in vitro primary bovine mammary epithelial cells. Despite the toxic content of the vesicles, we observed only a minor pro-inflammatory response. The latter can contribute to the explanation of how S. aureus evades mammary epithelial defence mechanisms and successfully colonizes the mammary gland.

Abstract

In dairy cows, Staphylococcus aureus (S. aureus) is among the most prevalent microorganisms worldwide, causing mastitis, an inflammation of the mammary gland. Production of extracellular vesicles (EVs) is a common feature of S. aureus strains, which contributes to its pathogenesis by delivering bacterial effector molecules to host cells. In the current study, we evaluated the differences between five S. aureus mastitis isolates regarding their EV production. We found that different mastitis-related S. aureus strains differ in their behaviour of shedding EVs, with M5512VL producing the largest amount of EVs containing alpha-haemolysin, a strong cytotoxic agent. We stimulated primary cultured bovine mammary epithelial cells (pbMECs) with EVs from the S. aureus strain M5512VL. After 24 h of incubation, we observed a moderate increase in gene expression of tumour necrosis factor-alpha (TNF-α) but, surprisingly, a lack of an associated pronounced pro-inflammatory response. Our results contribute to understanding the damaging nature of S. aureus in its capacity to effectively affect mammary epithelial cells.

Metformin Inhibits Lipoteichoic Acid-Induced Oxidative Stress and Inflammation Through AMPK/NRF2/NF-κB Signaling Pathway in Bovine Mammary Epithelial Cells

The objective of this research was to explore the effect of metformin on the lipoteichoic acid (LTA)–induced mastitis model using isolated primary bovine mammary epithelial cells (PBMECs). The PBMECs were exposed to either 3 mM metformin for 12 h as a metformin group (MET) or 100 μg/mL LTA for 6 h as LTA group (LTA). Cells pretreated with 3 mM metformin for 12 h followed by washing and 100 μg/mL LTA exposure for 6 h served as the MET + LTA group. Phosphate-buffered saline was added to cells as the control group. PBMECs pretreated with different metformin doses were analyzed by a flow cytometry (annexin V–fluorescein isothiocyanate assay) to detect the cell apoptotic rate. We performed quantitative reverse transcriptase–polymerase chain reaction and Western blot analysis to evaluate the inflammatory and oxidative responses to metformin and LTA by measuring cellular cytotoxicity, mRNA expression, and protein expression. Immunofluorescence was used to evaluate nuclear localization. The results showed that the gene expression of COX2, IL-1β, and IL-6 significantly increased in the cells challenged with LTA doses compared to control cells. In inflammatory PBMECs, metformin attenuated LTA-induced expression of inflammatory genes nuclear factor κB (NF-κB) p65, tumor necrosis factor α, cyclooxygenase 2, and interleukin 1β, as well as the nuclear localization and phosphorylation of NF-κBp65 protein, but increased the transcription of nuclear factor erythroid 2–related factor 2 (Nrf2) and Nrf2-targeted antioxidative genes heme oxygenase-1 (HO-1) and Gpx1, as well as the nuclear localization of HO-1 protein. Importantly, metformin-induced activation of Nrf2 is AMP-activated protein kinase (AMPK)–dependent; as metformin-pretreated PBMECs activated AMPK signaling via the upregulation of phosphorylated AMPK levels, cell pretreatment with metformin also reversed the translocation of Nrf2 that was LTA inhibited. This convergence between AMPK and Nrf2 pathways is essential for the anti-inflammatory effect of metformin in LTA-stimulated PBMECs. Altogether, our results indicate that metformin exerts anti-inflammation and oxidative stress through regulation of AMPK/Nrf2/NF-κB signaling pathway, which highlights the role of AMPK as a potential therapeutic strategy for treatment of bovine mastitis.

The effect of staphylococcal mastitis including resistant strains on serum procalcitonin, neopterin, acute phase response and stress biomarkers in Holstein dairy cows

Staphylococcal mastitis (SM) is a frequent disease in the dairy cattle that is costly to treat. This study aimed to investigate the alterations in the levels of procalcitonin (PCT), neopterin (NPT), haptoglobin (HP), serum amyloid A (SAA), proinflammatory cytokines (IL-1β, IL-8, TNF-α, IF-γ) and oxidative stress (OS) biomarkers in Holstein dairy cows with SM under field conditions. In addition, we also evaluated the role of examined biomarkers in disease pathogenesis and their use as diagnostic biomarkers for the disease in dairy cows. Fifty-three dairy cows with SM, including those with infections caused by Staphylococcus aureus (n = 42) and methicillin resistant S. aureus (MRSA) (n = 11) were selected for this study. In addition, 20 healthy dairy cows were enrolled as a control group. Higher serum levels of PCT, NP, IL-1β, IL-8, TNF-α, IF-γ, HP and SAA and a state of OS was detected in SM group in comparison with the controls. Moreover, the levels of all examined biomarkers in mastitic cows with S. aureus when compared with those infected with MRSA was not significantly different. All examined biomarkers demonstrated a significant degree of discrimination between SM cows and healthy controls (the area under the curve (AUC) ranged from 83.6 for SAA to 100 for PCT). Our study showed that SM in dairy cows was associated with substantial changes in serum PCT, NPT, Acute phase proteins (APPs), proinflammatory cytokines, and OS levels. This study demonstrates that clinical examination in tandem with quantification of PCT, NPT, APPs and cytokines, OS biomarkers could be a useful assessment tool for SM in dairy cows.

1,25-hydroxyvitamin D3 decreases endoplasmic reticulum stress-induced inflammatory response in mammary epithelial cells

Recent studies indicated that intramammary administration of active vitamin D₃ hormone (1,25D₃) inhibits the inflammatory process associated with mastitis. We hypothesized that attenuation of endoplasmic reticulum (ER) stress by 1,25D₃ in mammary epithelial cells (MECs) is an important cellular mechanism contributing to this beneficial effect of intramammary treatment with 1,25D₃. To test this hypothesis, the effect of 1,25D₃ was studied on induction of ER stress in a transformed human MEC line, MCF-7 cells. Treatment with two different ER stress inducers, thapsigargin (TG) and tunicamycin (TM), caused a dose-dependent induction of ER stress as evident from up-regulation of protein kinase RNA-like ER kinase (PERK), heat shock protein family A (Hsp70) member 5 (HSPA5), activating transcription factor (ATF4), ATF6, DNA damage inducible transcript 3 (DDIT3) and spliced X-box binding protein 1 (sXBP1) and impaired cell viability and decreased expression of vitamin D receptor (VDR) in MCF-7 cells (P < 0.05). Treatment with 1,25D₃ (100 nM) inhibited TG (10 nM)- and TM (1 μg/mL)-induced mRNA and/or protein levels of ATF4, ATF6, DDIT3 and HSPA5 in MCF-7 cells (P < 0.05). In addition, 1,25D₃ (100 nM) antagonized the effect of TG (10 nM) and TM (1 μg/mL) on mRNA and protein levels of VDR and mRNA levels of genes involved in production and degradation of 1,25D₃ in MCF-7 cells (P < 0.05). Moreover, 1,25D₃ (100 nM) inhibited nuclear factor-κB (NF-κB) activation in response to TM (10 nM) and TG (1 μg/mL) in MCF-7 cells. In conclusion, the present findings show that 1,25D₃ is effective in attenuating ER stress and the NF-κB-driven inflammatory response in MCF-7 cells. This indicates that attenuation of ER stress by 1,25D₃ in MECs may contribute to the recently observed inhibitory effect of intramammary treatment of dairy cows with 1,25D₃ on the inflammatory process associated with mastitis.

Klebsiella pneumoniae isolated from bovine mastitis is cytopathogenic for bovine mammary epithelial cells

Klebsiella pneumoniae, a common cause of clinical mastitis (CM) in dairy cows, can cause severe clinical symptoms. However, its pathogenicity in the bovine mammary gland is not well understood. Our objectives were to establish an in vitro infection model of K. pneumoniae on bovine mammary epithelial cells (bMEC) to assess (1) cytopathogenicity (adhesive and invasive ability, damage and apoptosis, pro-inflammatory effects) of K. pneumoniae on bMEC and (2) the role of hypermucoviscous (HMV) phenotype on cytopathogenicity. Two K. pneumoniae isolates from CM cows, 1 HMV and 1 non-HMV, were used to infect bMEC. Adhesion and invasion ability, release of lactate dehydrogenase (LDH), ultrastructural morphology, apoptosis, transcriptional expression of pro-inflammatory genes and production of pro-inflammatory cytokines were characterized at various intervals. Both K. pneumoniae isolates rapidly adhered to and invaded bMEC within 1 h post infection (pi), causing ultrastructural damage (swelling of mitochondria and vesicle formation on cell surface) after 3 h pi and apoptotic death after 9 h pi. In addition, K. pneumoniae promoted transcriptional expression of pro-inflammatory genes IL-6, IL-8, IL-1β, and tumor necrosis factor (TNF)-α and production of IL-8, IL-1β, and TNF-α cytokines. Compared with non-HMV K. pneumoniae, the HMV isolate had lower adhesive and invasive abilities but caused more serious cellular damage. In conclusion, K. pneumoniae was cytopathogenic on bMEC and induced a pro-inflammatory response; however, the HMV phenotype did not have a key role in pathogenicity. Therefore, more attention should be paid to milk loss, and targeted prevention and treatment strategies should be implemented in Klebsiella mastitis episodes.

Isolated perfused udder model for transcriptome analysis in response to Streptococcus agalactiae

This study aimed to evaluate the transcriptional changes occurring in isolated perfused mammary alveolar tissue in response to inoculation with S. agalactiae and to identify the most affected biological functions and pathways after 3 h. Four udders taken at slaughter from cows with healthy mammary gland were perfused ex situ with warmed and gassed Tyrode's solution. Mammary alveolar tissue samples were taken from the left fore and rear quarters (IQ-inoculated quarters) before inoculation (hour 0) and at 3 h post inoculation (hpi) and at the same times from control right fore and rear quarters (not inoculated: NIQ). A total of 1756 differentially expressed genes (DEGs) were identified between IQ and NIQ at 3 hpi using edgeR package. Within this set of DEGs, 952 were up regulated and mainly involved with innate immune response and inflammatory response, e.g., CD14, CCL5, TLR2, IL-8, SAA3, as well as in transcriptional regulation such as FOS, STAT3 and NFKBIA. Genes down-regulated (804) included those involved with lipid synthesis e.g., APOC2, SCD, FABP3 and FABP4. The most affected pathways were chemokine signaling, Wnt signaling and complement and coagulation cascades, which likely reflects the early stage response of mammary tissue to S. agalactiae infection. No significant gene expression changes were detected by RNA-Seq in the others contrasts. Real time-PCR confirmed the increase in mRNA abundance of immune-related genes: TLR2, TLR4, IL-1β, and IL-10 at 3 hpi between IQ and NIQ. The expression profiles of Casp1 and Bax for any contrasts were unaffected whereas Bcl2 was increased in IQ, which suggests no induction of apoptosis during the first hours after infection. Results provided novel information regarding the early functional pathways and gene network that orchestrate innate immune responses to S. agalactiae infection. This knowledge could contribute to new strategies to enhance resistance to this disease, such as genomic selection.

Amount of Milk Neutrophil Percentage and Associated CD Molecular Changes on the Compositional and Technological Properties of Milk

Background:

Changes occurring in the activity and expression of neutrophils and their transmigration through the blood mammary barrier owing to a mammary infection affecting milk quality and outcome of mastitis.

Objective:

To understand the role played by various neutrophil molecules on mastitis and milk quality.

Methods:

18 Karan Fries cows of similar parity, milk yield and lactation stage were selected and screened for mastitis based upon milk Somatic Cell Counts (SCC) as well as California mastitis test and divided into 3 groups of 6 eachi.e., healthy, sub-clinical (SCM), Clinical Mastitis (CM). Milk samples were analyzed for milk composition and technological properties. Milk neutrophils were isolated and their percentage, Phagocytic Activity (PA), viability were estimated. Activities of neutrophil enzymesi.e. Elastase 2, Collagenase and Cathepsin G were analyzed using ELISA. Relative mRNA expression of cell surface molecules like selectin (CD-62L), integrin (CD-11b), chemokine receptors (CXCR1 and CXCR2), CD-44 and chemotactic factor (IL-8) in milk neutrophil were also studied.

Results:

In the present study, neutrophil percentage (%) was significantly (p˂0.05) higher in SCM and CM milk samples compared to healthy milk samples, whereas neutrophil PA, viability were significantly (p˂0.05) lower in both samples contrast to healthy samples. Activities of Elastase 2 and Collagenase were significantly (p˂0.05) more in SCM milk. There was a significant (p˂0.05) difference in protein, pH, and lactose between healthy, SCM and SCM and CM milk. Significantly (p˂0.05) high Electrical Conductivity (EC) was observed in CM milk than SCM and CM milk. No significant changes in milk fat, Solid Not Fat (SNF) and density were found among any of the groups. The relative mRNA expression of CXCR1, CXCR2 and IL-8 were significantly (p˂0.05) high in milk neutrophils with the progression of SCM and CM, whereas significantly higher expression of CD11b CD-11b was found only in CM cows but there was no change in the expression of CD62L CD-62L in any of the groups. Expression of CD-44 molecule increased significantly in SCM cows, whereas it decreased significantly in clinically infected mastitis cows.

Conclusion:

This study highlights the changes occurring in the activity of milk neutrophils in healthy, subclinical and clinical mastitis crossbred cows.

The effect of J5 bacterins on clinical, behavioral, and antibody response following an Escherichia coli intramammary challenge in dairy cows at peak lactation

Vaccination against coliform mastitis has become part of mastitis control programs in the past 3 decades, as a means of reducing the severity of clinical mastitis. Our study objective was to evaluate the effect of 2 commercially available vaccines on clinical, behavioral, and antibody response following Escherichia coli intramammary challenge in cows near peak lactation. Cows (n = 12 per group) were vaccinated with vaccine 1 (V1) or vaccine 2 (V2) at dry-off, 21 d pre-calving, and 14 d post-calving. Twelve cows served as unvaccinated controls (CTL). Cows were challenged with E. coli in a rear quarter at approximately 100 d in milk. Milk samples were collected pre- and post-challenge to enumerate E. coli and determine somatic cell count. Serum was collected before each vaccination and at d 0, 1, 2, 3, 6, 30, and 60 relative to challenge, to study antibody response. Milk IgA and tumor necrosis factor-α concentrations were determined in whey. Vaginal temperature, cow activity, and milk yield and components were monitored post-challenge. Bacterial count, somatic cell score, milk yield and component decline, vaginal temperature, activity measures, and antibody and cytokine response were analyzed for treatment differences. The effects of parity, breed, and a repeated measure of time were also tested. Seven cows had to be removed from the study post-challenge for antibiotic treatment (CTL and V1, n = 3 each; V2, n = 1), 2 of which were euthanized (both CTL). Vaccinated cows exhibited fever (vaginal temperature ≥39.4°C) 3 h earlier than CTL cows, but we found no differences between treatments for bacterial count, somatic cell score, or milk yield reduction. Vaccinated cows spent more time lying per rest bout 2 d post-challenge, but total daily lying time was not different from CTL cows during the 7 d post-challenge. The vaccines differed in antibody response: V1 cows had greater serum IgG₁ and IgG₂ post-challenge. A parity effect was also evident: primiparous cows had lower bacterial counts, somatic cell score and a smaller milk yield decline than multiparous cows, but also had lower antibody production. Immunization with either J5 bacterin did not reduce clinical signs of mastitis in cows challenged at 100 d in milk, demonstrating that the effects of J5 vaccination had diminished at peak lactation.

Selenium ameliorates Staphylococcus aureus-induced inflammation in bovine mammary epithelial cells by inhibiting activation of TLR2, NF-κB and MAPK signaling pathways

BACKGROUND

Staphylococcus aureus (S. aureus) internalization into bovine mammary epithelial cells (bMECs) is considered an important pathogenic mechanism for the establishment of mastitis. Given the interesting link between selenium (Se) status and mastitis, our objective was to prove that Se was essential to suppress pro-inflammatory mediators, in part, by modulation of Toll-like receptor2 (TLR2), nuclear factor kappaB (NF-κB) and mitogen activated protein kinase (MAPK) signal transduction pathway in bMECs.

RESULTS

Results showed that Se (0~ 16 μM) did not affect the growth of bMECs. The mRNA expression of TLR2, Myeloid differentiation factor 88 (Myd88), Interleukin-1 receptor-associated kinase4 (Irak4), Interleukin-1 receptor-associated kinase1 (Irak1) and TNF receptor-associated factor6 (Traf6) in TLR2 signal pathway were increased or significantly increased by S. aureus. Se played an important role in regulating the genes expression of TLR2, Myd88, Traf6 but not in controlling the expression of Irak4 and Irak1. In addition, Se exerted strong inhibitory effects on the genes expression of tumor necrosis factor-alpha (TNF-α), interleukin-1β (IL-1β) and interleukin-6 (IL-6) induced by S. aureus. To further investigate the possible signaling mechanisms involved in the processes, we analyzed the role of MAPK and NF-κB signaling pathway in inflammation response in S. aureus-stimulated bMECs in vitro. Results showed that the phosphorylation of inhibitory kappaB alpha (IκBα), p65, p38 and extracellular regulated protein kinase (Erk) were significantly increased in S. aureus-stimulated bMECs. It indicated that S. aureus activated NF-κB and MAPK signaling pathway. We also examined the effects of Se on the phosphorylation of IκBα, p65, p38 and Erk in NF-κB and MAPK signaling pathway, which have well been proved to control the synthesis and release of pro-inflammatory mediators during inflammation. The findings are exciting, that pretreatment with Se (4, 8 μM) significantly suppressed the phosphorylation of IκBα, p65, p38 and Erk.

CONCLUSIONS

These results suggest that Se down-regulates inflammatory mediators TNF-α, IL-1β and IL-6 gene expressions via TLR2, NF-κB and MAPK signaling pathway in S. aureus-stimulated bMECs, which may be responsible for the anti-inflammatory effect of Se.

Invited review: Low milk somatic cell count and susceptibility to mastitis

An enduring controversy exists about low milk cell counts and susceptibility to mastitis. The concentration of milk leukocytes, or somatic cell count (SCC), is a well-established direct indicator of mammary gland inflammation that is highly correlated with the presence of a mammary infection. The SCC is also used as a trait for the selection of dairy ruminants less prone to mastitis. As selection programs favor animals with less SCC, and as milk cells contribute to the defense of the mammary gland, the idea that susceptibility to mastitis could possibly be increased in the long term has been put forward and is still widely debated. Epidemiological and experimental studies aimed at relating SCC to susceptibility to mastitis have yielded results that seem contradictory at first sight. Nevertheless, by taking into account the immunobiology of milk and mammary tissue cells and their role in the defense against infection, along with recent studies on SCC-based divergent selection of animals, the issue can be settled. Apparent SCC-linked susceptibility to mastitis is a phenotypic trait that may be linked to immunomodulation but not to selection.

TLR ligands, but not modulators of histone modifiers, can induce the complex immune response pattern of endotoxin tolerance in mammary epithelial cells

Excessive stimulation of the TLR4 axis through LPS reduces the expression of some cytokine genes in immune cells, while stimulating the expression of immune defense genes during a subsequent bacterial infection. This endotoxin tolerance (ET) is mediated via epigenetic mechanisms. Priming the udder of cows with LPS was shown to induce ET in mammary epithelial cells (MEC), thereby protecting the udder against reinfection for some time. Seeking alternatives to LPS priming we tried to elicit ET by priming MEC with either lipopeptide (Pam2CSK4) via the TLR2/6 axis or inhibitors of histone-modifying enzymes. Pre-incubation of MEC with Pam2CSK4 enhanced baseline and induced expression of bactericidal (β-defensin; SLPI) and membrane protecting factors (SAA3, TGM3), while reducing the expression of cytokine- and chemokine-encoding genes (TNF, IL1β) after a subsequent pathogen challenge, the latter, however, not as efficiently as after LPS priming. Pre-treating MEC with various inhibitors of histone H3 modifiers (for demethylation, acetylation or deacetylation) all failed to induce any of the protective factors and only resulted in some dampening of cytokine gene expression after the re-challenge. Hence, triggering immune functions via the TLR axis, but not through those histone modifiers, induced the beneficial phenomenon of ET in MEC.

Rumen-derived lipopolysaccharide enhances the expression of lingual antimicrobial peptide in mammary glands of dairy cows fed a high-concentrate diet

BACKGROUND

Long-term high-concentrate diet (HCD) feeding can cause subacute ruminal acidosis in cows and subsequently trigger systemic inflammatory and immune responses. Therefore, we conducted the present study in which twelve lactating cows installed with ruminal fistula were randomly assigned to the HCD group (forage:concentrate = 4:6, n = 6) or the low-concentrate diet (LCD) group (forage:concentrate = 6:4, n = 6) and were fed for 20 weeks. Ruminal fluid, plasma and mammary gland tissue samples were collected at week 20 for analysing lipopolysaccharide (LPS), pro-inflammatory cytokines, and immune relevant gene expression. The aim of this study was to investigate the effect of rumen-derived LPS on lingual antimicrobial peptide (LAP) synthesis and immune responses in mammary glands of lactating cows fed a HCD.

RESULTS

Compared with the LCD group, the ruminal pH was lower in the HCD group, while LPS concentrations in the rumen, lacteal artery and vein were higher. The expression of LAP, BNBD5, IL-1β, IL-6, IL-8, and TNF-α was enhanced in the HCD group. LAP protein expression was higher in the HCD group than that in the LCD group. The expression of nuclear factor kappa B (NF-кB) did not change, but was activated, as the amounts of phosphorylated NF-kB and phosphorylated inhibitory kBα increased in the HCD group compared with that in the LCD group.

CONCLUSIONS

After long-term HCD feeding, rumen-derived LPS translocated to the blood stream, triggered inflammatory and immune responses and enhanced LAP synthesis via the NF-kB signalling pathway in mammary glands of lactating cows.

Comparison of the pathogen species-specific immune response in udder derived cell types and their models

The outcome of an udder infection (mastitis) largely depends on the species of the invading pathogen. Gram-negative pathogens, such as Escherichia coli often elicit acute clinical mastitis while Gram-positive pathogens, such as Staphylococcus aureus tend to cause milder subclinical inflammations. It is unclear which type of the immune competent cells residing in the udder governs the pathogen species-specific physiology of mastitis and which established cell lines might provide suitable models. We therefore profiled the pathogen species-specific immune response of different cell types derived from udder and blood. Primary cultures of bovine mammary epithelial cells (pbMEC), mammary derived fibroblasts (pbMFC), and bovine monocyte-derived macrophages (boMdM) were challenged with heat-killed E. coli, S. aureus and S. uberis mastitis pathogens and their immune response was scaled against the response of established models for MEC (bovine MAC-T) and macrophages (murine RAW 264.7). Only E. coli provoked a full scale immune reaction in pbMEC, fibroblasts and MAC-T cells, as indicated by induced cytokine and chemokine expression and NF-κB activation. Weak reactions were induced by S. aureus and none by S. uberis challenges. In contrast, both models for macrophages (boMdM and RAW 264.7) reacted strongly against all the three pathogens accompanied by strong activation of NF-κB factors. Hence, the established cell models MAC-T and RAW 264.7 properly reflected key aspects of the pathogen species-specific immune response of the respective parental cell type. Our data imply that the pathogen species-specific physiology of mastitis likely relates to the respective response of MEC rather to that of professional immune cells.

Extracellular milieu grossly alters pathogen-specific immune response of mammary epithelial cells

BACKGROUND

Considerably divergent data have been published from attempts to model the E. coli vs. S. aureus specific immune reaction of the udder using primary cultures of bovine mammary epithelial cells from cows (pbMEC). Some groups reported a swift, strong and transient inflammatory response against challenges with E. coli and only a weak and retarded response against S. aureus, in agreement with the respective reaction of the udder. Others found almost the reverse. Presence or absence of fetal calf serum distinguished the experimental setting between both groups. We examined here if this causes the divergent reaction of the pbMEC towards both pathogen species. We challenged pbMEC with proteins from heat killed E. coli or S. aureus pathogens or purified TLR2 and TLR4 ligands. The stimuli were applied in normal growth medium with (SM10) or without (SM0) 10% fetal calf serum, or in the basal medium supplemented with 10 mg/ml milk proteins (SM Milk).

RESULTS

Withdrawal of FCS slowed down and decreased the extent by which E. coli or LPS enhanced the expression of cyto- and chemokine encoding genes through impaired TLR4 signalling but enforced their expression during stimulation with S. aureus. SM Milk strongly quenched the induction of those genes. S. aureus strain specific differences in the reaction of the pbMEC could only be recorded in SM0. NF-κB factors were activated by E. coli in all stimulation media, but only to a small extent by S. aureus, solely in SM0. Purified ligands for TLR2 stimulated expression of those genes and activated NF-κB equally well in SM10 and SM0. The mRNA destabilizing factor tristetraproline was only induced by E. coli in SM10 and by purified PAMPs.

CONCLUSIONS

Our data cross validate the correctness of previously published divergent data on the pathogen-specific induction of key immune genes in pbMEC. The differences are due to the presence of FCS, modulating signalling through TLR4 and TLR-unrelated pathogen receptors. S. aureus does not substantially activate any TLR signalling in MEC. Rather, receptors distinct from TLRs perceive the presence of S. aureus and control the immune response against this pathogen in MEC.

Association of IL8 -105G/A with mastitis somatic cell score in Chinese Holstein dairy cows

The single nucleotide polymorphisms (SNPs) in the 5' upstream of bovine IL8 gene were investigated in 810 Chinese Holstein cows from 35 bull families in a dairy farm in Shanghai using polymerase chain reaction-single strand conformation polymorphism (PCR-SSCP) technique. The Real-time PCR and Western blot were used to detect the mRNA and protein levels of genotype Chinese Holstein dairy cows. The results showed that one SNP -105G>A was detected, designating three genotypes (GG, GA and AA) with respective frequencies of 0.38, 0.46, and 0.16. The significant association of the SNP -105G>A with somatic cell score (SCS) was identified. Genotype GG had a significantly lower SCS than genotype GA or AA (P < 0.01), and the relative mRNA expression and protein level of GG was found to be the highest. These results suggest that the genotype GG may be a useful genetic marker for mastitis resistance selection and breeding in Chinese Holstein dairy cows.

Unmasking Upstream Gene Expression Regulators with miRNA-corrected mRNA Data

Expressed micro-RNA (miRNA) affects messenger RNA (mRNA) abundance, hindering the accuracy of upstream regulator analysis. Our objective was to provide an algorithm to correct such bias. Large mRNA and miRNA analyses were performed on RNA extracted from bovine liver and mammary tissue. Using four levels of target scores from TargetScan (all miRNA:mRNA target gene pairs or only the top 25%, 50%, or 75%). Using four levels of target scores from TargetScan (all miRNA:mRNA target gene pairs or only the top 25%, 50%, or 75%) and four levels of the magnitude of miRNA effect (ME) on mRNA expression (30%, 50%, 75%, and 83% mRNA reduction), we generated 17 different datasets (including the original dataset). For each dataset, we performed upstream regulator analysis using two bioinformatics tools. We detected an increased effect on the upstream regulator analysis with larger miRNA:mRNA pair bins and higher ME. The miRNA correction allowed identification of several upstream regulators not present in the analysis of the original dataset. Thus, the proposed algorithm improved the prediction of upstream regulators.

Expression patterns of β-defensin and cathelicidin genes in parenchyma of bovine mammary gland infected with coagulase-positive or coagulase-negative Staphylococci

BACKGROUND

Mastitis is still considered to be the most economically important infectious disease in dairy cattle breeding. The immune response in mammary gland tissues could help in developing support strategies to combat this disease. The role of neutrophils and macrophages in the innate response of mammary gland is well known. However, the immune response in mammary gland tissues, including levels of antimicrobial peptide transcripts, has not been well recognized. Moreover, most studies are conducted in vitro, on cell cultures, or on artificially infected animals, with analysis being done within a several dozen hours after infection.The aim of the study was to examine the in vivo transcript levels of beta-defensin and cathelicidins genes in cow mammary gland secretory tissue (parenchyma) with the chronic, recurrent and incurable mammary gland inflammation induced by coagulase-positive or coagulase-negative Staphyloccoci vs. bacteria-free tissue.

RESULTS

The mRNA of DEFB1, BNBD4, BNBD5, BNBD10 and LAP genes, but not of TAP gene, were detected in all investigated samples regardless of the animals' age and microbiological status of the mammary gland, but at different levels. The expression of most of the beta-defensin genes was shown to be much higher in tissues derived from udders infected with bacteria (CoPS or CoNS) than from bacteria-free udders, regardless of parity. Cathelicidins (CATH4, CATH5 and CATH6) showed expression patterns contrasting those of β-defensins, with the highest expression in tissues derived from bacteria-free udders.

CONCLUSION

Increased expression of genes encoding β-defensins in the infected udder confirms their crucial role in the defense of the cow mammary gland against mastitis. On the other hand, the elevated cathelicidin transcripts in non-infected tissues indicate their role in the maintenance of healthy mammary tissues. The expression levels of investigated genes are likely to depend on the duration of the infection and type of bacteria.

Contribution of mammary epithelial cells to the immune response during early stages of a bacterial infection to Staphylococcus aureus

To differentiate between the contribution of mammary epithelial cells (MEC) and infiltrating immune cells to gene expression profiles of mammary tissue during early stage mastitis, we investigated in goats the in vivo transcriptional response of MEC to an experimental intra mammary infection (IMI) with Staphylococcus aureus, using a non-invasive RNA sampling method from milk fat globules (MFG). Microarrays were used to record gene expression patterns during the first 24 hours post-infection (hpi). This approach was combined with laser capture microdissection of MEC from frozen slides of mammary tissue to analyze some relevant genes at 30 hpi. During the early stages post-inoculation, MEC play an important role in the recruitment and activation of inflammatory cells through the IL-8 signalling pathway and initiate a sharp induction of innate immune genes predominantly associated with the pro-inflammatory response. At 30 hpi, MEC express genes encoding different acute phase proteins, including SAA3, SERPINA1 and PTX3 and factors, such as S100A12, that contribute directly to fighting the infection. No significant change in the expression of genes encoding caseins was observed until 24 hpi, thus validating our experimental model to study early stages of infection before the occurrence of tissue damage, since the milk synthesis function is still operative. This is to our knowledge the first report showing in vivo, in goats, how MEC orchestrate the innate immune response to an IMI challenge with S. aureus. Moreover, the non-invasive sampling method of mammary representative RNA from MFG provides a valuable tool to easily follow the dynamics of gene expression in MEC to search for sensitive biomarkers in milk for early detection of mastitis and therefore, to successfully improve the treatment and thus animal welfare.

Lipopolysaccharide priming enhances expression of effectors of immune defence while decreasing expression of pro-inflammatory cytokines in mammary epithelia cells from cows

Background

Udder infections with environmental pathogens like Escherichia coli are a serious problem for the dairy industry. Reduction of incidence and severity of mastitis is desirable and mild priming of the immune system either through vaccination or with low doses of immune stimulants such as lipopolysaccharide LPS was previously found to dampen detrimental effects of a subsequent infection. Monocytes/macrophages are known to develop tolerance towards the endotoxin LPS (endotoxin tolerance, ET) as adaptation strategy to prevent exuberant inflammation.

We have recently observed that infusion of 1 μg of LPS into the quarter of an udder effectively protected for several days against an experimentally elicited mastitis. We have modelled this process in primary cultures of mammary epithelial cells (MEC) from the cow. MEC are by far the most abundant cells in the healthy udder coming into contact with invading pathogens and little is known about their role in establishing ET.

Results

We primed primary MEC cultures for 12 h with LPS (100 ng/ml) and stimulated three cultures either 12 h or 42 h later with 10⁷/ml particles of heat inactivated E. coli bacteria for six hours. Priming-related alterations in the global transcriptome of those cells were quantified with Affymetrix microarrays. LPS priming alone caused differential expression of 40 genes and mediated significantly different response to a subsequent E. coli challenge of 226 genes. Expression of 38 genes was enhanced while that of 188 was decreased. Higher expressed were anti-microbial factors (β-defensin LAP, SLPI), cell and tissue protecting factors (DAF, MUC1, TGM1, TGM3) as well as mediators of the sentinel function of MEC (CCL5, CXCL8). Dampened was the expression of potentially harmful pro-inflammatory master cytokines (IL1B, IL6, TNF-α) and immune effectors (NOS2, matrix metalloproteases). Functional network analysis highlighted the reduced expression of IL1B and of IRF7 as key to this modulation.

Conclusion

LPS-primed MEC are fitter to repel pathogens and better protected against misguided attacks of the immune response. Attenuated is the exuberant expression of factors potentially promoting immunopathological processes. MEC therefore recapitulate many aspects of ET known so far from professional immune cells.

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.

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.

Lingual antimicrobial peptide and IL-8 expression are oppositely regulated by the antagonistic effects of NF-κB p65 and C/EBPβ in mammary epithelial cells

Pathogen contact induces quickly in Mammary Epithelial Cells (MEC) the expression of the proinflammatory cytokine IL-8 and delayed that of the bactericidal β-defensin LAP. Both genes encoding these factors feature on their proximal promoter a composite NF-κB/CEBP binding site. We compare here in MEC the role of NF-κB and C/EBP factors in regulating basal and pathogen-induced expression of both genes from cattle. Abrogating NF-κB binding to that site by introduction of a single point mutation blocks promoter activity of both genes in reporter gene assays. Chromatin accessibility PCR and Chromatin immunoprecipitation reveal that the chromatin of the resting LAP promoter is tightly packed and NF-κB p50 homodimer binding prevails. Infection results in chromatin decompaction accompanied by predominant recruitment of NF-κB p65 for promoter activation. Overexpression of transcription factors confirms a stimulatory role of NF-κB p65 but also a repressive function of C/EBPβ for LAP promoter activity. These factors reverse roles to control IL-8 expression. NF-κB p65 homodimers already reside on the resting IL-8 promoter and induction recruits NF-κB p50. Overexpression of both NF-κB factors represses the promoter in MEC, but not in HEK293 cells. Inhibitors of NF-κB activation and nuclear recruitment both tremendously increase basal and pathogen stimulated IL-8 mRNA concentrations in MEC. Mutation of the C/EBP-binding site blocks and overexpression of C/EBPβ stimulates IL-8-promoter activity. Thus, the pathogen-induced fast activation of diverse transcription factors acting through a common promoter binding site is gene specifically differentiated into opposite functional significance for swiftly (IL-8) or slowly (LAP) induced genes in MEC.

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.