Immune defenses of the mammary gland epithelium of dairy ruminants

Immunology of the Bovine Mammary Gland: Advances in Recent Years

Bovine mastitis remains the most costly disease in the dairy industry due to its impact on milk production, milk quality, and animal welfare. Optimal immunity is essential for the mammary gland to resist infections, efficiently clear them, and limit damage to mammary tissue. This article highlights recent advancements built on previous knowledge exploring opportunities for enhancing mammary gland immune responses. Ultimately, these improvements aim to increase the resistance of the mammary gland to infections and reduce the costs associated with this disease in the dairy industry.

Anti-inflammatory effects of apigenin on LPS-induced mastitis in lactating SD rats through inhibiting TLR4/NF-κB signaling pathway

Mastitis is an important disease of the mammary gland in all kinds of lactating mammals, endangering the development of animal husbandry and human health. Apigenin is one chemical constituent of Taraxacum and Philippine Violet Herb which are effective Chinese herbs for the treatment of mastitis. It is reported that apigenin possesses anti-inflammatory activity and other pharmacological effects. However, the attenuation of apigenin on mastitis has not yet been reported. The present study investigated the protection of apigenin against lipopolysaccharide (LPS)-induced mastitis in SD rats both in vivo and in vitro. The results suggested that apigenin relieved the lesions of mammary tissues induced by LPS, decreased mRNA and protein levels of pro-inflammatory cytokines:tumor necrosis factor-alpha (TNF-α), interleukin-1β (IL-1β), and interleukin-6 (IL-6). Simultaneously, apigenin reduced the increasing content of myeloperoxidase (MPO) and Toll-like receptor 4 (TLR4), and phosphorylation of nuclear factor kappa B (NF-κB) induced by LPS. The results showed that apigenin was able to attenuate the LPS-induced mastitis in rats by inhibiting the TLR4/NF-κB signaling pathway in vivo and in vitro, which provides scientific references for further research.

Berberine and Cyperus rotundus extract nanoformulations protect the rats against Staphylococcus-induced mastitis via antioxidant and anti-inflammatory activities: role of MAPK signaling

Berberine (BER) and Cyperus rotundus rhizomes extract (CRE) are phytochemicals characterized by broad-spectrum pharmacological activity that could tackle the side effects of conventional mastitis therapies, however, they undergo a modest bioavailability. In the current study, nanoformulations of BER and CRE chitosan hydrogel (BER/CH-NPs, CRE/CH-NPs) were investigated for their antibacterial, antioxidant, anti-inflammatory and anti-apoptotic effects against S. aureus-induced mastitis in a rat model. The experiment was conducted on 80 early lactating female albino rats allocated into 6 groups; control, mastitis, BER/CH-NPs (1 and 0.5 mg), CRE/CH-NPs (0.5 and 0.25 mg), BER/CH-NPs + CRE/CH-NPs (0.5 + 0.25 and 0.25 + 0.125 mg). The nanoparticles were given by oral gavage once every other day from day 2 to day 12 after parturition. On the 13th day, intra-mammary inoculation with 100 µl of S. aureus suspension containing 2.1 × 108 CFU/ml in all groups except the control group. The results expressed the effect of BER/CH-NPs and CRE/CH-NPs on mammary gland tissue including significantly diminished viable bacterial load as well as attenuated the levels of MPO, MDA, caspase-3 with elevating Nrf2 level, and modulating glutathione redox. Also, the nanoformulations resulted in attenuation of the mRNA expression of TLR2, NOD2, Keap-1 and MAPK signaling pathway additional to the immune reactivity of NF-κB P65 and p-ERK as well as the preservation of the regular alveolar architecture. The supplementation of the berberine and Cyperus rotundus extract nanoformulations could be a prospective protective approach against Staphylococcal mastitis via their antibacterial, antioxidant, antiapoptotic, anti-inflammatory and modulation of MAPK signaling pathway.

Invited review: Mastitis Escherichia coli strains-Mastitis-associated or mammo-pathogenic?

Bovine mastitis remains a major concern for dairy farmers, mainly because of its effect on the economy of their activity and on animal welfare. Because Escherichia coli is considered a major mastitis pathogen, the diversity of E. coli strains isolated from mastitis cases has been studied for decades, with the aim to discover new ways to fight this infection. With the recent advances in whole-genome sequencing, a detailed view of the peculiarities of mastitis E. coli strains has emerged. This review aims to bring together the knowledge garnered over the years with the more recent results of whole-genome analyses. Whereas the concept of a mammary pathogenic E. coli has been proposed, because a common set of virulence genes cannot be identified among mastitis E. coli strains, we prefer the use of mastitis-associated E. coli (MAEC), with MAEC being more an "ecotype" rather than a "pathotype." Indeed, data available so far suggest that a common feature of MAEC would rather be an enrichment in fitness capabilities that makes them well-suited for survival and rapid adaptation to changing biotopes in the mammary gland, which we qualify as intramammary ecotopes.

Dairy cows develop protective immunity against reinfection with bovine H5N1 influenza virus

Infection of highly pathogenic avian influenza (HPAI) H5N1 clade 2.3.4.4b in dairy cows causes severe mastitis and milk production losses. Whether cows can develop protective immunity is unclear. Here we infected three lactating cows with HPAI H5N1 genotype B3.13 via the hindquarters of the udder to mimic intra-mammary infection. Inoculated cows displayed clinical responses consistent with affected dairy herds in the United States including virus shedding almost exclusively in inoculated hindquarters that peaked between Days 2-4 post inoculation and gradually declined by Day 21. Histologically, peak virus shedding in milk corresponded with severe acute necrotic mastitis in the inoculated hindquarters but not in the uninoculated forequarters. Two cows were reinfected with HPAI H5N1 virus at unaffected forequarters following resolution of infection. Secondary inoculation did not result in clinical manifestations or virus shedding in milk. Virus-neutralizing antibodies were detected at Day 14 post inoculation in milk with higher titres observed in the inoculated hindquarters relative to the forequarters. We also detected HPAI H5N1 viral RNA in air samples from animal rooms during routine husbandry activity. These data indicate that primary infection via intra-mammary inoculation can generate protective immunity against bovine HPAI H5N1 virus in dairy cows.

Influenza A virus in dairy cattle: infection biology and potential mammary gland-targeted vaccines

Influenza, a major "One Health" threat, has gained heightened attention following recent reports of highly pathogenic avian influenza in dairy cattle and cow-to-human transmission in the USA. This review explores general aspects of influenza A virus (IAV) biology, its interactions with mammalian hosts, and discusses the key considerations for developing vaccines to prevent or curtail IAV infection in the bovine mammary gland and its spread through milk.

Saccharomyces cerevisiae as a platform for vaccination against bovine mastitis

Mastitis is a major issue for the dairy industry. Despite multiple attempts, the efficacy of available mastitis vaccines is limited and this has been attributed to their incapacity to trigger robust cell-mediated immunity. Yeasts have recently been identified as promising antigen vectors capable of inducing T-cell responses, surpassing the antibody-biased mechanisms elicited by conventional adjuvanted vaccines. In this study, we combine in vitro, ex vivo, and in vivo approaches to evaluate the potential of the yeast Saccharomyces cerevisiae as a platform for novel vaccines against bovine mastitis. We demonstrate that S. cerevisiae is safe for intramuscular and intramammary immunisation in dairy cows. Vaccination resulted in a significant increase of IFNγ and IL-17 responses against the yeast platform but not against the vaccine antigen. These observations highlight that strategies to counterbalance the immunodominance of S. cerevisiae antigens are necessary for the development of successful vaccine candidates.

Endolysin NC5 improves early cloxacillin treatment in a mouse model of Streptococcus uberis mastitis

Streptococcus uberis frequently causes bovine mastitis, an infectious udder disease with significant economic implications for dairy cows. Conventional antibiotics, such as cloxacillin, sometimes have limited success in eliminating S. uberis as a stand-alone therapy. To address this challenge, the study objective was to investigate the VersaTile engineered endolysin NC5 as a supplemental therapy to cloxacillin in a mouse model of bovine S. uberis mastitis. NC5 was previously selected based on its intracellular killing and biofilm eradicating activity. To deliver preclinical proof-of-concept of this supplemental strategy, lactating mice were intramammarily infected with a bovine S. uberis field isolate and subsequently treated with cloxacillin (30.0 μg) combined with either a low (23.5 μg) or high (235.0 μg) dose of NC5. An antibiotic monotherapy group, as well as placebo treatment, was included as controls. Two types of responders were identified: fast (n = 17), showing response after 4-h treatment, and slow (n = 10), exhibiting no clear response at 4 h post-treatment across all groups. The high-dose combination therapy in comparison with placebo treatment impacted the hallmarks of mastitis in the fast responders by reducing (i) the bacterial load 13,000-fold (4.11 ± 0.78 Δlog10; p < 0.001), (ii) neutrophil infiltration 5.7-fold (p > 0.05), and (iii) the key pro-inflammatory chemokine IL-8 13-fold (p < 0.01). These mastitis hallmarks typically followed a dose response dependent on the amount of endolysin added. The current in vivo study complements our in vitro data and provides preclinical proof-of-concept of NC5 as an adjunct to intramammary cloxacillin treatment. KEY POINTS: • Engineered endolysin NC5 was preclinically evaluated as add-on to cloxacillin treatment. • Two types of mice (slow and fast responding) were observed. • The add-on treatment decreased bacterial load, neutrophil influx, and pro-inflammatory mediators.

Omonijo F, A Ganai N, M. Ibeagha-Awemu E, Mudasir Ahmad S. Immunotherapy in mastitis: state of knowledge, research gaps and way forward

Mastitis is an inflammatory condition that affects dairy cow's mammary glands. Traditional treatment approaches with antibiotics are increasingly leading to challenging scenarios such as antimicrobial resistance. In order to mitigate the unwanted side effects of antibiotics, alternative strategies such as those that harness the host immune system response, also known as immunotherapy, have been implemented. Immunotherapy approaches to treat bovine mastitis aims to enhance the cow's immune response against pathogens by promoting pathogen clearance, and facilitating tissue repair. Various studies have demonstrated the potential of immunotherapy for reducing the incidence, duration and severity of mastitis. Nevertheless, majority of reported therapies are lacking in specificity hampering their broad application to treat mastitis. Meanwhile, advancements in mastitis immunotherapy hold great promise for the dairy industry, with potential to provide effective and sustainable alternatives to traditional antibiotic-based approaches. This review synthesizes immunotherapy strategies, their current understanding and potential future perspectives. The future perspectives should focus on the development of precision immunotherapies tailored to address individual pathogens/group of pathogens, development of combination therapies to address antimicrobial resistance, and the integration of nano- and omics technologies. By addressing research gaps, the field of mastitis immunotherapy can make significant strides in the control, treatment and prevention of mastitis, ultimately benefiting both animal and human health/welfare, and environment health.

In vivo and in vitro anti-inflammation of Rhapontici Radix extract on mastitis via TMEM59 and GPR161

ETHNOPHARMACOLOGICAL RELEVANCE

Rhapontici Radix ethanol extract (RRE) is derived from the dried root of Rhaponticum uniflorum (L.) DC belonging to the Asteraceae family. RRE exhibits significant anti-inflammatory and antioxidant properties; however, the potential of RRE in mastitis treatment requires further investigation.

AIM OF THIS STUDY

This research was performed to examine the protective properties of RRE against mastitis and the mechanisms underlying the effects of RRE.

MATERIAL AND METHODS

RRE components were analyzed by HPLC-MS/MS and DPPH methods. Isochlorogenic acid B (ICAB) was obtained commercially. MTT assay was utilized to assess RRE or ICAB cytotoxicity in bovine mammary alveolar (MAC-T) cells. Immunohistochemistry were used to investigate the pathological alterations in mammary tissue. The protein levels of inflammatory cytokines and mediators were analyzed using ELISA, and the expression of MAPK and NF-κB signaling pathways, as well as p65 nuclear translocation, were analyzed through Western blotting and immunofluorescence techniques, respectively. Target proteins of RRE were screened by RNA-seq and tandem mass tag analyses. Protein interaction was revealed and confirmed using co-immunoprecipitation and CRISPR/Cas9-based knockdown and overexpression of target genes.

RESULTS

ICAB was revealed as one of the main components in RRE, and it was responsible for 84.33% of RRE radical scavenging activity. Both RRE and ICAB mitigated the infiltration of T lymphocytes in the mammary glands of mice, leading to decreased levels of inflammatory mediators (COX-2 and iNOS) and cytokines (TNF-α, IL-6, and IL-1β) in lipopolysaccharide (LPS)-induced MAC-T cells. Furthermore, RRE and ICAB suppressed the LPS-induced phosphorylation of NF-κB inhibitor and p65, thereby impeding p65 nuclear translocation in mouse mammary glands and MAC-T cells. In addition, RRE and ICAB attenuated the LPS-triggered activation of c-Jun N-terminal kinase 1/2, p38, and extracellular regulated protein kinase 1/2. Importantly, co-treated with LPS and ICAB in MAC-T cells, an upregulation of G-protein coupled receptor 161 (GPR161) and transmembrane protein 59 (TMEM59) was observed; the interact between TMEM59 and was found, leading to inhibition of NF-κB activity and inflammatory cytokine production.

CONCLUSION

ICAB is a prominent antioxidant in RRE. RRE and ICAB reduce mammary inflammation via MAPK and NF-κB pathways and the interaction between TMEM59 and GPR161 mediates the control of ICAB in NF-κB signaling.

Mitigative Effect and Mechanism of Caffeic Acid Combined with Umbilical Cord-Mesenchymal Stem Cells on LPS-Induced Mastitis

Mastitis is an inflammation of the mammary gland tissue that can lead to decreased milk production and altered milk composition, carrying serious implications for the safety of dairy products. Although both caffeic acid (CA) and umbilical cord-mesenchymal stem cells (UC-MSCs) showed potential anti-inflammatory and immunomodulatory properties, little is known about their combined roles in treating mastitis. Here, we report the combined effects and mechanisms of CA and UC-MSCs on lipopolysaccharide (LPS)-induced mastitis. Based on the network pharmacological analysis, the potential relevant genes involved in the alleviating effects of CA on LPS-induced mastitis were inferred. In LPS-treated mammary epithelial cells, CA or/and UC-MSC conditioned medium (UC-MSC-CM) inhibited the phosphorylation of p65, p50, p38, IκB, and MKK3/6 proteins and the expression of downstream inflammatory factors TNF-α, IL-1β, IL-6, IL-8, and COX-2. Additionally, CA or/and hydrogel-loaded UC-MSCs also suppressed the activation of the above inflammatory pathway, leading to the alleviation of pathological damages in the LPS-induced mouse mastitis model. UC-MSCs exhibited more significant effects than CA, and the combined treatment of both was more effective. Our study sheds light on the synergistic and complementary effects of CA and UC-MSCs in alleviating mastitis, offering clues for understanding the regulation of the p38-MAPK/NF-κB↔TNF-α signal transduction loop in the tumor necrosis factor (TNF) pathway as a potential mechanism. This study provides a theoretical basis for developing a novel antibiotic alternative treatment of mastitis that may contribute to reducing economic losses in animal husbandry and protecting public health safety.

Difenoconazole Induced Damage of Bovine Mammary Epithelial Cells via ER Stress and Inflammatory Response

Difenoconazole (DIF) is a fungicide used to control various fungi. It is absorbed on the surface of different plants and contributes significantly to increased crop production. However, DIF is reported to exhibit toxicity to fungi and to aquatic plants, fish, and mammals, including humans, causing adverse effects. However, research on the impact of DIF on the mammary epithelial cells of herbivorous bovines is limited. DIF-induced damage and accumulation in the mammary glands can have direct and indirect effects on humans. Therefore, we investigated the effects and mechanisms of DIF toxicity in MAC-T cells. The current study revealed that DIF reduces cell viability and proliferation while triggering apoptotic cell death through the upregulation of pro-apoptotic proteins, including cleaved caspase 3 and Bcl-2-associated X protein (BAX), and the downregulation of leukemia type 2 (BCL-2). DIF also induced endoplasmic reticulum (ER) stress by increasing the expression of genes or proteins of Bip/GRP78, protein disulfide isomerase (PDI), activating transcription factor 4 (ATF4), C/EBP homologous protein (CHOP), and endoplasmic reticulum oxidoreductase 1 Alpha (ERO1-Lα). We demonstrated that DIF induces mitochondria-mediated apoptosis in MAC-T cells by activating ER stress pathways. This cellular damage resulted in a significant increase in the expression of inflammatory response genes and proteins, including cyclooxygenase 2 (COX2), transforming growth factor beta 3 (TGFB3), CCAAT enhancer binding protein delta (CEBPD), and iNOS, in DIF-treated groups. In addition, spheroid formation by MAC-T cells was suppressed by DIF treatment. Our findings suggest that DIF exposure in dairy cows may harm mammary gland function and health and may indirectly affect human consumption of milk.

Bioactive Compounds and Probiotics Mitigate Mastitis by Targeting NF-κB Signaling Pathway

Mastitis is a significant inflammatory condition of the mammary gland in dairy cows. It is caused by bacterial infections and leads to substantial economic losses worldwide. The disease can be either clinical or sub-clinical and presents challenges such as reduced milk yield, increased treatment costs, and the need to cull affected cows. The pathogenic mechanisms of mastitis involve the activation of Toll-like receptors (TLRs), specifically TLR2 and TLR4. These receptors play crucial roles in recognizing pathogen-associated molecular patterns (PAMPs) and initiating immune responses through the NF-κB signaling pathway. Recent in vitro studies have emphasized the importance of the TLR2/TLR4/NF-κB signaling pathway in the development of mastitis, suggesting its potential as a therapeutic target. This review summarizes recent research on the role of the TLR2/TLR4/NF-κB signaling pathway in mastitis. It focuses on how the activation of TLRs leads to the production of proinflammatory cytokines, which, in turn, exacerbate the inflammatory response by activating the NF-κB signaling pathway in mammary gland tissues. Additionally, the review discusses various bioactive compounds and probiotics that have been identified as potential therapeutic agents for preventing and treating mastitis by targeting TLR2/TLR4/NF-κB signaling pathway. Overall, this review highlights the significance of targeting the TLR2/TLR4/NF-κB signaling pathway to develop effective therapeutic strategies against mastitis, which can enhance dairy cow health and reduce economic losses in the dairy industry.

Localized mammary gland changes in milk composition and venous blood metabolite concentrations result from sterile subclinical mastitis

Subclinical mastitis reduces milk yield and elicits undesirable changes in milk composition, but the mechanisms resulting in reduced milk production in affected mammary glands are incompletely understood. This study investigated the effects of sterile inflammation on mammary gland metabolism by assessing changes in milk and venous blood composition. Mid-lactation primiparous Holstein cows (n = 4) had udder halves randomly allocated to treatments; quarters of 1 udder half were infused with 2 billion cfu of formalin-fixed Staphylococcus aureus (FX-STAPH) and quarters of the opposite udder half were infused with saline (SAL). Blood samples were collected from the right and left subcutaneous abdominal veins in 2.6 h intervals until 40 h postchallenge and analyzed for blood gas and metabolite concentrations. Milk from FX-STAPH udder halves had significantly increased SCS by the first milking at 8 h postchallenge. By 16 h postchallenge, FX-STAPH udder halves had increased concentrations of protein and lactate and lower lactose concentrations than SAL udder halves. Milk fat concentrations, milk yields, ECM yields, and the ferric reducing antioxidant power of milk were not significantly different between SAL and FX-STAPH udder halves. Venous blood of FX-STAPH halves had marginally greater concentrations of saturated O2, partial pressures of O2, and glucose concentrations than SAL halves. Conversely, total and partial pressures of CO2 did not differ between udder half treatments, suggesting a shift in local metabolite utilization in FX-STAPH udder halves. These results indicate that changes in milk composition resulting from mastitis are accompanied by changes in some key blood metabolite concentrations. The shift in venous blood metabolite concentrations, along with the marked increase in milk lactate, suggests that local mammary tissue or recruited immune cells, or both, alter metabolite usage in mammary tissues. Future studies are needed to quantify the uptake of key milk precursors during mastitis.

Short communication: Goat mastitis and the formation of neutrophil extracellular traps (NETs)

Mastitis, an inflammation of the mammary gland affecting milk production and quality in dairy herds, is often associated with Staphylococcus spp. in goats. Neutrophils are crucial in combating infections by migrating into milk and deploying various defense strategies, including the release of neutrophil extracellular traps (NETs) composed of DNA, histones, and bactericidal proteins. This study investigated whether NETs are released by goat neutrophils stimulated in vitro by Staphylococcus aureus and Staphylococcus warneri, two common pathogens of goat mastitis. PMNs were isolated from blood from healthy adult goats. We evaluated goat NET formation by stimulating cells with: phorbol 12-myristate 13-acetate (PMA) as a positive control, cytochalasin for inhibition of actin polymerization, S. aureus, and S. warneri. NET formation was observed in response to chemical stimulation and bacterial presence, effectively trapping pathogens. Variations in NET formation between S. aureus and S. warneri suggest pathogen-specific responses. These findings suggest that the formation of NETs may be an important complementary mechanism in the defense against mastitis in goats. In conclusion, this study unveils a novel defense mechanism in goats, indicating the role of NETs against S. aureus and S. warneri in mastitis.

Innate immune response of bovine mammary epithelial cells in Mycoplasma bovis mastitis using an in vitro model of bovine mammary gland infection

Mycoplasma bovis mastitisis highly contagious and disrupts lactation, posing a significant threat to the dairy industry. While the mammary gland's defence mechanism involves epithelial cells and mononuclear cells (MNC), their interaction with M. bovis remains incompletely understood. In this study, we assessed the immunological reactivity of bovine mammary epithelial cells (bMEC) to M. bovis through co-culture with MNC. Upon co-culture with MNC, the mRNA expression levels of interleukin (IL)-1β, IL-6, IL-8 and tumor necrosis factor (TNF)-α in bMEC stimulated by M. bovis showed a significant increase compared to monoculture. Additionally, when stimulated with M. bovis, the culture supernatant exhibited significantly higher concentrations of IL-6 and interferon (IFN)-γ, while IL-1β concentration tended to be higher in co-culture with MNC than in monoculture. Furthermore, the mRNA expression levels of toll-like receptor (TLR) 2 in bMEC stimulated with M. bovis tended to increase, and TLR4 significantly increased when co-cultured with MNC compared to monocultures. However, the surface expression levels in bMEC did not exhibit significant changes between co-culture and monoculture. Overall, our research indicates that the inflammatory response of bMEC is increased during co-culture with MNC, suggesting that the interaction between bMEC and MNC in the mammary gland amplifies the immune response to M. bovis in cows affected by M. bovis mastitis.

Selective IgG binding to the LPS glycolipid core found in bovine colostrum, or milk, during Escherichia coli mastitis influences endotoxin function

The dynamic interplay between intramammary IgG, formation of antigen-IgG complexes and effector immune cell function is essential for immune homeostasis within the bovine mammary gland. We explore how changes in the recognition and binding of anti-LPS IgG to the glycolipid "functional" core in milk from healthy or clinically diagnosed Escherichia coli (E. coli) mastitis cows' controls endotoxin function. In colostrum, we found a varied anti-LPS IgG repertoire and novel soluble LPS/IgG complexes with direct IgG binding to the LPS glycolipid core. These soluble complexes, absent in milk from healthy lactating cows, were evident in cows diagnosed with E. coli mastitis and correlated with endotoxin-driven inflammation. E. coli mastitis milk displayed a proportional reduction in anti-LPS glycolipid core IgG compared to colostrum. Milk IgG extracts showed that only colostrum IgG attenuated LPS induced endotoxin activity. Furthermore, LPS-stimulated reactive oxygen species (ROS) in milk granulocytes was only suppressed by colostrum IgG, while IgG extracts of neither colostrum nor E. coli mastitis milk influenced N-formylmethionine-leucyl-phenylalanine (fMLP)-stimulated ROS in LPS primed granulocytes. Our findings support bovine intramammary IgG diversity in health and in response to E. coli infection generate milk anti-LPS IgG repertoires that coordinate appropriate LPS innate-adaptive immune responses essential for animal health.

Bacteriophage-derived endolysins as innovative antimicrobials against bovine mastitis-causing streptococci and staphylococci: a state-of-the-art review

Bacteriophage-encoded endolysins, peptidoglycan hydrolases breaking down the Gram-positive bacterial cell wall, represent a groundbreaking class of novel antimicrobials to revolutionize the veterinary medicine field. Wild-type endolysins exhibit a modular structure, consisting of enzymatically active and cell wall-binding domains, that enable genetic engineering strategies for the creation of chimeric fusion proteins or so-called 'engineered endolysins'. This biotechnological approach has yielded variants with modified lytic spectrums, introducing new possibilities in antimicrobial development. However, the discovery of highly similar endolysins by different groups has occasionally resulted in the assignment of different names that complicate a straightforward comparison. The aim of this review was to perform a homology-based comparison of the wild-type and engineered endolysins that have been characterized in the context of bovine mastitis-causing streptococci and staphylococci, grouping homologous endolysins with ≥ 95.0% protein sequence similarity. Literature is explored by homologous groups for the wild-type endolysins, followed by a chronological examination of engineered endolysins according to their year of publication. This review concludes that the wild-type endolysins encountered persistent challenges in raw milk and in vivo settings, causing a notable shift in the field towards the engineering of endolysins. Lead candidates that display robust lytic activity are nowadays selected from screening assays that are performed under these challenging conditions, often utilizing advanced high-throughput protein engineering methods. Overall, these recent advancements suggest that endolysins will integrate into the antibiotic arsenal over the next decade, thereby innovating antimicrobial treatment against bovine mastitis-causing streptococci and staphylococci.

Different Immune Control of Gram-Positive and Gram-Negative Mammary Infections in Dairy Cows

In the dairy industry, bovine mastitis represents a major concern due to substantial production losses and costs related to therapies and early culling. The mechanisms of susceptibility and effective response to intra-mammary infections are still poorly understood. Therefore, we investigated innate immunity in acellular bovine skim milk through cytofluorimetric analyses of bacterial killing activity against both Gram-positive and Gram-negative pathogens. Freshly cultured E. coli and S. aureus strains were incubated with colostrum and milk samples at different lactation time points from two groups of cows, purportedly representing mastitis-resistant and mastitis-susceptible breeds; bacterial cells were analyzed for vitality by flow cytometry following incorporation of vital dyes. N-acetyl-β-D-glucosaminidase (NAGase) activity was also investigated in milk and colostrum samples. Our findings revealed that colostrum and milk bacterial killing activity was greater against S. aureus compared to E. coli., with this activity correlated with milk NAGase levels. Furthermore, both killing of S. aureus and NAGase activity were negatively correlated to the elapsed time of lactation. Interestingly, samples from the allegedly mastitis-resistant breed displayed higher bacterial killing and NAGase activities. Our study suggests that diverse control mechanisms are exerted against Gram-positive and Gram-negative pathogens in the mammary glands of cows, probably beyond those already described in the literature.

Reproducible isolation of bovine mammary macrophages for analysis of host pathogen interactions

BACKGROUND

Macrophages residing in milk are vital during intramammary infections. This study sought to develop a method enabling the investigation of macrophage responses to pathogens. Streptococcus uberis is the predominant cause of bovine mastitis UK-wide and its pathogenesis is unusual compared to other intramammary pathogens. Previous studies utilise macrophage cell lines, isolated bovine blood derived monocytes, or macrophages from raw milk through complex or inconsistent strategies such as fluorescence activated cell sorting (FACS), centrifugation and selective adherence, and CD14 antibody-microbeads. The centrifuge steps required in the initial stages often damage cells. Thus, the aim of this study was to develop a reliable, reproducible, and cost-effective method for isolating mammary macrophages from milk in a way that allows their culture, challenge with bacteria, and measurement of their response ex-vivo.

RESULTS

This method achieves an average yield of 1.27 × 107 cells per litre of milk. Whole milk with somatic cell range of 45-65 cells/µL produced excellent yields, with efficient isolations accomplished with up to 150 cells/µL. This strategy uses milk diluted in PAE buffer to enable low-speed centrifugation steps followed by seeding on tissue-culture-treated plastic. Seeding 1,000,000 milk-extracted cells onto tissue culture plates was sufficient to obtain 50,000 macrophage. Isolated macrophage remained responsive to challenge, with the highest concentration of IL-1β measured by ELISA at 20 h after challenge with S. uberis. In this model, the optimal multiplicity of infection was found to be 50:1 bacteria:macrophage. No difference in IL-1β production was found between macrophages challenged with live or heat-killed S. uberis. Standardisation of the production of IL-1β to that obtained following macrophage stimulation with LPS allowed for comparisons between preparations.

CONCLUSIONS

A cost-effective method, utilising low-speed centrifugation followed by adherence to plastic, was established to isolate bovine mammary macrophages from raw milk. This method was shown to be appropriate for bacterial challenge, therefore providing a cost-effective, ex-vivo, and non-invasive model of macrophage-pathogen interactions. The optimal multiplicity of infection for S. uberis challenge was demonstrated and a method for standardisation against LPS described which removes sample variation. This robust method enables, reproducible and reliable interrogation of critical pathogen-host interactions which occur in the mammary gland.

In vitro model of human mammary gland microbial colonization (MAGIC) demonstrates distinctive cytokine response to imbalanced human milk microbiota

Despite the established concept of the human mammary gland (MG) as a habitat with its own microbiota, the exact mechanism of MG colonization is still elusive and a well-characterized in vitro model would reinforce studies of the MG microbiota development. We aimed to establish and characterize an in vitro cell model for studying MAmmary Gland mIcrobial Colonization (MAGIC) model. We used the immortalized cell line MCF10A, which expresses the strong polarized phenotype similar to MG ductal epithelium when cultured on a permeable support (Transwell). We analyzed the surface properties of the MAGIC model by gene expression analysis of E-cadherin, tight junction proteins, and mucins and by scanning electron microscopy. To demonstrate the applicability of the model, we tested the adhesion capability of the whole human milk (HM) microbial community and the cellular response of the model when challenged directly with raw HM samples. MCF10A on permeable supports differentiated and formed a tight barrier, by upregulation of CLDN8, MUC1, MUC4, and MUC20 genes. The surface of the model was covered with mucins and morphologically diverse with at least two cell types and two types of microvilli. Cells in the MAGIC model withstood the challenge with heat-treated HM samples and responded differently to the imbalanced HM microbiota by distinctive cytokine response. The microbial profile of the bacteria adhered on the MAGIC model reflected the microbiological profile of the input HM samples. The well-studied MAGIC model could be useful for studies of bacterial attachment to the MG and for in vitro studies of biofilm formation and microbiota development.IMPORTANCEThe MAGIC model may be particularly useful for studies of bacterial attachment to the surface of the mammary ducts and for in vitro studies of biofilm formation and the development of the human mammary gland (MG) microbiota. The model is also useful for immunological studies of the interaction between bacteria and MG cells. We obtained pioneering information on which of the bacteria present in the raw human milk (HM) were able to attach to the epithelium treated directly with raw HM, as well as on the effects of bacteria on the MG epithelial cells. The MAGIC cell model also offers new opportunities for research in other areas of MG physiology, such as the effects of bioactive milk components on microbial colonization of the MG, mastitis prevention, and studies of probiotic development. Since resident MG bacteria may be an important factor in breast cancer development, the MAGIC in vitro tool also offers new opportunities for cancer research.

Bovine neutrophils stimulated with Streptococcus uberis induce neutrophil extracellular traps, and cause cytotoxicity and transcriptional upregulation of inflammatory cytokine genes in bovine mammary epithelial cells

This study aimed to understand the response of neutrophils stimulated by Streptococcus uberis, a major cause of mastitis. It was found that the production of neutrophil extracellular traps (NETs) was induced in milk clots from mastitic milk produced by S. uberis-infected bovine udders. The release of NETs from neutrophils stimulated by S. uberis was investigated. Bovine neutrophils cocultured with S. uberis in vitro released the components of NETs, which contained extracellular DNA and elastase. Bovine mammary epithelial cells (BMECs) incubated in coculture supernatants containing components of NETs, caused cytotoxicity and transcriptional upregulation of inflammatory cytokines, including of interleukin (IL) -1β, tumor necrosis factor (TNF)-α, IL-6, and IL-8, in BMECs. These findings suggest that bovine neutrophils stimulated by S. uberis induce responses that cause exacerbated inflammation, such as NET formation, cytotoxicity against BMECs, and increased production of inflammatory cytokines. Bovine neutrophil responses stimulated by S. uberis could be involved in the progression of S. uberis-induced mastitis.

Punch-excised explants of bovine mammary gland to model early immune response to infection

BACKGROUND

Mammary gland (MG) infections (mastitis) are frequent diseases of dairy cows that affect milk quality, animal welfare and farming profitability. These infections are commonly associated with the bacteria Escherichia coli and Staphylococcus aureus. Different in vitro models have been used to investigate the early response of the MG to bacteria, but the role of the teat in mastitis pathogenesis has received less attention. In this study, we used punch-excised teat tissue as an ex vivo model to study the immune mechanisms that arise early during infection when bacteria have entered the MG.

RESULTS

Cytotoxicity and microscopic analyses showed that bovine teat sinus explants have their morphology and viability preserved after 24 h of culture and respond to ex vivo stimulation with TLR-agonists and bacteria. LPS and E. coli trigger stronger inflammatory response in teat when compared to LTA and S. aureus, leading to a higher production of IL-6 and IL-8, as well as to an up-regulation of proinflammatory genes. We also demonstrated that our ex vivo model can be applied to frozen-stored explants.

CONCLUSIONS

In compliance with the 3Rs principle (replacement, reduction and refinement) in animal experimentation, ex vivo explant analyses proved to be a simple and affordable approach to study MG immune response to infection. This model, which better reproduces organ complexity than epithelial cell cultures or tissue slices, lends itself particularly well to studying the early phases of the MG immune response to infection.

Genetic polymorphisms in immune- and inflammation-associated genes and their association with bovine mastitis resistance/susceptibility

Bovine mastitis, the inflammation of the mammary gland, is a contagious disease characterized by chemical and physical changes in milk and pathological changes in udder tissues. Depressed immunity and higher expression of inflammatory cytokines with an elevated milk somatic cell count can be observed during mastitis in dairy cattle. The use of somatic cell count (SCC) and somatic cell score (SCS) as correlated traits in the indirect selection of animals against mastitis resistance is in progress globally. Traditional breeding for mastitis resistance seems difficult because of the low heritability (0.10-0.16) of SCC/SCS and clinical mastitis. Thus, genetic-marker-selective breeding to improve host genetics has attracted considerable attention worldwide. Moreover, genomic selection has been found to be an effective and fast method of screening for dairy cattle that are genetically resistant and susceptible to mastitis at a very early age. The current review discusses and summarizes the candidate gene approach using polymorphisms in immune- and inflammation-linked genes (CD4, CD14, CD46, TRAPPC9, JAK2, Tf, Lf, TLRs, CXCL8, CXCR1, CXCR2, C4A, C5, MASP2, MBL1, MBL2, LBP, NCF1, NCF4, MASP2, A2M, and CLU, etc.) and their related signaling pathways (Staphylococcus aureus infection signaling, Toll-like receptor signaling, NF-kappa B signaling pathway, Cytokine-cytokine receptor, and Complement and coagulation cascades, etc.) associated with mastitis resistance and susceptibility phenotypic traits (IL-6, interferon-gamma (IFN-γ), IL17, IL8, SCS, and SCC) in dairy cattle.

Immune profiling of experimental murine mastitis reveals conserved response to mammary pathogenic Escherichia coli, Mycoplasma bovis, and Streptococcus uberis

Mastitis is one of the most prevalent and economically important diseases of dairy animals. The disease is caused by ascending bacterial infection through the teat canal. Among the most common mastitis-causing bacteria are Gram-negative coliforms, Gram-positive streptococci and staphylococci, and mycoplasma. The most prominent cellular hallmark of acute mammary infection is a massive recruitment of blood neutrophils into the tubular and alveolar milk spaces. The complex biological processes of leukocyte recruitment, activation, adhesion, and migration in the mammary gland remain largely elusive to date. While field research of mastitis in dairy animals contributed a lot to the development of mitigation, control, and even eradication programs, little progress was made toward understanding the molecular mechanisms underlying the pathogenesis of the disease. We report here experimental mastitis model systems in lactating mice challenged with field strains of common udder pathogens in dairy cows. We used these model systems to apply recently developed multiplex gene expression technology (Nanostring nCounter), which enabled us to study the expression of over 700 immune genes. Our analysis revealed a core of 100 genes that are similarly regulated and functionally or physically interacting in E. coli, M. bovis, and Strep uberis murine mastitis. Common significantly enriched gene sets include TNFɑ signaling via NFkB, Interferon gamma and alpha response, and IL6-JAK-STAT3 signaling. In addition, we show a significantly enriched expression of genes associated with neutrophil extracellular traps (NET) in glands challenged by the three pathogens. Ligand-receptor analysis revealed interactions shared by the three pathogens, including the interaction of the cytokines IL1β, IL1ɑ, and TNFɑ with their receptors, and proteins involved in immune cell recruitment such as complement C3 and ICAM1 (with CD11b), chemokines CCL3 and CCL4 (with CCR1), and CSF3 (with CSF3R). Taken together, our results show that mammary infection with E. coli, M. bovis, and Strep uberis culminated in the activation of a conserved core of immune genes and pathways including NET formation.