Two functionally distinct myeloid dendritic cell subpopulations are present in bovine blood

Simplified Approaches for the Production of Monocyte-Derived Dendritic Cells and Study of Antigen Presentation in Bovine

Dendritic cells are sentinels of the immune system responsible for the initiation of adaptive immune mechanisms. In that respect, the study of these cells is essential for a full understanding of host response to infectious agents and vaccines. In ruminants, the large blood volume facilitates the isolation of abundant monocytes and their derivation to other antigen-presenting cells such as dendritic cells and macrophages. However, the available protocols for the production of bovine monocyte-derived dendritic cells (moDCs) rely mostly on time-consuming and costly techniques such as density gradient centrifugation and magnetic sorting of cells. In this study, we describe a simplified protocol for the production of bovine moDC using conventional and serum-free media. We also employ moDC produced by this approach to carry out a flow cytometry-based antigen presentation assay adapted to blood fresh or frozen cells. The experimental strategies described here might enable the setup of studies involving a large number of individuals, requiring a large number of dendritic cells, or relying on the utilization of cryopreserved blood cells. These simplified protocols might contribute to the elucidation of cell-mediated immune responses in bovine.

Adrenergic receptor gene expression in bovine leukocytes

The α- and β-adrenergic receptors (ARs) bind the stress hormones epinephrine (E), norepinephrine (NE), and dopamine and activate diverse physiological responses. A lack of information on AR gene expression in leukocytes limits our understanding of how stress alters immune function. Quantitative analyses of AR gene expression was completed for bovine leukocytes. Individual leukocyte lineages and subpopulations within lineages were isolated with high-speed cell sorting to facilitate a targeted analysis of AR gene expression. These analyses confirmed all 9 AR genes were expressed in bovine leukocytes with marked differences in AR gene expression when comparing among leukocyte lineages. Furthermore, separation of polymorphonuclear cells into neutrophils and eosinophils revealed these key innate immune cells also differ significantly in AR gene expression. This study provides the first comprehensive survey of AR gene expression in immune cells of any mammalian species and provides insight into conflicting reports that stress can either activate or suppress immune function.

Bovine Adenovirus-3 Tropism for Bovine Leukocyte Sub-Populations

A number of characteristics including lack of virulence and the ability to grow to high titers, have made bovine adenovirus-3 (BAdV-3) a vector of choice for further development as a vaccine-delivery vehicle for cattle. Despite the importance of blood leukocytes, including dendritic cells (DC), in the induction of protective immune responses, little is known about the interaction between BAdV-3 and bovine blood leukocytes. Here, we demonstrate that compared to other leukocytes, bovine blood monocytes and neutrophils are significantly transduced by BAdV404a (BAdV-3, expressing enhanced yellow green fluorescent protein [EYFP]) at a MOI of 1-5 without a significant difference in the mean fluorescence of EYFP expression. Moreover, though expression of some BAdV-3-specific proteins was observed, no progeny virions were detected in the transduced monocytes or neutrophils. Interestingly, addition of the "RGD" motif at the C-terminus of BAdV-3 minor capsid protein pIX (BAV888) enhanced the ability of the virus to enter the monocytes without altering the tropism of BAdV-3. The increased uptake of BAV888 by monocytes was associated with a significant increase in viral genome copies and the abundance of EYFP and BAdV-3 19K transcripts compared to BAdV404a-transduced monocytes. Our results suggest that BAdV-3 efficiently transduces monocytes and neutrophils in the absence of viral replication. Moreover, RGD-modified capsid significantly increases vector uptake without affecting the initial interaction with monocytes.

The degree of postpartum metabolic challenge in dairy cows is associated with peripheral blood mononuclear cell transcriptome changes of the innate immune system

Dairy cows undergo a nutrient deficit immediately postpartum when lactational demands exceed nutrient intake. This occurs concurrently to an increased challenge due to bacterial and viral infections, yet ability for pathogen clearance is reduced despite a heightened and often host-damaging inflammatory response. We hypothesized that nutrient stress is associated with differences in the immune cell transcriptome. Our objective was therefore to investigate differentially expressed pathways (DEP) by RNA-seq in peripheral blood mononuclear cells harvested 3 weeks before and 1 week after calving from Holstein cows in low (L, n = 3) or high (H, n = 3) postpartum metabolic stress situations. Metabolic stress was defined by differences in circulating concentrations of glucose, fatty acids, and ketones postpartum. Cows in group H showed several upregulated DEP in relation to myeloid cell function and inflammatory response, as well as downregulation of the Th2 pathway. Principal components analysis showed that the transcriptome of group H postpartum samples was most different from all other samples. Differences in DE genes were noted even prepartum albeit fewer DE genes were identified and myeloid cell pathways in group H were generally downregulated at this time compared with group L. Samples within group L showed little difference between the two time points. We conclude that the metabolic phenotype of cows allowed us to identify differences in immune-regulatory pathways and that myeloid immune cells could play a dominant role in identifying these metabolically-associated differences that were demonstrated among a mixed mononuclear cell population.

Precise Delineation and Transcriptional Characterization of Bovine Blood Dendritic-Cell and Monocyte Subsets

A clear-cut delineation of bovine bona fide dendritic cells (DC) from monocytes has proved challenging, given the high phenotypic and functional plasticity of these innate immune cells and the marked phenotypic differences between species. Here, we demonstrate that, based on expression of Flt3, CD172a, CD13, and CD4, a precise identification of bovine blood conventional DC type 1 and 2 (cDC1, cDC2), plasmacytoid DC (pDC), and monocytes is possible with cDC1 being Flt3⁺CD172a^dimCD13⁺CD4⁻, cDC2 being Flt3⁺CD172a⁺CD13⁻CD4⁻, pDC being Flt3⁺CD172a^dimCD13⁻CD4⁺, and monocytes being Flt3⁻CD172a^highCD13⁻CD4⁻. The phenotype of these subsets was characterized in further detail, and a subset-specific differential expression of CD2, CD5, CD11b, CD11c, CD14, CD16, CD26, CD62L, CD71, CD163, and CD205 was found. Subset identity was confirmed by transcriptomic analysis and subset-specific transcription of conserved key genes. We also sorted monocyte subsets based on their differential expression of CD14 and CD16. Classical monocytes (CD14⁺CD16⁻) clustered clearly apart from the two CD16⁺ monocyte subsets probably representing intermediate and non-classical monocytes described in human. The transcriptomic data also revealed differential gene transcription for molecules involved in antigen presentation, pathogen sensing, and migration, and therefore gives insights into functional differences between bovine DC and monocyte subsets. The identification of cell-type- and subset-specific gene transcription will assist in the quest for “marker molecules” that—when targeted by flow cytometry—will greatly facilitate research on bovine DC and monocytes. Overall, species comparisons will elucidate basic principles of DC and monocyte biology and will help to translate experimental findings from one species to another.

Phenotypic and functional analysis of bovine peripheral blood dendritic cells before parturition by a novel purification method

Dendritic cells (DCs) are specialized antigen presenting cells specializing in antigen uptake and processing, and play an important role in the innate and adaptive immune response. A subset of bovine peripheral blood DCs was identified as CD172a⁺/CD11c⁺/MHC (major histocompatibility complex) class II⁺ cells. Although DCs are identified at 0.1%–0.7% of peripheral blood mononuclear cells (PBMC), the phenotype and function of DCs remain poorly understood with regard to maintaining tolerance during the pregnancy. All cattle used in this study were 1 month before parturition. We have established a novel method for the purification of DCs from PBMC using magnetic‐activated cell sorting, and purified the CD172a⁺/CD11c⁺DCs, with high expression of MHC class II and CD40, at 84.8% purity. There were individual differences in the expressions of CD205 and co‐stimulatory molecules CD80 and CD86 on DCs. There were positive correlations between expression of cytokine and co‐stimulatory molecules in DCs, and the DCs maintained their immune tolerance, evidenced by their low expressions of the co‐stimulatory molecules and cytokine production. These results suggest that before parturition a half of DCs may be immature and tend to maintain tolerance based on the low cytokine production, and the other DCs with high co‐stimulatory molecules may already have the ability of modulating the T‐cell linage.

CD335 (NKp46)+ T-Cell Recruitment to the Bovine Upper Respiratory Tract during a Primary Bovine Herpesvirus-1 Infection

Bovine natural killer (NK) cells were originally defined by the NK activation receptor CD335 [natural killer cell p46-related protein (NKp46)], but following the discovery of NKp46 expression on human T-cells, the definition of conventional bovine NK cells was modified to CD335⁺CD3⁻ cells. Recently, a bovine T-cell population co-expressing CD335 was identified and these non-conventional T-cells were shown to produce interferon (IFN)-γ and share functional properties with both conventional NK cells and T-cells. It is not known, however, if CD335⁺ bovine T-cells are recruited to mucosal surfaces and what chemokines play a role in recruiting this unique T-cell subpopulation. In this study, bovine herpesvirus-1 (BHV-1), which is closely related to herpes simplex virus-1, was used to investigate bovine lymphocyte cell populations recruited to the upper respiratory tract following a primary respiratory infection. Immunohistochemical staining with individual monoclonal antibodies revealed significant (P < 0.05) recruitment of CD335⁺, CD3⁺, and CD8⁺ lymphocyte populations to the nasal turbinates on day 5 following primary BHV-1 infection. Dual-color immunofluorescence revealed that cells recruited to nasal turbinates were primarily T-cells that co-expressed both CD335 and CD8. This non-conventional T-cell population represented 77.5% of CD355⁺ cells and 89.5% of CD8⁺ cells recruited to nasal turbinates on day 5 post-BHV-1 infection. However, due to diffuse IFN-γ staining of nasal turbinate tissue, it was not possible to directly link increased IFN-γ production following BHV-1 infection with the recruitment of non-conventional T-cells. Transcriptional analysis revealed CCL4, CCL5, and CXCL9 gene expression was significantly (P < 0.05) upregulated in nasal turbinate tissue following BHV-1 infection. Therefore, no single chemokine was associated with recruitment of non-conventional T-cells. In conclusion, the specific recruitment of CD335⁺ and CD8⁺ non-conventional T-cells to viral-infected tissue suggests that these cells may play an important role in either the clearance of a primary BHV-1 infection or regulating host responses during viral infection. The early recruitment of non-conventional T-cells following a primary viral infection may enable the host to recognize viral-infected cells through NKp46 while retaining the possibility of establishing T-cell immune memory.

Molecular vaccine prepared by fusion of XCL1 to the multi-epitope protein of foot-and-mouth disease virus enhances the specific humoural immune response in cattle

Targeting antigen to dendritic cells (DCs) is a promising way to manipulate the immune response and to design prophylactic molecular vaccines. In this study, the cattle XCL1, ligand of XCR1, was fused to the type O foot-and-mouth disease virus (FMDV) multi-epitope protein (XCL-OB7) to create a molecular vaccine antigen, and an ^△XCL-OB7 protein with a mutation in XCL1 was used as the control. XCL-OB7 protein specifically bound to the XCR1 receptor, as detected by flow cytometry. Cattle vaccinated with XCL-OB7 showed a significantly higher antibody response than that to the ^△XCL-OB7 control (P < 0.05). In contrast, when XCL-OB7 was incorporated with poly (I:C) to prepare the vaccine, the antibody response of the immunized cattle was significantly decreased in this group and was lower than that in the ^△XCL-OB7 plus poly (I:C) group. The FMDV challenge indicated that cattle immunized with the XCL-OB7 alone or the ^△XCL-OB7 plus poly (I:C) obtained an 80% (4/5) clinical protective rate. However, cattle vaccinated with ^△XCL-OB7 plus poly (I:C) showed more effective inhibition of virus replication than that in the XCL-OB7 group after viral challenge, according to the presence of antibodies against FMDV non-structural protein 3B. This is the first test of DC-targeted vaccines in veterinary medicine to use XCL1 fused to FMDV antigens. This primary result showed that an XCL1-based molecular vaccine enhanced the antibody response in cattle. This knowledge should be valuable for the development of antibody-dependent vaccines for some infectious diseases in cattle.

Induction of interferon and interferon-induced antiviral effector genes following a primary bovine herpesvirus-1 (BHV-1) respiratory infection

Invitro investigations have identified a variety of mechanisms by which herpesviruses evade interferon-stimulated antiviral effector mechanisms. However, these immune evasion mechanisms have not been evaluated during a bovine herpesvirus-1 (BHV-1) infection. This study investigated the transcription and secretion of type I and II interferons (IFNs) and the transcription of IFN-stimulated genes (ISGs) during a primary BHV-1 infection of the upper respiratory tract (URT) in naïve calves. IFN-α, -β and -γ transcription in nasal turbinates and protein levels in nasal secretions increased following infection. Increased IFN type I and II secretion was detected 3 days post-infection (p.i.) and IFN production increased in parallel with virus shedding. Expression of ISGs, including Mx1, OAS and BST-2, also increased significantly (P<0.05) in nasal turbinates on day 3 p.i. and elevated ISG expression persisted throughout the period of viral shedding. In contrast, RNAase L gene expression was not induced during the BHV-1 infection in the nasal turbinates, but was induced on day 10 p.i. in the trachea. In vitro studies confirmed that recombinant bovine (rBo)IFN-α, -β and -γ induced expression of Mx1, OAS and BST-2, but decreased RNAse L transcript in bovine epithelial cells. Relative to vesicular stomatitisvirus (VSV), BHV-1 was resistant to the antiviral activity of rBoIFN-α and -γ, but treatment of epithelial cells with 10 ng rBoIFN-β ml-1 effected an 80 % inhibition of BHV-1 replication and complete inhibition of VSV replication. These observations confirm that the transcription and translation of type I and II IFNs increase during BHV-1 infection, while the transcription of some ISGs is not inhibited.

The Identification and Distribution of Cattle XCR1 and XCL1 among Peripheral Blood Cells: New Insights into the Design of Dendritic Cells Targeted Veterinary Vaccine

The chemokine (C motif) receptor 1 (XCR1) and its ligandXCL1 have been intensively studied in the mouse and human immune systems. Here, we determined the molecular characteristics of cattle XCR1 and XCL1 and their distribution among peripheral blood cells. Cattle XCR1 mRNA expression was mainly restricted to CD26+CADM1+CD205+MHCII+CD11b- cells in blood that were otherwise lineage marker negative (lin-); these represented a subset of classic dendritic cells (DCs), not plasmacytoid DCs. Some of these DCs expressed CD11a, CD44, CD80 and CD86, but they did not express CD4, CD8, CD163 or CD172a. Cattle XCL1 was expressed in quiescent NK cells and in activated CD8+ T cells. Cattle XCR1+ DCs migrated chemotactically in response to mouse, but not to human, XCL1. The distribution characters of cattle XCR1 and XCL1 suggested a vital role in regulation of acquired immune responses and indicated a potential for a DC targeted veterinary vaccine in cattle using XCL1 fused antigens.

Phenotype and Function of CD209+ Bovine Blood Dendritic Cells, Monocyte-Derived-Dendritic Cells and Monocyte-Derived Macrophages

Phylogenic comparisons of the mononuclear phagocyte system (MPS) of humans and mice demonstrate phenotypic divergence of dendritic cell (DC) subsets that play similar roles in innate and adaptive immunity. Although differing in phenotype, DC can be classified into four groups according to ontogeny and function: conventional DC (cDC1 and cDC2), plasmacytoid DC (pDC), and monocyte derived DC (MoDC). DC of Artiodactyla (pigs and ruminants) can also be sub-classified using this system, allowing direct functional and phenotypic comparison of MoDC and other DC subsets trafficking in blood (bDC). Because of the high volume of blood collections required to study DC, cattle offer the best opportunity to further our understanding of bDC and MoDC function in an outbred large animal species. As reported here, phenotyping DC using a monoclonal antibody (mAb) to CD209 revealed CD209 is expressed on the major myeloid population of DC present in blood and MoDC, providing a phenotypic link between these two subsets. Additionally, the present study demonstrates that CD209 is also expressed on monocyte derived macrophages (MoΦ). Functional analysis revealed each of these populations can take up and process antigens (Ags), present them to CD4 and CD8 T cells, and elicit a T-cell recall response. Thus, bDC, MoDC, and MoΦ pulsed with pathogens or candidate vaccine antigens can be used to study factors that modulate DC-driven T-cell priming and differentiation ex vivo.

Bovine Viral Diarrhea Virus Infects Monocyte-Derived Bovine Dendritic Cells by an E2-Glycoprotein-Mediated Mechanism and Transiently Impairs Antigen Presentation

Infection of professional antigen presenting cells by viruses can have a marked effect on these cells and important consequences for the generation of subsequent immune responses. In this study, we demonstrate that different strains of bovine viral diarrhea virus (BVDV) infect bovine dendritic cells differentiated from nonadherent peripheral monocytes (moDCs). BVDV did not cause apoptosis in these cells. Infection of moDC was prevented by incubating the virus with anti-E2 antibodies or by pretreating the cells with recombinant E2 protein before BVDV contact, suggesting that BVDV infects moDC through an E2-mediated mechanism. Virus entry was not reduced by incubating moDC with Mannan or ethylenediaminetetraacetic acid (EDTA) before infection, suggesting that Ca(2+) and mannose receptor-dependent pathways are not mediating BVDV entry to moDC. Infected moDC did not completely upregulate maturation surface markers. Infection, but not treatment with inactivated virus, prevented moDC to present a third-party antigen to primed CD4(+) T cells within the first 24 hours postinfection (hpi). Antigen-presenting capacity was recovered when viral replication diminished at 48 hpi, suggesting that active infection may interfere with moDC maturation. Altogether, our results suggest an important role of infected DCs in BVDV-induced immunopathogenesis.

Effect of Foot-and-Mouth Disease Virus Infection on the Frequency, Phenotype and Function of Circulating Dendritic Cells in Cattle

Foot-and-mouth disease virus (FMDV) is a highly contagious virus that causes one of the most devastating diseases in cloven-hoofed animals. Disease symptoms develop within 2 to 3 days of exposure and include fever and vesicular lesions on the tongue and hooves. Dendritic cells (DC) play an essential role in protective immune responses against pathogens. Therefore, investigating their role during FMDV infection would lead to a better understanding of host-pathogen interactions. In this study, following infection of cattle with FMDV, we investigated the frequency and function of conventional (cDC) and plasmacytoid DC (pDC) in blood by using multi-color flow cytometry. We show that the frequency of cDC and pDC increased following FMDV infection and peaked 3 to 4 days post-infection. During peak viremia, the cattle became lymphopenic, the expression of MHC class II molecules on cDC and pDC was dramatically down-regulated, the processing of exogenous antigen by cDC and pDC was impaired, and there was an increase in IL-10 production by DC and monocytes. Notably, after clearance of FMDV from the blood, MHC class II expression returned to pre-infection levels. Altogether, our study demonstrates that in cattle, FMDV inhibits the function of DC, thereby retarding the initiation of adaptive immune responses, potentially enhancing virus shedding during the acute phase of infection.

Bacterial Ghosts of Escherichia coli Drive Efficient Maturation of Bovine Monocyte-Derived Dendritic Cells

Bacterial ghosts (BGs) are empty cell envelopes derived from Gram-negative bacteria. They not only represent a potential platform for development of novel vaccines but also provide a tool for efficient adjuvant and antigen delivery system. In the present study, we investigated the interaction between BGs of Escherichia coli (E. coli) and bovine monocyte-derived dendritic cells (MoDCs). MoDCs are highly potent antigen-presenting cells and have the potential to act as a powerful tool for manipulating the immune system. We generated bovine MoDCs in vitro from blood monocytes using E. coli expressed bovine GM-CSF and IL-4 cytokines. These MoDCs displayed typical morphology and functions similar to DCs. We further investigated the E. coli BGs to induce maturation of bovine MoDCs in comparison to E. coli lipopolysaccharide (LPS). We observed the maturation marker molecules such as MHC-II, CD80 and CD86 were induced early and at higher levels in BG stimulated MoDCs as compared to the LPS stimulated MoDCs. BG mediated stimulation induced significantly higher levels of cytokine expression in bovine MoDCs than LPS. Both pro-inflammatory (IL-12 and TNF-α) and anti-inflammatory (IL-10) cytokines were induced in MoDCs after BGs stimulation. We further analysed the effects of BGs on the bovine MoDCs in an allogenic mixed lymphocyte reaction (MLR). We found the BG-treated bovine MoDCs had significantly (p<0.05) higher capacity to stimulate allogenic T cell proliferation in MLR as compared to the LPS. Taken together, these findings demonstrate the E. coli BGs induce a strong activation and maturation of bovine MoDCs.

Tissue- and age-dependent expression of the bovine DEFB103 gene and protein

Beta-defensin 103 (DEFB103) shares little homology with 8 other members of the bovine beta-defensin family and in other species DEFB103 protein has diverse functions, including antimicrobial activity, a chemoattractant for dendritic cells, enhancing epithelial wound repair and regulating hair colour. Expression of the bovine DEFB103 gene was surveyed in 27 tissues and transcript was most abundant in tissues with stratified squamous epithelium. Oral cavity epithelial tissues and nictitating membrane consistently expressed high levels of DEFB103 gene transcript. An age-dependent decrease (P < 0.05) in DEFB103 gene expression was only observed for buccal epithelium when comparing healthy 10- to 14-day-old and 10- to 12-month-old calves. A bovine herpesvirus-1 respiratory infection did, however, significantly (P < 0.05) up-regulate DEFB103 gene expression in the buccal epithelium of 6- to 8-month-old calves. Finally, DEFB103 transcript was low in lymph nodes draining the skin and at the limit of detection in other internal organs such as lung, intestine and kidney. Affinity-purified rabbit antisera to bovine DEFB103 was used to identify cells expressing DEFB103 protein within tissues with stratified squamous epitheliums. DEFB103 protein was most abundant in basal epithelial cells and was present in these cells prior to birth. Beta-defensins have been identified as regulators of dendritic cell (DC) chemokine responses and we observed a close association between DCs and epithelial cells expressing DEFB103 in both the fetus and newborn calf. In conclusion, bovine DEFB103 gene expression is most abundant in stratified squamous epithelium with DEFB103 protein localised to basal epithelial cells. These observations are consistent with proposed roles for DEFB103 in DC recruitment and repair of stratified squamous epithelium.

Development and characterization of a monoclonal antibody specific for bovine CD209

Dendritic cells (DC) play a central role in tailoring the immune response to pathogens. Effector activity is mediated through pattern recognition receptors (PRRs) that recognize pathogen associated molecular patterns (PAMPS). C-type lectin receptors (CLR) comprise a group of PRRs that recognize a broad range of pathogens. CD209 (DC-specific ICAM3-grabbing non-integrin, DC-SIGN) is a CLR expressed on DC that plays a critical role on DC function and pathogen recognition. It facilitates DC migration to peripheral tissues and local lymph nodes and mediates T cell activation by binding ICAM-2 (CD102) and ICAM-3 (CD50). The absence of monoclonal antibody (mAb) to bovine CD209 has limited the ability to characterize the phenotype and function of DC in cattle. To address this issue we developed and used a mAb to CD209 to characterize the phenotype of CD209 expressing cells in bovine blood using flow cytometry. Initial analysis has revealed the CD209 positive population in blood is comprised of multiple phenotypically defined subsets.

Stress, acute phase proteins and immune modulation in calves

Acute phase and inflammatory responses are triggered by a variety of intrinsic and extrinsic stressors that come at a cost through suppressing the normal function of tissues and organs of domestic animals. Recently, with growing attention placed on global warming and animal welfare, there has been an increased interest in improving our understanding of the relationships between different classes of stress, the expression of acute phase proteins (APPs), the stress-related endocrine system and immunomodulation. Immune function is compromised by all forms of stress including poor nutrition, weaning, extreme thermal conditions, injury and infection in calves. Proinflammatory cytokines, APPs and hormones of the hypothalamic–pituitary adrenal axis as well as the composition of immune cells can all be characterised in culture supernatants and peripheral blood. APPs have been used as biomarkers for the stress status of ruminants both experimentally and in field studies. Therefore detailed studies of the mechanisms of action of these APPs and their interactions in ameliorating different stress responses are warranted. The focus of this review is on the aetiology of the responses in calves under severe stress and its impact on growth and immune status. Possible strategies to alleviate this condition including the role of specific feed additives are presented.