Isolation and characterization of macrophages from a mixed primary culture of bovine liver cells

Isolation and propagation of bovine blood-derived macrophages using a mixed culture with bovine endothelial B46 cells

Macrophages are innate immune cells with multiple functions such as phagocytosis, cytokine production, and antigen presentation. Since macrophages play critical roles in some bacterial infectious diseases in cattle, including tuberculosis, paratuberculosis, and brucellosis, the in vitro culturing of bovine macrophages is useful for evaluating host-pathogen interactions at the cellular and molecular levels. We have previously reported the establishment of two immortalized bovine liver sinusoidal cell lines, endothelial B46 cells and myofibroblast-like A26 cells (Cell Biology International, 40, 1372-1379, 2016). In this study, we investigated the use of these cell lines as feeder cells that support the proliferation of bovine blood-derived macrophages (BBMs). Notably, the B46 cell line efficiently acts as feeder cells for the propagation of BBMs. Compared with primary cultured vascular endothelial cells, the infinite proliferation ability of B46 cells is more beneficial for preparing confluent feeder layers. In conclusion, this study provides a simple and efficient protocol for the isolation and propagation of BBMs using a primary mixed culture of bovine whole blood with B46 feeder cells. Isolated BBMs are expected to be useful for developing in vitro models for studying the interactions between bovine pathogens and host immune cells.

Developmental Changes of Duckling Liver and Isolation of Primary Hepatocytes

The liver is the main site of fat synthesis and plays an important role in the study of fat deposition in poultry. In this study, we investigated the developmental changes of duckling livers and isolated primary duck hepatocytes. Firstly, we observed morphological changes in duckling livers from the embryonic period to the first week after hatching. Liver weight increased with age. Hematoxylin-eosin and Oil Red O staining analyses showed that hepatic lipids increased gradually during the embryonic period and declined post-hatching. Liver samples were collected from 21-day-old duck embryos for hepatocyte isolation. The hepatocytes showed limited self-renewal and proliferative ability and were maintained in culture for up to 7 days. Typical parenchymal morphology, with a characteristic polygonal shape, appeared after two days of culture. Periodic acid-Schiff (PAS) staining analysis confirmed the characteristics of duck embryo hepatocytes. PCR analysis showed that these cells from duck embryos expressed the liver cell markers ALB and CD36. Immunohistochemical staining and immunofluorescence analysis also confirmed ALB and CK18 expression. Our findings provide a novel insight regarding in vitro cell culture and the characteristics of hepatocytes from avian species, which could enable further studies concerning specific research on duck lipid metabolism.

Genome-wide association analysis identified both RNA-seq and DNA variants associated to paratuberculosis in Canadian Holstein cattle 'in vitro' experimentally infected macrophages

Background

Mycobacterium avium ssp. paratuberculosis (MAP) is the causative agent of paratuberculosis, or Johne’s disease (JD), an incurable bovine disease. The evidence for susceptibility to MAP disease points to multiple interacting factors, including the genetic predisposition to a dysregulation of the immune system. The endemic situation in cattle populations can be in part explained by a genetic susceptibility to MAP infection. In order to identify the best genetic improvement strategy that will lead to a significant reduction of JD in the population, we need to understand the link between genetic variability and the biological systems that MAP targets in its assault to dominate macrophages. MAP survives in macrophages where it disseminates. We used next-generation RNA (RNA-Seq) sequencing to study of the transcriptome in response to MAP infection of the macrophages from cows that have been naturally infected and identified as positive for JD (JD (+); n = 22) or negative for JD (healthy/resistant, JD (−); n = 28). In addition to identifying genetic variants from RNA-seq data, SNP variants were also identified using the Bovine SNP50 DNA chip.

Results

The complementary strategy allowed the identification of 1,356,248 genetic variants, including 814,168 RNA-seq and 591,220 DNA chip variants. Annotation using SnpEff predicted that the 2435 RNA-seq genetic variants would produce high functional effect on known genes in comparison to the 33 DNA chip variants. Significant variants from JD(+/−) macrophages were identified by genome-wide association study and revealed two quantitative traits loci: BTA4 and 11 at (P < 5 × 10^− 7). Using BovineMine, gene expression levels together with significant genomic variants revealed pathways that potentially influence JD susceptibility, notably the energy-dependent regulation of mTOR by LKB1-AMPK and the metabolism of lipids.

Conclusion

In the present study, we succeeded in identifying genetic variants in regulatory pathways of the macrophages that may affect the susceptibility of cows that are healthy/resistant to MAP infection. RNA-seq provides an unprecedented opportunity to investigate gene expression and to link the genetic variations to biological pathways that MAP normally manipulate during the process of killing macrophages. A strategy incorporating functional markers into genetic selection may have a considerable impact in improving resistance to an incurable disease. Integrating the findings of this research into the conventional genetic selection program may allow faster and more lasting improvement in resistance to bovine paratuberculosis in dairy cattle.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-07487-4.

Transcriptome Profiling of Bovine Macrophages Infected by Mycobacterium avium spp. paratuberculosis Depicts Foam Cell and Innate Immune Tolerance Phenotypes

Mycobacterium avium spp. paratuberculosis (MAP) is the causative agent of Johne's disease (JD), also known as paratuberculosis, in ruminants. The mechanisms of JD pathogenesis are not fully understood, but it is known that MAP subverts the host immune system by using macrophages as its primary reservoir. MAP infection in macrophages is often studied in healthy cows or experimentally infected calves, but reports on macrophages from naturally infected cows are lacking. In our study, primary monocyte-derived macrophages (MDMs) from cows diagnosed as positive (+) or negative (–) for JD were challenged in vitro with live MAP. Analysis using next-generation RNA sequencing revealed that macrophages from JD(+) cows did not present a definite pattern of response to MAP infection. Interestingly, a considerable number of genes, up to 1436, were differentially expressed in JD(–) macrophages. The signatures of the infection time course of 1, 4, 8, and 24 h revealed differential expression of ARG2, COL1A1, CCL2, CSF3, IL1A, IL6, IL10, PTGS2, PTX3, SOCS3, TNF, and TNFAIP6 among other genes, with major effects on host signaling pathways. While several immune pathways were affected by MAP, other pathways related to hepatic fibrosis/hepatic stellate cell activation, lipid homeostasis, such as LXR/RXR (liver X receptor/retinoid X receptor) activation pathways, and autoimmune diseases (rheumatoid arthritis or atherosclerosis) also responded to the presence of live MAP. Comparison of the profiles of the unchallenged MDMs from JD(+) vs. JD(–) cows showed that 868 genes were differentially expressed, suggesting that these genes were already affected before monocytes differentiated into macrophages. The downregulated genes predominantly modified the general cell metabolism by downregulating amino acid synthesis and affecting cholesterol biosynthesis and other energy production pathways while introducing a pro-fibrotic pattern associated with foam cells. The upregulated genes indicated that lipid homeostasis was already supporting fat storage in uninfected JD(+) MDMs. For JD(+) MDMs, differential gene expression expounds long-term mechanisms established during disease progression of paratuberculosis. Therefore, MAP could further promote disease persistence by influencing long-term macrophage behavior by using both tolerance and fat-storage states. This report contributes to a better understanding of MAP's controls over the immune cell response and mechanisms of MAP survival.

Bovine WC1+ and WC1neg γδ T Lymphocytes Influence Monocyte Differentiation and Monocyte-Derived Dendritic Cell Maturation during In Vitro Mycobacterium avium Subspecies paratuberculosis Infection

During early Mycobacterium avium subspecies paratuberculosis (Map) infection, complex interactions occur between the bacteria, cells from the mononuclear phagocyte system (MPS) including both resident (macrophages and dendritic cells) and recruited (monocytes) cells, and other mucosal sentinel cells such as γδ T lymphocytes. Though the details of early host–pathogen interactions in cattle remain largely underexplored, our hypothesis is that these significantly influence development of host immunity and ultimate success or failure of the host to respond to Map infection. The aims of the present study were to first characterize monocyte-derived MPS cells from young calves with respect to their immunophenotype and function. Then, we set out to investigate the effects of WC1⁺ and WC1^neg γδ T lymphocytes on (1) the differentiation of autologous monocytes and (2) the maturation of autologous monocyte-derived dendritic cells (MDDCs). To achieve this, peripheral blood WC1⁺ or WC1^neg γδ T lymphocytes were cocultured with either autologous freshly isolated peripheral blood-derived monocytes or autologous immature MDDCs (iMDDCs). We began by measuring several markers of interest on MPS cells. Useful markers to distinguish monocyte-derived macrophages (MDMs) from MDDCs include CD11b, CD163, and CD172a, which are expressed significantly higher on MDMs compared with MDDCs. Function, but not phenotype, was influenced by WC1^neg γδ T lymphocytes: viability of Map harvested from monocytes differentiated in the presence of WC1^neg γδ T lymphocytes (dMonWC1^neg) was significantly lower compared to MDMs and MDDCs. With respect to DC maturation, we first showed that mature MDDCs (mMDDCs) have significantly higher expression of CD11c, CD80, and CD86 compared with iMDDCs, and the phagocytic capacity of mMDDCs is significantly reduced compared to iMDDCs. We then showed that γδ T lymphocyte subsets induce functional (reduced phagocytosis) but not phenotypic (surface marker expression) iMDDC maturation. These data collectively show that γδ T lymphocytes influence differentiation, maturation, and ultimately the function of monocytes during Map infection, which has significant implications on survival of Map and success of host defense during early Map infection.

Establishment of SV40 large T antigen-immortalized bovine liver sinusoidal cell lines and their immunological responses to deoxynivalenol and lipopolysaccharide

Immortalized bovine sinusoidal cell lines provide useful tools to study the immunological responses in the liver to the gastrointestinal tract-derived toxic substances, which may cause systemic symptoms in the affected livestock. Here, we established two immortalized bovine liver sinusoidal cell lines, endothelial-like B46, and myofibroblast-like A26, from primary cultures of bovine liver cells by the transfection with SV40 large T antigen. The pro-inflammatory cytokine responses in these cell lines to deoxynivalenol (DON) and lipopolysaccharide (LPS) were then compared to those in the primary bovine Kupffer cells (BKC). BKC were highly responsive to LPS, showing increased levels of IL-1α, IL-1β, IL-6, and TNF-α mRNA 3 h after stimulation. DON induced similar pro-inflammatory cytokine responses in BKC, except for IL-6. The endothelial B46 cells exhibited upregulation of IL-1α, IL-1β, and IL-6 3 h after stimulation by LPS. In contrast to the stimulation by LPS, B46 had relatively low pro-inflammatory cytokine responses to DON, except for IL-1α, which was moderately induced at 3 h and increased at 24 h after stimulation. The myofibroblast-like A26 cells exhibited low responses in the induction of pro-inflammatory cytokines to LPS or DON; however, the expression of IL-6 was significantly observed 3 h after DON stimulation. Our results suggest that bovine liver sinusoidal cells have distinctive pro-inflammatory cytokine responses against harmful substances, and these immune responses might determine the consequence of systemic inflammations in the diseased animal.

Uterine-Derived CD11b Cells Significantly Increase Vasculogenesis and Promote Myocardial Healing in Ischemic Cardiomyopathy

Ischemic heart disease is the leading cause of mortality in industrialized countries. Cell transplantation could restore function of the ischemic heart likely through the mechanism of cell-induced angiogenesis. We have previously shown that cells isolated from uteri increase angiogenesis and alleviate cardiac dysfunction when transplanted after MI. However, which uterine cell type contributes to angiogenesis is unknown. Here we report that uterine-derived CD11b cells significantly increase vasculogenesis and promote myocardial healing in ischemic cardiomyopathy. We have established a novel and simple methodology for uterine CD11b cell isolation and enrichment and demonstrate that this technique can be used for purifying and establishing viable CD11b cell cultures in rats. The isolated fresh CD11b cells were transplanted into ischemic rat hearts 5 days after injury. Following transplantation, vasculogenesis significantly increased in ischemic cardiac tissue, which reduced infarct size and restored myocardial function and perfusion compared with controls. Thus, uterine CD11b cells have the potential to promote functional healing when implanted after ischemic cardiomyopathy. Importantly, we have demonstrated a novel means by which CD11b cells can be easily purified and cultured for cell transplantation.

Primary possum macrophage cultures support the growth of a nidovirus associated with wobbly possum disease

The objective of the study was to establish a system for isolation of a recently described, thus far uncultured, marsupial nidovirus associated with a neurological disease of possums, termed wobbly possum disease (WPD). Primary cultures of possum macrophages were established from livers of adult Australian brushtail possums (Trichosurus vulpecula). High viral copy numbers (up to 6.9×10(8)/mL of cell lysate) were detected in infected cell culture lysates from up to the 5th passage of the virus, indicating that the putative WPD virus (WPDV) was replicating in cultured cells. A purified virus stock with a density of 1.09 g/mL was prepared using iodixanol density gradient ultracentrifugation. Virus-like particles approximately 60 nm in diameter were observed using electron microscopy in negatively stained preparations of the purified virus. The one-step growth curve of WPDV in macrophage cultures showed the highest increase in intracellular viral RNA between 6 and 12h post-infection. Maximum levels of cell-associated viral RNA were detected at 24h post-infection, followed by a decline. Levels of extracellular RNA increased starting at 9h post-infection, with maximum levels detected at 48 h post-infection. The establishment of the in vitro system to culture WPDV will facilitate further characterisation of this novel nidovirus.

Establishment of c-myc-immortalized Kupffer cell line from a C57BL/6 mouse strain

We recently demonstrated in several mammalian species, a novel procedure to obtain liver-macrophages (Kupffer cells) in sufficient numbers and purity using a mixed primary culture of hepatocytes. In this study, we applied this method to the C57BL/6 mouse liver and established an immortalized Kupffer cell line from this mouse strain. The hepatocytes from the C57BL/6 adult mouse liver were isolated by a two-step collagenase perfusion method and cultured in T25 culture flasks. Similar to our previous studies, the mouse hepatocytes progressively changed their morphology into a fibroblastic appearance after a few days of culture. After 7-10 days of culture, Kupffer-like cells, which were contaminants in the hepatocyte fraction at the start of the culture, actively proliferated on the mixed fibroblastic cell sheet. At this stage, a retroviral vector containing the human c-myc oncogene and neomycin resistance gene was introduced into the mixed culture. Gentle shaking of the culture flask, followed by the transfer and brief incubation of the culture supernatant, resulted in a quick and selective adhesion of Kupffer cells to a plastic dish surface. After selection with G418 and cloning by limiting dilutions, a clonal cell line (KUP5) was established. KUP5 cells displayed typical macrophage morphology and were stably passaged at 4-5 days intervals for more than 5 months, with a population doubling time of 19 h. KUP5 cells are immunocytochemically positive for mouse macrophage markers, such as Mac-1, F4/80. KUP5 cells exhibited substantial phagocytosis of polystyrene microbeads and the release of inflammatory cytokines upon lipopolysaccharide stimulation. Taken together, KUP5 cells provide a useful means to study the function of Kupffer cells in vitro.

Characterization of the liver-macrophages isolated from a mixed primary culture of neonatal swine hepatocytes

We recently developed a novel procedure to obtain liver-macrophages in sufficient number and purity using a mixed primary culture of rat and bovine hepatocytes. In this study, we aim to apply this method to the neonatal swine liver. Swine parenchymal hepatocytes were isolated by a two-step collagenase perfusion method and cultured in T75 culture flasks. Similar to the rat and bovine cells, the swine hepatocytes retained an epithelial cell morphology for only a few days and progressively changed into fibroblastic cells. After 5–13 days of culture, macrophage-like cells actively proliferated on the mixed fibroblastic cell sheet. Gentle shaking of the culture flask followed by the transfer and brief incubation of the culture supernatant resulted in a quick and selective adhesion of macrophage-like cells to a plastic dish surface. After rinsing dishes with saline, the attached macrophage-like cells were collected at a yield of 10⁶ cells per T75 culture flask at 2–3 day intervals for more than 3 weeks. The isolated cells displayed a typical macrophage morphology and were strongly positive for macrophage markers, such as CD172a, Iba-1 and KT022, but negative for cytokeratin, desmin and a-smooth muscle actin, indicating a highly purified macrophage population. The isolated cells exhibited phagocytosis of polystyrene microbeads and a release of inflammatory cytokines upon lipopolysaccharide stimulation. This shaking and attachment method is applicable to the swine liver and provides a sufficient number of macrophages without any need of complex laboratory equipments.

An efficient method to isolate and culture mouse Kupffer cells

Kupffer cells (KCs) play an essential role in the physiological and pathological functions of the liver. Although the isolation methods of KCs have been well-described, most of them are sophisticated and time-consuming. In addition, these methods are mainly used for isolating the KCs of the human and rat. In this study, a three-step procedure was applied to isolate KCs in sufficient number and purity from mouse liver, including the techniques of enzymatic tissue treatment, gradient centrifugation, and selective adherence. F4/80 immunofluorescence and flow cytometry were used for cell identification. The combination method resulted in a satisfactorily high yield of 5-6×10(6) KCs per liver, over 92.0% positive for F4/80 and 98.5% viable cells. After 24h of culturing, the KCs showed typical macrophage morphologic features such as irregular shape, transparent cytoplasm and kidney-like nucleus. The phagocytic assay showed that the isolated cells exhibited strong phagocytosis activity. The KCs we isolated were functionally intact and exhibited a concentration dependent TNF-α production induced by LPS. The method we described is an effective method to isolate mouse KCs in high purity and yield, which consuming fewer collagenase and time without altering the functional capacity of the KCs.