Phenotypic and functional heterogeneity of porcine blood monocytes and its relation with maturation

Recent advances in antigen targeting to antigen-presenting cells in veterinary medicine

Advances in antigen targeting in veterinary medicine have gained traction over the years as an alternative approach for diseases that remain a challenge for traditional vaccines. In addition to the nature of the immunogen, antigen-targeting success relies heavily on the chosen receptor for its direct influence on the elicited response that will ensue after antigen uptake. Different approaches using antibodies, natural or synthetic ligands, fused proteins, and DNA vaccines have been explored in various veterinary species, with pigs, cattle, sheep, and poultry as the most frequent models. Antigen-presenting cells can be targeted using a generic approach, such as broadly expressed receptors such as MHC-II, CD80/86, CD40, CD83, etc., or focused on specific cell populations such as dendritic cells or macrophages (Langerin, DC-SIGN, XCR1, DC peptides, sialoadhesin, mannose receptors, etc.) with contrasting results. Interestingly, DC peptides show high specificity to DCs, boosting activation, stimulating cellular and humoral responses, and a higher rate of clinical protection. Likewise, MHC-II targeting shows consistent results in enhancing both immune responses; an example of this strategy of targeting is the approved vaccine against the bovine viral diarrhea virus in South America. This significant milestone opens the door to continuing efforts toward antigen-targeting vaccines to benefit animal health. This review discusses the recent advances in antigen targeting to antigen-presenting cells in veterinary medicine, with a special interest in pigs, sheep, cattle, poultry, and dogs.

Characterization of Porcine Monocyte-Derived Macrophages Cultured in Serum-Reduced Medium

The aim of this study was to establish a cell culture system for the generation of porcine monocyte-derived macrophages (MDMs) under reduced-serum conditions. Cultures based on either the Nu-Serum™ Growth Medium Supplement (NUS) or a conventional fetal bovine serum (FBS) were compared, which included the assessment of FBS from two different providers (FBS1 and FBS2). The data obtained confirmed the significant impact of culture conditions on in vitro-generated MDMs. The MDMs cultured under reduced-serum conditions showed increased levels of IL-1β and CD86 mRNA and a proinflammatory cytokine profile, characterized by the increased mRNA expression of IL-23p19, CXCL10, and CCL5. Phagocytic and respiratory burst activities were not adversely affected. Surprisingly, the difference between the two FBSs was much more pronounced than the effect of the reduced-serum supplement. The FBS1 culture conditions gave rise to macrophages with higher surface levels of CD14, CD16, and CD163, a lower CD80 mRNA expression, and an increased induction of IL-10 gene expression. In contrast, none of these trends were observed in macrophage cultures supplemented with FBS2. Instead, the FBS2 culture showed increased levels of IL-1b and CD86 mRNA. In conclusion, reduced-serum culture is a useful tool for in vitro porcine MDM generation, in line with the current research trend of reducing FBS use in biological research.

Cytokine expression by CD163+ monocytes in healthy and Actinobacillus pleuropneumoniae-infected pigs

Distinct monocyte subpopulations have been previously described in healthy pigs and pigs experimentally infected with Actinobacillus pleuropneumoniae (APP). The CD163+ subpopulation of bone marrow (BM), peripheral blood (PB) and lung monocytes was found to play an important role in the inflammatory process. The inflammation is accompanied by elevation of inflammatory cytokines. The aim of the study was to evaluate the contribution of CD163+ monocytes and macrophages to cytokine production during APP-induced lung inflammation. Cytokine production was assessed by flow cytometry (FC) and quantitative PCR (qPCR) in CD163+ monocytes and by qPCR, immunohistochemistry/fluorescence in lungs and tracheobronchial lymph nodes (TBLN). Despite the systemic inflammatory response after APP infection, BM and PB CD163+ monocytes did not express elevated levels of a wide range of cytokines compared to control pigs. In contrast, significant amounts of IL-1β, IL-6, IL-8 and TNF-α were produced in lung lesions and IL-1β in the TBLN. At the protein level, TNF-α was expressed by both CD163+ monocytes and macrophages in lung lesions, whereas IL-1β, IL-6 and IL-8 expression was found only in CD163+ monocytes; no CD163+ macrophages were found to produce these cytokines. Furthermore, the quantification of CD163+ monocytes expressing the two cytokines IL-1β and IL-8 that were most elevated was performed. In lung lesions, 36.5% IL-1β positive CD163+ monocytes but only 18.3% IL-8 positive CD163+ monocytes were found. In conclusion, PB and BM CD163+ monocytes do not appear to contribute to the elevated cytokine levels in plasma. On the other hand, CD163+ monocytes contribute to inflammatory cytokine expression, especially IL-1β at the site of inflammation during the inflammatory process.

Compartment-Specific Differences in the Activation of Monocyte Subpopulations Are Not Affected by Nitric Oxide and Glucocorticoid Treatment in a Model of Resuscitated Porcine Endotoxemic Shock

Inhaled nitric oxide (iNO) remains one of the treatment modalities in shock, and in addition to its vasoactive properties, iNO exerts immunomodulatory effects. We used a porcine model of endotoxemia with shock resuscitation (control) and additional treatment with iNO and a steroid (treatment group). After 20 h, bone marrow (BM), peripheral blood (PB), and bronchoalveolar lavage fluid (BALF) were collected to analyze the immunophenotype and mitochondrial membrane potential (Δφ) in three subsets of monocytes. In both groups, SLA-DR expression decreased twofold on the circulating CD14+CD163+ and CD14−CD163+ monocytes, while it did not change on the CD14+CD163+. Δφ increased only in the CD14−CD163+ subpopulation (0.8 vs. 2.0, p < 0.001). The analysis of compartment-specific alterations showed that nearly 100% of BALF CD14+CD163+ and CD14−CD163+ monocytes expressed SLA-DR, and it was higher compared to PB (32% and 20%, p < 0.0001) and BM (93% and 67%, p < 0.001, respectively) counterparts. BALF CD14+CD163+ had a threefold higher Δφ than PB and BM monocytes, while the Δφ of the other subsets was highest in PB monocytes. We confirmed the compartmentalization of the monocyte response during endotoxemic shock, which highlights the importance of studying tissue-resident cells in addition to their circulating counterparts. The iNO/steroid treatment did not further impair monocyte fitness.

Fruit and Vegetable Supplemented Diet Modulates the Pig Transcriptome and Microbiome after a Two-Week Feeding Intervention

A study was conducted to determine the effects of a diet supplemented with fruits and vegetables (FV) on the host whole blood cell (WBC) transcriptome and the composition and function of the intestinal microbiome. Nine six-week-old pigs were fed a pig grower diet alone or supplemented with lyophilized FV equivalent to half the daily recommended amount prescribed for humans by the Dietary Guideline for Americans (DGA) for two weeks. Host transcriptome changes in the WBC were evaluated by RNA sequencing. Isolated DNA from the fecal microbiome was used for 16S rDNA taxonomic analysis and prediction of metabolomic function. Feeding an FV-supplemented diet to pigs induced differential expression of several genes associated with an increase in B-cell development and differentiation and the regulation of cellular movement, inflammatory response, and cell-to-cell signaling. Linear discriminant analysis effect size (LEfSe) in fecal microbiome samples showed differential increases in genera from Lachnospiraceae and Ruminococcaceae families within the order Clostridiales and Erysipelotrichaceae family with a predicted reduction in rgpE-glucosyltransferase protein associated with lipopolysaccharide biosynthesis in pigs fed the FV-supplemented diet. These results suggest that feeding an FV-supplemented diet for two weeks modulated markers of cellular inflammatory and immune function in the WBC transcriptome and the composition of the intestinal microbiome by increasing the abundance of bacterial taxa that have been associated with improved intestinal health.

Activation of Dendritic Cells in Tonsils Is Associated with CD8 T Cell Responses following Vaccination with Live Attenuated Classical Swine Fever Virus

Classical swine fever (CSF) is a highly contagious disease caused by the classical swine fever virus (CSFV). The live attenuated C-strain vaccine is highly efficacious, initiating protection within several days of delivery. The vaccine strain is detected in the tonsil early after inoculation, yet little is known of the role that tonsillar immune cells might play in initiating protection. Comparing the C-strain vaccine with the pathogenic CSFV Alfort-187 strain, changes in the myeloid cell compartment of the tonsil were observed. CSFV infection led to the emergence of an additional CD163⁺CD14⁺ cell population, which showed the highest levels of Alfort-187 and C-strain infection. There was also an increase in both the frequency and activation status (as shown by increased MHC-II expression) of the tonsillar conventional dendritic cells 1 (cDC1) in pigs inoculated with the C-strain. Notably, the activation of cDC1 cells coincided in time with the induction of a local CSFV-specific IFN-γ⁺ CD8 T cell response in C-strain vaccinated pigs, but not in pigs that received Alfort-187. Moreover, the frequency of CSFV-specific IFN-γ⁺ CD8 T cells was inversely correlated to the viral load in the tonsils of individual animals. Accordingly, we hypothesise that the activation of cDC1 is key in initiating local CSFV-specific CD8 T cell responses which curtail early virus replication and dissemination.

The new emerging ovine pestivirus can infect pigs and confers strong protection against classical swine fever virus

Several emerging pestiviruses have been reported lately, some of which have proved to cause disease. Recently, a new ovine pestivirus (OVPV), isolated from aborted lambs, with high genetic identity to classical swine fever virus (CSFV), has proved to induce reproductive disorders in pregnant ewes. OVPV also generated strong serological and molecular cross-reaction with CSFV. To assess the capacity of OVPV to infect swine, twelve piglets were infected either by intranasal or intramuscular route. Daily clinical evaluation and weekly samplings were performed to determine pathogenicity, viral replication and excretion and induction of immune response. Five weeks later, two pigs from each group were euthanized and tissue samples were collected to study viral replication and distribution. OVPV generated only mild clinical signs in the piglets, including wasting and polyarthritis. The virus was able to replicate, as shown by the RNA levels found in sera and swabs and persisted in tonsil for at least 5 weeks. Viral replication activated the innate and adaptive immunity, evidenced by the induction of interferon-alpha levels early after infection and cross-neutralizing antibodies against CSFV, including humoural response against CSFV E2 and E^rns glycoproteins. Close antigenic relation between OVPV and CSFV genotype 2.3 was detected. To determine the OVPV protection against CSFV, the OVPV-infected pigs were challenged with a highly virulent strain. Strong clinical, virological and immunological protection was generated in the OVPV-infected pigs, in direct contrast with the infection control group. Our findings show, for the first time, the OVPV capacity to infect swine, activate immunity, and the robust protection conferred against CSFV. In addition, their genetic and antigenic similarities, the close relationship between both viruses, suggest their possible coevolution as two branches stemming from a shared origin at the same time in two different hosts.

Heterogeneous populations from in vitro cultures of antigen presenting cells in pigs

Dendritic cells (DCs) are the most potent antigen presenting cells (APCs). Because of the difficulty in obtaining these cells directly from tissues, different sources of DCs are frequently used for in vitro experimentation and many of their biological and functional characteristics were studied using these systems. Until recently, it was assumed that specific culture conditions polarized the differentiation of either DCs or macrophages (Macs); however, it was shown that some DC culture systems in other species generate heterogeneous cell populations that can be identified according to their CD11c and MHC class II (MHC-II) expression. Following this approach, porcine DCs were directly isolated from peripheral blood or differentiated in vitro by culturing bone marrow (BM) progenitor cells or blood monocytes treated with growth factors. Mostly homogeneous monocyte-derived DCs (MoDCs) were obtained with similar phenotype and phagocytic characteristics to that of blood DCs. On the contrary, BM-derived DC (BMDC) cultures generated two distinct heterogeneous populations identified as MHC-II⁺ and MHC-II⁺⁺ cells. BMDCs MHC-II⁺ had similar phenotypic and phagocytic characteristics to those of MoDCs and blood DCs. However, BMDCs MHC-II⁺⁺ population expressed a higher amount of surface markers and transcribed genes associated with Macs-lineage exhibiting a higher phagocytic capacity than all the other cells. Noteworthy, every cell system expressed different genetic signatures. These results will help interpreting and re-interpreting data obtained using in vitro systems.

Recent Advances in Camel Immunology

Camels are domesticated animals that are highly adapted to the extreme desert ecosystem with relatively higher resistance to a wide range of pathogens compared to many other species from the same geographical region. Recently, there has been increased interest in the field of camel immunology. As the progress in the analysis of camel immunoglobulins has previously been covered in many recent reviews, this review intends to summarize published findings related to camel cellular immunology with a focus on the phenotype and functionality of camel leukocyte subpopulations. The review also describes the impact of different physiological (age and pregnancy) and pathological (e.g. infection) conditions on camel immune cells. Despite the progress achieved in the field of camel immunology, there are gaps in our complete understanding of the camel immune system. Questions remain regarding innate recognition mechanisms, the functional characterization of antigen-presenting cells, and the characterization of camel NK and cytotoxic T cells.

An engineered anti-idiotypic antibody-derived killer peptide (KP) early activates swine inflammatory monocytes, CD3+CD16+ natural killer T cells and CD4+CD8α+ double positive CD8β+ cytotoxic T lymphocytes associated with TNF-α and IFN-γ secretion

This study evaluated the early modulation of the phenotype and cytokine secretion in swine immune cells treated with an engineered killer peptide (KP) based on an anti-idiotypic antibody functionally mimicking a yeast killer toxin. The influence of KP on specific immunity was investigated using porcine reproductive and respiratory syndrome virus (PRRSV) and porcine circovirus type 2 (PCV2) as ex vivo antigens. Peripheral blood mononuclear cells (PBMC) from healthy pigs were stimulated with KP and with a scramble peptide for 20 min, 1, 4 and 20 h or kept unstimulated. The cells were analyzed using flow cytometry and ELISA. The same time-periods were used for KP pre-incubation/co-incubation to determine the effect on virus-recalled interferon-gamma (IFN-γ) secreting cell (SC) frequencies and single cell IFN-γ productivity using ELISPOT. KP induced an early dose-dependent shift to pro-inflammatory CD172α⁺CD14^+high monocytes and an increase of CD3⁺CD16⁺ natural killer (NK) T cells. KP triggered CD8α and CD8β expression on classical CD4^-CD8αβ⁺ cytotoxic T lymphocytes (CTL) and double positive (DP) CD4⁺CD8α⁺ Th memory cells (CD4⁺CD8α^+low CD8β^+low). A fraction of DP cells also expressed high levels of CD8α. The two identified DP CD4⁺CD8α^+high CD8β^+low/+high CTL subsets were associated with tumor necrosis factor alpha (TNF-α) and IFN-γ secretion. KP markedly boosted the reactivity and cross-reactivity of PRRSV type-1- and PCV2b-specific IFN-γ SC. The results indicate the efficacy of KP in stimulating Th1-biased immunomodulation and support studies of KP as an immunomodulator or vaccine adjuvant.

The Composition of Circulating Leukocytes Varies With Age and Melanoma Onset in the MeLiM Pig Biomedical Model

Immunological research in pigs benefits from many improvements with a direct impact on the veterinary control of pig husbandry and on biomedical models. We compiled the available knowledge to develop gating strategies to monitor simultaneously all blood immune cell types by multicolor flow cytometry in Melanoblastoma-bearing Libechov Minipigs (MeLiM). The MeLiM pig spontaneously develops cutaneous melanomas that regress few months later. We monitored lymphoid and myeloid cell subsets in 3 to 21 weeks old pigs. Interestingly, neutrophils, type III monocytes (CD163⁺ CD14⁺ MHC II^-) and CD4^- CD8α^- T cells are less abundant in oldest animals in contrast to eosinophils, type II monocytes (CD163^- CD14^low MHC II⁺), B cells, γδ T cells, CD4⁺ CD8α⁺ and CD4^- CD8α⁺ T cells. Melanoma occurrence led to changes in the blood cell composition. Higher proportions of NK cells, CD4⁺ and CD4⁺ CD8α⁺ T cells, and CD21^- B cells among B cells are found in young melanoma-bearing piglets, consistent with the immune-mediated spontaneous regression in the MeLiM model.

Dromedary camel CD14high MHCIIhigh monocytes display inflammatory properties and are reduced in newborn camel calves

Background

In human and different animal species, blood monocytes are classified based on their expression pattern of different monocytic markers into phenotypically and functionally different subsets. In the current study, we used flow cytometry and monoclonal antibodies to CD172a, CD14, CD163 and MHCII to identify monocyte subsets in peripheral blood of dromedary camels.

Results

Based on CD14, CD163 and MHCII expression, camel CD172a + monocytes were divided into three subsets: The major subpopulation of camel monocytes (mo-I) showed high expression of CD14 and CD163, but low expression of MHCII. A second subset of monocytes (mo-II) expressed highly all three markers, CD14, CD163 and MHCII. A third monocyte subset (mo-III) displayed low expression of CD14 and CD163 with high MHCII expression. While the two MHCII^high subsets (mo-II and mo-III) showed higher expression of CD11a in comparison to the MHCII^low subset (mo-I), CD18 and CD11b were highest expressed on the two CD14^high subsets (mo-I and mo-II). Bacterial stimulation of camel leukocytes identified mo-II cells as an antimicrobial monocyte subset with the highest phagocytic and ROS production capacity. The comparison of monocyte counts and phenotype between newborn calves and adult camels revealed significantly reduced numbers of mo-II cells in newborn animals. Monocytes of newborns expressed significantly more CD172a and CD163 molecules but less CD14 and MHCII molecules than monocytes of adult camels.

Conclusions

Camel monocyte subsets, mo-I, mo-II and mo-III are counterparts of bovine classical, intermediate and non-classical monocytes respectively. The distribution of camel monocyte subsets is influenced by age.

Immunophenotyping monocytes, macrophages and granulocytes in the Pteropodid bat Eonycteris spelaea

Bats are asymptomatic reservoir hosts for several highly pathogenic viruses. Understanding this enigmatic relationship between bats and emerging zoonotic viruses requires tools and approaches which enable the comparative study of bat immune cell populations and their functions. We show that bat genomes have a conservation of immune marker genes which delineate phagocyte populations in humans, while lacking key mouse surface markers such as Ly6C and Ly6G. Cross-reactive antibodies against CD44, CD11b, CD14, MHC II, and CD206 were multiplexed to characterize circulating monocytes, granulocytes, bone-marrow derived macrophages (BMDMs) and lung alveolar macrophages (AMs) in the cave nectar bat Eonycteris spelaea. Transcriptional profiling of bat monocytes and BMDMs identified additional markers – including MARCO, CD68, CD163, CD172α, and CD88 – which can be used to further characterize bat myeloid populations. Bat cells often resembled their human counterparts when comparing immune parameters that are divergent between humans and mice, such as the expression patterns of certain immune cell markers. A genome-wide comparison of immune-related genes also revealed a much closer phylogenetic relationship between bats and humans compared to rodents. Taken together, this study provides a set of tools and a comparative framework which will be important for unravelling viral disease tolerance mechanisms in bats.

Towards the quantitative characterisation of piglets' robustness to weaning: a modelling approach

Weaning is a critical transition phase in swine production in which piglets must cope with different stressors that may affect their health. During this period, the prophylactic use of antibiotics is still frequent to limit piglet morbidity, which raises both economic and public health concerns such as the appearance of antimicrobial-resistant microbes. With the interest of developing tools for assisting health and management decisions around weaning, it is key to provide robustness indexes that inform on the animals' capacity to endure the challenges associated with weaning. This work aimed at developing a modelling approach for facilitating the quantification of piglet resilience to weaning. A total of 325 Large White pigs weaned at 28 days of age were monitored and further housed and fed conventionally during the post-weaning period without antibiotic administration. Body weight and diarrhoea scores were recorded before and after weaning, and blood was sampled at weaning and 1 week later for collecting haematological data. A dynamic model was constructed based on the Gompertz-Makeham law to describe live weight trajectories during the first 75 days after weaning, following the rationale that the animal response is partitioned in two time windows (a perturbation and a recovery window). Model calibration was performed for each animal. Our results show that the transition time between the two time windows, as well as the weight trajectories are characteristic for each individual. The model captured the weight dynamics of animals at different degrees of perturbation, with an average coefficient of determination of 0.99, and a concordance correlation coefficient of 0.99. The utility of the model is that it provides biologically meaningful parameters that inform on the amplitude and length of perturbation, and the rate of animal recovery. Our rationale is that the dynamics of weight inform on the capability of the animal to cope with the weaning disturbance. Indeed, there were significant correlations between model parameters and individual diarrhoea scores and haematological traits. Overall, the parameters of our model can be useful for constructing weaning robustness indexes by using exclusively the growth curves. We foresee that this modelling approach will provide a step forward in the quantitative characterisation of robustness.

Guidelines for the use of flow cytometry and cell sorting in immunological studies (second edition)

These guidelines are a consensus work of a considerable number of members of the immunology and flow cytometry community. They provide the theory and key practical aspects of flow cytometry enabling immunologists to avoid the common errors that often undermine immunological data. Notably, there are comprehensive sections of all major immune cell types with helpful Tables detailing phenotypes in murine and human cells. The latest flow cytometry techniques and applications are also described, featuring examples of the data that can be generated and, importantly, how the data can be analysed. Furthermore, there are sections detailing tips, tricks and pitfalls to avoid, all written and peer-reviewed by leading experts in the field, making this an essential research companion.

Bovine Derived in vitro Cultures Generate Heterogeneous Populations of Antigen Presenting Cells

Antigen presenting cells (APC) of the mononuclear phagocytic system include dendritic cells (DCs) and macrophages (Macs) which are essential mediators of innate and adaptive immune responses. Many of the biological functions attributed to these cell subsets have been elucidated using models that utilize in vitro-matured cells derived from common progenitors. However, it has recently been shown that monocyte culture systems generate heterogeneous populations of cells, DCs, and Macs. In light of these findings, we analyzed the most commonly used bovine in vitro-derived APC models and compared them to bona fide DCs. Here, we show that bovine monocyte-derived DCs and Macs can be differentiated on the basis of CD11c and MHC class II (MHCII) expression and that in vitro conditions generate a heterologous group of both DCs and Macs with defined and specific biological activities. In addition, skin-migrating macrophages present in the bovine afferent lymph were identified and phenotyped for the first time. RNA sequencing analyses showed that these monophagocytic cells have distinct transcriptomic profiles similar to those described in other species. These results have important implications for the interpretation of data obtained using in vitro systems.

Interaction of PRRS virus with bone marrow monocyte subsets

PRRSV can replicate for months in lymphoid organs leading to persistent host infections. Porcine bone marrow comprises two major monocyte subsets, one of which expresses CD163 and CD169, two receptors involved in the entry of PRRSV in macrophages. In this study, we investigate the permissiveness of these subsets to PRRSV infection. PRRSV replicates efficiently in BM CD163⁺ monocytes reaching titers similar to those obtained in alveolar macrophages, but with a delayed kinetics. Infection of BM CD163^- monocytes was variable and yielded lower titers. This may be related with the capacity of BM CD163^- monocytes to differentiate into CD163⁺ CD169⁺ cells after culture in presence of M-CSF. Both subsets secreted IL-8 in response to virus but CD163⁺ cells tended to produce higher amounts. The infection of BM monocytes by PRRSV may contribute to persistence of the virus in this compartment and to hematological disorders found in infected animals such as the reduction in the number of peripheral blood monocytes.

Phenotypic and functional characterization of porcine bone marrow monocyte subsets

Monocytes comprise several subsets with distinct phenotypes and functional capacities. Based on CD163 expression, two major monocyte subsets can be discriminated in the porcine bone marrow. The CD163⁺ cells expressed higher levels of SLA-DR, Siglec-1, CD11R1 and CD16 when compared to CD163^- monocytes, whereas no remarkable differences were observed in the expression of other markers analyzed. Gene expression analysis showed differential expression of several chemokine receptor and TLR genes. Both subsets phagocytosed microspheres with similar efficiency. However, CD163^- cells tended to produce higher levels of ROS in response to PMA, whereas CD163⁺ cells were more efficient in endocytosing and processing antigens (DQ-OVA). CD163^- monocytes produced higher levels of TNF-α and IL-10 than CD163⁺ cells when stimulated with LPS or Imiquimod. Both subsets produced similar amounts of IL-8 in response to LPS; however, CD163⁺ cells produced more IL-8 after Imiquimod stimulation. Whether these subsets represent different developmental stages, and how are they related remain to be investigated.

Modulation of type I interferon signaling by African swine fever virus (ASFV) of different virulence L60 and NHV in macrophage host cells

ASFV causes an important disease of domestic swine and wild boar. Currently no vaccine is available, highlighting the necessity to understand ASFV modulation of innate immune responses in natural host cells. With this aim, macrophage cultures enriched in SWC9 and CD163 differentiation markers were infected in parallel with high virulent ASFV/L60 and low virulent ASFV/NHV, the latter lacking MGF 360 and 505/530 genes associated with type I interferon (IFN I) control. IFN I production and signaling were studied after completion of the viral cycles. None of the viruses increased IFN I production in host cells, and accordingly, didn't cause activation of the central mediator of the pathway IRF3. However, upon stimulation by poly:IC treatment during infections, L60 and NHV similarly inhibited IFN I production. This didn't seem to depend on IRF3 modulation since its activation levels were not significantly decreased in L60 infection and were even increased in NHV's, in comparison to stimulated mock infections. The infections didn't evidently activate JAK-STAT pathway mediators STAT1 and STAT2, but did increase expression of interferon stimulated genes (ISGs), to higher levels in NHV than L60 infection. Interestingly, in presence of IFN-α, L60 but not NHV was able to decrease significantly the expression of some of the ISGs tested. Overall, both L60 and NHV were able to inhibit IFN I production in macrophages, through a mechanism not dependent on IRF3 modulation. The high virulent isolate showed however a more effective control of the downstream ISGs expression pathway.

Port d'Entrée for Respiratory Infections - Does the Influenza A Virus Pave the Way for Bacteria?

Bacterial and viral co-infections of the respiratory tract are life-threatening and present a global burden to the global community. Staphylococcus aureus, Streptococcus pneumoniae, and Streptococcus pyogenes are frequent colonizers of the upper respiratory tract. Imbalances through acquisition of seasonal viruses, e.g., Influenza A virus, can lead to bacterial dissemination to the lower respiratory tract, which in turn can result in severe pneumonia. In this review, we summarize the current knowledge about bacterial and viral co-infections of the respiratory tract and focus on potential experimental models suitable for mimicking this disease. Transmission of IAV and pneumonia is mainly modeled by mouse infection. Few studies utilizing ferrets, rats, guinea pigs, rabbits, and non-human primates are also available. The knowledge gained from these studies led to important discoveries and advances in understanding these infectious diseases. Nevertheless, mouse and other infection models have limitations, especially in translation of the discoveries to humans. Here, we suggest the use of human engineered lung tissue, human ex vivo lung tissue, and porcine models to study respiratory co-infections, which might contribute to a greater translation of the results to humans and improve both, animal and human health.

Heterogeneity of Bovine Peripheral Blood Monocytes

Peripheral blood monocytes of several species can be divided into different subpopulations with distinct phenotypic and functional properties. Herein, we aim at reviewing published work regarding the heterogeneity of the recently characterized bovine monocyte subsets. As the heterogeneity of human blood monocytes was widely studied and reviewed, this work focuses on comparing bovine monocyte subsets with their human counterparts regarding their phenotype, adhesion and migration properties, inflammatory and antimicrobial functions, and their ability to interact with neutrophilic granulocytes. In addition, the differentiation of monocyte subsets into functionally polarized macrophages is discussed. Regarding phenotype and distribution in blood, bovine monocyte subsets share similarities with their human counterparts. However, many functional differences exist between monocyte subsets from the two species. In contrast to their pro-inflammatory functions in human, bovine non-classical monocytes show the lowest phagocytosis and reactive oxygen species generation capacity, an absent ability to produce the pro-inflammatory cytokine IL-1β after inflammasome activation, and do not have a role in the early recruitment of neutrophils into inflamed tissues. Classical and intermediate monocytes of both species also differ in their response toward major monocyte-attracting chemokines (CCL2 and CCL5) and neutrophil degranulation products (DGP) in vitro. Such differences between homologous monocyte subsets also extend to the development of monocyte-derived macrophages under the influence of chemokines like CCL5 and neutrophil DGP. Whereas the latter induce the differentiation of M1-polarized macrophages in human, bovine monocyte-derived macrophages develop a mixed M1/M2 macrophage phenotype. Although only a few bovine clinical trials analyzed the correlation between changes in monocyte composition and disease, they suggest that functional differences between human and bovine monocyte subsets are also reflected in their different clinical relevance for distinct diseases. In opposite to the human system, where higher blood cell number of non-classical monocytes was widely correlated with several human infectious and non-infectious diseases, higher counts of bovine intermediate monocytes are suggested as a potential biomarker for inflammatory responses postpartum.

The role of tumor necrosis factor-like weak inducer of apoptosis in atherosclerosis via its two different receptors

At present, it is commonly accepted that atherosclerosis is a chronic inflammatory disease characterized by disorder of the arterial wall. As one of the inflammatory cytokines of the tumor necrosis factor superfamily, tumor necrosis factor-like weak inducer of apoptosis (TWEAK) participates in the formation and progression of atherosclerosis. TWEAK, when binding to its initial receptor, fibroblast growth factor inducible molecule 14 (Fn14), exerts adverse biological functions in atherosclerosis, including dysfunction of endothelial cells, phenotypic change of smooth muscle cells and inflammatory responses of monocytes/macrophages. However, accumulating data supports that, besides Fn14, TWEAK also binds to cluster of differentiation (CD)163, an anti-inflammatory cytokine and a scavenger receptor exclusively expressed by monocytes and macrophages. Furthermore, it has been demonstrated that CD163 is able to internalize TWEAK and likely elicits protective effects in atherosclerosis by terminating inflammation induced by TWEAK. In the present study, the role of TWEAK in atherosclerosis was reviewed, with a predominant focus on CD163 and Fn14 receptors.

Comparative phenotypic and functional analyses of the effects of autologous plasma and recombinant human macrophage-colony stimulating factor (M-CSF) on porcine monocyte to macrophage differentiation

Porcine monocyte-derived macrophages (moMΦ) have been employed as a model cell in numerous studies of the porcine immune system. However, the lack of a standardized method for moMΦ differentiation hampers the comparison of results coming from the use of different laboratory protocols. In this study we compared the use of varying concentrations of autologous plasma (10, 20 and 30% v/v) or recombinant human macrophage-colony stimulating factor (hM-CSF; 50, 100, and 200ng/ml) to differentiate porcine monocytes into macrophages. Changes in cell morphology and surface marker expression were assessed by confocal microscopy and flow cytometry. Macrophage differentiation was evaluated by analysing TNF-α response to LPS stimulation and determining cytokine secretion patterns under both basal conditions and after classical and alternative activation. The effects of the differentiation methods on metabolic activity and susceptibility to infection with the myelotropic African swine fever virus (ASFV) were also evaluated. Monocytes cultured using the different culture conditions tested augmented in dimension and cellular complexity, but increasing porcine plasma concentrations resulted in a dose dependent enhancement in granularity and a marked pleomorphism. As expected, CD163, MHC class II DR and CD203a expression were up-regulated in both hM-CSF (M-CSF-moMΦ) and autologous plasma cultured macrophages (AP-moMΦ), although a lower percentage of CD163⁺ cells were found following differentiation with high percentages of porcine plasma. We observed enhanced number of viable cells using high concentration of hM-CSF compared to porcine plasma, suggesting a proliferative effect. Irrespective of differentiation conditions, monocyte differentiation into macrophages resulted in an increased susceptibility to ASFV and yielded larger amounts of LPS-induced TNF-α. AP-moMΦ showed a higher basal release of IL-1RA compared to those cultured with hM-CSF and displayed a reduced ability to respond to classical activation, suggesting that the use of high percentages of porcine plasma led to the acquisition of a M2-like phenotype. We conclude that all the protocols tested in this study can be considered as suitable to produce porcine moMΦ, although the use of hM-CSF provides high responsiveness to M1 polarization. Since a higher phenotypic and functional inter-animal variability was observed in AP-moMΦ, we propose that the use of low concentration of hM-CSF should be adopted as the method of choice to provide a better reproducibility between experiments.

Influence of Age and Dose of African Swine Fever Virus Infections on Clinical Outcome and Blood Parameters in Pigs

African swine fever (ASF) is a fatal disease for domestic pigs, leading to serious economic losses in countries where ASF is endemic. Despite extensive research, efficient vaccines against ASF are lacking. Since peripheral blood cells are important mediators for vaccines, we study the impact of ASF on blood parameters in pigs with different ages and infected with different doses of ASF virus. Four different groups were studied: (1) 12 weeks of age/low virus dose; (2) 12 weeks of age/high virus dose; (3) 18 weeks of age/low virus dose; and (4) 18 weeks of age/high virus dose. By varying in age and/or ASFV inoculation dose, we monitor blood parameters during different degrees of disease. Thirty percent of the pigs survived the infection with a moderately virulent strain of African swine fever virus (ASFV). Animals that did survive infection were generally older, independent from the inoculation dose used. A firm reduction in many different cell types at 3-5 days postinfection (DPI) was accompanied by an increase in body temperature, followed by clinical signs and mortality from day 6 PI. While blood parameters generally normalized in survivors, γδ T cells and IL-10 levels could be related to mortality. These conclusions should be considered in new approaches for protection against ASF.

Generation of potent porcine monocyte-derived dendritic cells (MoDCs) by modified culture protocol

In vitro derivation of dendritic cells (DCs) is an alternative approach to overcome the low frequency of primary DCs and the difficulty of isolation techniques for studying DC immunobiology. To date, the conventional culture protocol of porcine monocyte-derived DCs (MoDCs) has been widely used. However, this protocol is not practical due to the requirement of a substantial number of blood monocytes, and the process often interferes with DC maturation. To improve in vitro porcine MoDC generation, we modified the previous conventional DC generation protocol, based on the human and mouse primary DC culture system, and compared phenotypic and functional features of MoDCs derived from the modified protocol to the conventional protocol. The modified protocol consumed fewer monocytes but generated higher CD1⁺ cells with DC-like morphology and the ability of maturation. In addition, MoDCs from the modified protocol exhibited increased antigen uptake and IFN-γ production in response to LPS stimulation. Our findings indicate that the modified protocol is expedient and reliable for generating potent MoDCs that substitute for primary DCs. This will be a valuable platform for future research in antigen delivery, vaccines and immunotherapy in pigs, as well as relevant veterinary species.

Phenotypic and functional analysis of monocyte populations in cattle peripheral blood identifies a subset with high endocytic and allogeneic T-cell stimulatory capacity

Circulating monocytes in several mammalian species can be subdivided into functionally distinct subpopulations based on differential expression of surface molecules. We confirm that bovine monocytes express CD172a and MHC class II with two distinct populations of CD14⁺CD16^low/-CD163⁺ and CD14⁻CD16⁺⁺CD163^low- cells, and a more diffuse population of CD14⁺CD16⁺CD163⁺ cells. In contrast, ovine monocytes consisted of only a major CD14⁺CD16⁺ subset and a very low percentage of CD14⁻CD16⁺⁺cells. The bovine subsets expressed similar levels of CD80, CD40 and CD11c molecules and mRNA encoding CD115. However, further mRNA analyses revealed that the CD14⁻CD16⁺⁺ monocytes were CX3CR1^highCCR2^low whereas the major CD14⁺ subset was CX3CR1^lowCCR2^high. The former were positive for CD1b and had lower levels of CD11b and CD86 than the CD14⁺ monocytes. The more diffuse CD14⁺CD16⁺ population generally expressed intermediate levels of these molecules. All three populations responded to stimulation with phenol-extracted lipopolysaccharide (LPS) by producing interleukin (IL)-1β, with the CD16⁺⁺ subset expressing higher levels of IL-12 and lower levels of IL-10. The CD14⁻CD16⁺⁺ cells were more endocytic and induced greater allogeneic T cell responses compared to the other monocyte populations. Taken together the data show both similarities and differences between the classical, intermediate and non-classical definitions of monocytes as described for other mammalian species, with additional potential subpopulations. Further functional analyses of these monocyte populations may help explain inter-animal and inter-species variations to infection, inflammation and vaccination in ruminant livestock.

Molecular and functional characterization of porcine Siglec-3/CD33 and analysis of its expression in blood and tissues

A cDNA clone encoding a 380 a-a type 1 transmembrane protein with homology to human Siglec-3/CD33 was obtained from a swine small intestine library. An analysis of protein sequence identified two immunoglobulin-like domains, a transmembrane region, and a carboxi-terminal tail with two tyrosine-based signalling motifs. Binding assays of Siglec-3 transfected CHO cells to polyacrylamide glycoconjugates showed a preference for α2-6-linked sialic acids. Using mAbs raised against a fragment containing the two Ig-like domains, porcine Siglec-3 was found to be expressed on monocytes and granulocytes, and their bone marrow precursors. It was also detected in lymph node, splenic and alveolar macrophages. MAbs immunoprecipitated, from granulocyte lysates, a protein of 51-60 kDa under both non-reducing and reducing conditions. MAbs were also used to analyse functional activity of Siglec-3 on bone marrow and blood cells. Engagement of Siglec-3 by mAb had no apparent effect on cell proliferation or cytokine production.

Modulation of CD163 expression by metalloprotease ADAM17 regulates porcine reproductive and respiratory syndrome virus entry

As a consequence of their effects on ectodomain shedding, members of the A disintegrin and metalloprotease (ADAM) family have been implicated in the control of various cellular processes. Although ADAM family members are also involved in cancer, inflammation, and other pathologies, it is unclear whether they affect porcine reproductive and respiratory syndrome virus (PRRSV) infection. Here, we demonstrate for the first time that inhibition of ADAM17 enhances PRRSV entry in Marc-145 and porcine alveolar macrophages (PAMs). We also demonstrate that the inhibition of ADAM17 upregulates membrane CD163 expression, a putative PRRSV receptor that is exogenously expressed in BHK-21 and endogenously expressed in Marc-145 and PAMs. Furthermore, overexpression of ADAM17 induced downregulation of CD163 expression and a reduction in PRRSV infection, whereas ablation of ADAM17 expression using specific small interfering RNA resulted in upregulation of CD163 expression with a corresponding increase in PRRSV infection. These ADAM17-mediated effects were confirmed with PRRSV nonpermissive BHK-21 cells transfected with CD163 cDNA. Overall, these findings indicate that ADAM17 downregulates CD163 expression and hinders PRRSV entry. Hence, downregulation of ADAM17 particular substrates may be an additional component of the anti-infection defenses.

IMPORTANCE

ADAM17 is one of the important membrane-associated metalloproteases that mediate various cellular events, as well as inflammation, cancer, and other pathologies. Here, we investigate for the first time the role of the metalloprotease ADAM17 in PRRSV infection. By using inhibitor and genetic modification methods, we demonstrate that ADAM17 negatively regulate PRRSV entry by regulating its substrate(s). More specifically, ADAM 17 mediates the downregulation of the PRRSV cellular receptor CD163. The reduction in CD163 expression represents another component of the anti-infection response initiated by ADAM17.

Correlation of cell surface marker expression with African swine fever virus infection

The expression of surface markers on African swine fever virus (ASFV) infected cells was evaluated to assess their involvement in infection. Previous findings indicated CD163 expression was correlated with ASFV susceptibility. However, in this study the expression of porcine CD163 on cell lines did not increase the infection rate of these cells indicating other factors are likely to be important in determining susceptibility to infection. On adherent porcine bone marrow (pBM) cells the expression of CD45 was strongly correlated with infection. CD163 and CD203a expression correlated at intermediate levels with infection, indicating cells expressing these markers could become infected but were not preferentially infected by the virus. Most of the cells expressing MHCII were infected, indicating that they may be preferentially infected although expression of MHCII was not essential for infection and a large percentage of the infected cells were MHCII negative. CD16 showed a marked decrease in expression following infection and significantly lower levels of infected cells were shown to express CD16. Altogether these results suggest CD163 may be involved in ASFV infection but it may not be essential; the results also highlight the importance of other cell markers which requiring further investigation.

Antigen targeting to APC: from mice to veterinary species

Antigen delivery to receptors expressed on antigen presenting cells (APC) has shown to improve immunogenicity of vaccines in mice. An enhancement of cytotoxic T lymphocyte (CTL), helper T cell or humoral responses was obtained depending on the type of APC and the surface molecule targeted. Although this strategy is being also evaluated in livestock animals with promising results, some discrepancies have been found between species and pathogens. The genetic diversity of livestock animals, the different pattern of expression of some receptors among species, the use of different markers to characterize APC in large animals and sometimes the lack of reagents make difficult to compare results obtained in different species. In this review, we summarize the data available regarding antigen targeting to APC receptors in cattle, sheep and pig and discuss the results found in these animals in the context of what has been obtained in mice.

The Gottingen minipig is a model of the hematopoietic acute radiation syndrome: G-colony stimulating factor stimulates hematopoiesis and enhances survival from lethal total-body γ-irradiation

PURPOSE

We are characterizing the Gottingen minipig as an additional large animal model for advanced drug testing for the acute radiation syndrome (ARS) to enhance the discovery and development of novel radiation countermeasures. Among the advantages provided by this model, the similarities to human hematologic parameters and dynamics of cell loss/recovery after irradiation provide a convenient means to compare the efficacy of drugs known to affect bone marrow cellularity and hematopoiesis.

METHODS AND MATERIALS

Male Gottingen minipigs, 4 to 5 months old and weighing 9 to 11 kg, were used for this study. We tested the standard off-label treatment for ARS, rhG-CSF (Neupogen, 10 μg/kg/day for 17 days), at the estimated LD70/30 total-body γ-irradiation (TBI) radiation dose for the hematopoietic syndrome, starting 24 hours after irradiation.

RESULTS

The results indicated that granulocyte colony stimulating factor (G-CSF) enhanced survival, stimulated recovery from neutropenia, and induced mobilization of hematopoietic progenitor cells. In addition, the administration of G-CSF resulted in maturation of monocytes/macrophages.

CONCLUSIONS

These results support continuing efforts toward validation of the minipig as a large animal model for advanced testing of radiation countermeasures and characterization of the pathophysiology of ARS, and they suggest that the efficacy of G-CSF in improving survival after total body irradiation may involve mechanisms other than increasing the numbers of circulating granulocytes.

Phenotypic and functional heterogeneity of bovine blood monocytes

Murine and human peripheral blood monocytes are heterogeneous in size, granularity, nuclear morphology, phenotype and function. Whether and how bovine blood monocytes follow this pattern was analyzed in this study. Flow cytometrically, classical monocytes (cM) CD14⁺ CD16⁻, intermediate monocytes (intM) CD14⁺ CD16⁺ and nonclassical monocytes (ncM) CD14⁺ CD16⁺ were identified, with cM being the predominant subset (89%). cM showed a significant lower expression of CD172a, intM expressed the highest level of MHC class II molecules, and ncM were low positive for CD163. Compared to cM and intM, ncM showed a significantly reduced phagocytosis capacity, a significantly reduced generation of reactive oxygen species, and reduced mRNA expression of CXCL8, CXCL1 and IL-1β after LPS stimulation. Based on IL-1β secretion after LPS/ATP stimulation, the inflammasome could be activated in cM and intM, but not in ncM. IFNγ increased the expression of CD16 selectively on cM and induced a shift from cM into intM in vitro. In summary, bovine CD172a-positive mononuclear cells define three monocyte subsets with distinct phenotypic and functional differences. Bovine cM and intM share homologies with their human counterparts, whereas bovine ncM are not inflammatory monocytes.

Mononuclear phagocyte system in kidney disease and repair

The mononuclear phagocyte system is comprised of circulating monocytes, tissue macrophages and dendritic cells (DCs) that play key roles in tissue homeostasis, immune surveillance, and immune and non-immune-mediated tissue injury and repair. This review summarizes the various subsets within this system that exhibit significant functional and phenotypic diversity that can adapt to their surrounding microenvironments during inflammation and in response to colony-stimulating factor (CSF)-1. The current understanding of the co-ordination of monocyte infiltration into the homeostatic and diseased kidney through adhesion molecules, chemokines and chemokine receptors, and cytokines are described. Furthermore, the significant confusion and controversy associated with monocyte differentiation into renal macrophages and DCs following infiltration into the kidney, the considerable functional and phenotypic overlap between both tissue populations and their respective roles in immune and non-immune-mediated renal is also discussed. Understanding the factors that control the activation and recruitment of cells from the mononuclear phagocyte system during renal injury may offer an avenue for the development of new cellular and growth factor-based therapies in combination with existing therapies as an alternative treatment option for patients with renal disease.

Comparative analysis of monocyte subsets in the pig

Human and mouse monocyte can be divided into two different subpopulations based on surface marker expression: CD14/16 and Ly6C/CX3CR1, respectively. Monocyte subpopulations in the pig were identified based on reciprocal expression of CD14 and the scavenger receptor CD163. The two populations, CD14(hi)-CD163(low) and CD14(low)-CD163(hi), show approximately equal abundance in the steady-state. Culture of pig PBMCs in CSF1 indicates that the two populations are a maturation series controlled by this growth factor. Gene expression in pig monocyte subpopulations was profiled using the newly developed and annotated pig whole genome snowball microarray. Previous studies have suggested a functional equivalence between human and mouse subsets, but certain genes such as CD36, CLEC4E, or TREM-1 showed human-specific expression. The same genes were expressed selectively in pig monocyte subsets. However, the profiles suggest that the pig CD14(low)-CD163(high) cells are actually equivalent to intermediate human monocytes, and there is no CD14(-) CD16(+) "nonclassical" population. The results are discussed in terms of the relevance of the pig as a model for understanding human monocyte function.

Changes in macrophage phenotype after infection of pigs with Haemophilus parasuis strains with different levels of virulence

Haemophilus parasuis is a colonizer of healthy piglets and the etiological agent of Glässer's disease. Differences in virulence among strains of H. parasuis have been widely observed. In order to explore the host-pathogen interaction, snatch-farrowed colostrum-deprived piglets were intranasally infected with 4 strains of H. parasuis: reference virulent strain Nagasaki, reference nonvirulent strain SW114, field strain IT29205 (from a systemic lesion and virulent in a previous challenge), and field strain F9 (from the nasal cavity of a healthy piglet). At different times after infection, two animals of each group were euthanized and alveolar macrophages were analyzed for the expression of CD163, CD172a, SLA I (swine histocompatibility leukocyte antigen I), SLA II, sialoadhesin (or CD169), and CD14. At 1 day postinfection (dpi), virulent strains induced reduced expression of CD163, SLA II, and CD172a on the surfaces of the macrophages, while nonvirulent strains induced increased expression of CD163, both compared to noninfected controls. At 2 dpi, the pattern switched into a strong expression of CD172a, CD163, and sialoadhesin by the virulent strains, which was followed by a steep increase in interleukin 8 (IL-8) and soluble CD163 in serum at 3 to 4 dpi. The early increase in surface expression of CD163 induced by nonvirulent strains went along with higher levels of IL-8 in serum than those induced by virulent strains in the first 2 days of infection. Alpha interferon (IFN-α) induction was observed only in animals infected with nonvirulent strains. Overall, these results are compatible with a delay in macrophage activation by virulent strains, which may be critical for disease production.

Plasmids expressing porcine interferon gamma up-regulate pro-inflammatory cytokine and co-stimulatory molecule expression which are suppressed by porcine reproductive and respiratory syndrome virus

Porcine reproductive and respiratory syndrome virus (PRRSV) suppresses the pro-inflammatory immune response following infection of myeloid antigen-presenting cells. A reduced pro-inflammatory immune response modulates PRRSV replication, clinical disease, and persistent infection of the virus. Numerous efforts have been made to enhance the pro-inflammatory immune response to PRRSV, but only a few attempts have so far elicited satisfactory results. The present study aims to evaluate in vitro the potential of plasmids expressing porcine interferon gamma (pcDNA-IFNγ) to enhance the expression of pro-inflammatory immune parameters in PRRSV-inoculated monocytes. Naïve blood monocytes from eight PRRSV-seronegative pigs were inoculated with PRRSV and subsequently transfected with pcDNA-IFNγ or pcDNA (empty plasmid vector) and stimulated with lipopolysaccharide (LPS). The mRNA expression levels of IFNγ, interleukin-1 beta (IL-1β), IL-10, IL-12p40, tumor necrosis factor alpha (TNFα), transforming growth factor beta (TGFβ), CD80, and CD86 were evaluated by real-time PCR. The IFNγ, IL-10, and TNFα protein production was determined by ELISA. Compared with PRRSV-inoculated monocyte control, transfection with pcDNA-IFNγ, but not pcDNA, significantly enhanced IFNγ, TNFα, CD80, and CD86 mRNA expression, and IFNγ and TNFα protein production. A slight increase in IL-1β and IL-12p40 mRNA expression was also observed. Neither pcDNA-IFNγ nor pcDNA transfection affected IL-10 and TGFβ expression. Our results thus suggest that pcDNA-IFNγ may be an effective immunostimulator for potentiating the pro-inflammatory immune response to PRRSV.

Pathogenesis of African swine fever in domestic pigs and European wild boar

African swine fever (ASF) is among the most important viral diseases that can affect domestic and feral pigs. Both clinical signs and pathomorphological changes vary considerably depending on strain virulence and host factors. Acute infections with highly virulent virus strains lead to a clinical course that resembles a viral haemorrhagic fever that is characterized by pronounced depletion of lymphoid tissues, apoptosis of lymphocyte subsets, and impairment of haemostasis and immune functions. It is generally accepted that most lesions can be attributed to cytokine-mediated interactions triggered by infected and activated monocytes and macrophages, rather than by virus-induced direct cell damage. Nevertheless, most pathogenetic mechanisms are far from being understood. This review summarizes the current knowledge and discusses implications and research gaps.

CD14++CD16+ monocytes independently predict cardiovascular events: a cohort study of 951 patients referred for elective coronary angiography

OBJECTIVES

The aim of this study was to analyze the yet ill-defined relationship of distinct human monocyte subsets with cardiovascular outcomes in a broad patient population at cardiovascular risk.

BACKGROUND

Monocytes, the most abundant immune cell type found in atherosclerotic plaques, are crucial promoters of atherogenesis. Three distinct human monocyte subsets exist: classical CD14++CD16-, intermediate CD14++CD16+, and nonclassical CD14+CD16++ monocytes. Immunomodulation of distinct monocyte subsets has recently been discussed as a new therapeutic avenue in atherosclerosis.

METHODS

Cardiovascular events in 951 subjects referred for elective coronary angiography were prospectively analyzed. Monocyte subset analysis was performed using flow cytometry, blinded to patients' clinical characteristics, and patients were categorized according to quartiles of total monocyte and monocyte subset counts. The primary endpoint was defined a priori as the first occurrence of cardiovascular death, acute myocardial infarction, or nonhemorrhagic stroke. Endpoint adjudication was done blinded to monocyte subset distribution.

RESULTS

During a mean follow-up period of 2.6 ± 1.0 years, 93 patients experienced the primary endpoint. In univariate Kaplan-Meier analysis, counts of total (p = 0.010), classical CD14++CD16- (p = 0.024), and intermediate CD14++CD16+ (p < 0.001) monocytes predicted the primary endpoint, whereas nonclassical monocytes did not (p = 0.158). After full adjustment for confounders, CD14++CD16+ monocytes remained the only monocyte subset independently related to cardiovascular events (fourth vs. first quartile: hazard ratio: 3.019; 95% confidence interval: 1.315 to 6.928; p = 0.009).

CONCLUSIONS

CD14++CD16+ monocytes independently predicted cardiovascular events in subjects referred for elective coronary angiography. Future studies will be needed to elucidate whether CD14++CD16+ monocytes may become a target cell population for new therapeutic strategies in atherosclerosis.

Effects of interferon-α on the inflammatory response of swine peripheral blood mononuclear cells

Interferon-α (IFN-α) at low concentrations had been previously shown to control the expression of inflammatory cytokine genes in swine pulmonary alveolar macrophages. In the first part of this study, cultured swine peripheral blood mononuclear cells (PBMCs) were supplemented with IFN-α at low/moderate concentrations, and then stimulated with lipopolysaccharide (LPS). The expression of IFN-α, IFN-γ, IL-1β, TNF-α, and IL-6 genes was determined by real-time PCR. IFN-α at low/moderate concentrations did not significantly reduce the expression of any cytokine gene under study, with clear trends though to a concentration-dependent reduction of IL-1β gene expression and to a concentration-dependent increase of IFN-γ gene expression. In vivo, orally administered IFN-α was shown instead to modulate the inflammatory response to early weaning in uncultured PBMCs of specific pathogen-free piglets. As opposed to the in vitro model, the oral IFN-α treatment reduced after weaning the expression of the IFN-γ gene (P < 0.08) and increased that of the IL-1β gene (P < 0.05). There was also a trend to a reduced expression of both IL-6 and TNF-α. The above modulation of cytokine genes expression and the greater daily mean weight gain of treated piglets highlight important regulatory properties of oral IFN-α in the response to the weaning stress.

The mononuclear phagocyte system of the pig as a model for understanding human innate immunity and disease

The biology of cells of the mononuclear phagocyte system has been studied extensively in the mouse. Studies of the pig as an experimental model have commonly been consigned to specialist animal science journals. In this review, we consider some of the many ways in which the innate immune systems of humans differ from those of mice, the ways that pigs may address the shortcomings of mice as models for the study of macrophage differentiation and activation in vitro, and the biology of sepsis and other pathologies in the living animal. With the completion of the genome sequence and the characterization of many key regulators and markers, the pig has emerged as a tractable model of human innate immunity and disease that should address the limited, predictive value of rodents in preclinical studies.

Porcine monocyte subsets differ in the expression of CCR2 and in their responsiveness to CCL2

Monocyte subsets have been shown to differ in the pattern of chemokine receptor expression and their migratory properties, both in human and mouse. Previously we have characterized in the swine several monocyte subpopulations, based on the expression of CD163, Tük4 and SLA-II, which share features with the populations described in human and mouse. Here, we have analysed the expression of different chemokine receptors in the CD163⁻Tük4⁺SLA-II⁻ and CD163⁺Tük4⁻SLA-II⁺ populations of porcine monocytes. CD163⁺Tük4⁻SLA-II⁺ monocytes expressed higher CX₃CR1 but lower CCR2 and CXCR4 mRNA levels than CD163⁻Tük4⁺SLA-II⁻ monocytes. Moreover, porcine CCL2 binding on Tük4⁺SLA-II⁻ but not on Tük4⁻SLA-II⁺ cells was detected by using a CCL2-green fluorescence protein (pCCL2-GFP) fusion protein. Finally, flow cytometric analyses of monocytes recovered after chemotaxis assays show a clear increase in the proportion of Tük4⁺SLA-II⁻ cells in the fraction migrating toward CCL2, consistent with the polarized CCR2 expression in this monocyte population. The pattern of expression of these chemokine receptors reinforces the similarities of these porcine subsets with their human and mouse counterparts.

Porcine mononuclear phagocyte subpopulations in the lung, blood and bone marrow: dynamics during inflammation induced by Actinobacillus pleuropneumoniae

Mononuclear phagocytes (MP) are cells of nonspecific immunity, playing an essential role in defense against bacterial pathogens. Although various MP subpopulations have been described in the pig, relations among these populations in vivo are unknown to date. The present study was aimed at describing porcine MP subpopulations infiltrating inflamed tissue of pigs under in vivo conditions. Actinobacillus pleuropneumoniae (APP) infection was used to induce an inflammatory response. CD172α, CD14, CD163, MHCII and CD203α cell surface molecules were used to identify MP by flow cytometry. Changes in MP subpopulations in the peripheral blood (PB) and bone marrow (BM) compartments along with the analysis of MP appearing in the inflamed lungs were assessed to elucidate the possible origin and maturation stages of the infiltrating MP. The MP population migrating to the inflamed lungs was phenotype CD14⁺ CD163⁺ CD203α^+/− MHCII^+/−. Concomitantly, after APP infection there was an increase in the PB MP CD14⁺ CD163⁺ CD203α⁻ MHC II⁻ population, suggesting that these cells give rise to inflammatory monocytes/macrophages. The CD203α and MHCII molecules appear on these cells after leaving the PB. In healthy animals, the BM MP precursors were represented by CD14⁻ CD163⁻ cells maturing directly into CD14⁺ CD163⁻ that were then released into the PB. After infection, an altered maturation pathway of MP precursors appeared, represented by CD14⁻ CD163⁻ CD203α⁻ MHCII⁻ MP directly switching into CD14⁺ CD163⁺ CD203α⁻ MHCII⁻ MP. In conclusion, two different MP maturation pathways were suggested in pigs. The use of these pathways differs under inflammatory and noninflammatory conditions.