Interferon response in pigs: molecular and biological aspects

Changes in Immune Response during Pig Gestation with a Focus on Cytokines

Pigs have the highest percentage of embryonic death not associated with specific diseases of all livestock species, at 20-45%. During gestation processes, a series of complex alterations can arise, including embryonic migration and elongation, maternal immunological recognition of pregnancy, and embryonic competition for implantation sites and subsequent nutrition requirements and development. Immune cells and cytokines act as mediators between other molecules in highly complex interactions between various cell types. However, other non-immune cells, such as trophoblast cells, are important in immune pregnancy regulation. Numerous studies have shed light on the crucial roles of several cytokines that regulate the inflammatory processes that characterize the interface between the fetus and the mother throughout normal porcine gestation, but most of these reports are limited to the implantational and peri-implantational periods. Increase in some proinflammatory cytokines have been found in other gestational periods, such as placental remodeling. Porcine immune changes during delivery have not been studied as deeply as in other species. This review details some of the immune system cells actively involved in the fetomaternal interface during porcine gestation, as well as the principal cells, cytokines, and molecules, such as antibodies, that play crucial roles in sow pregnancy, both in early and mid-to-late gestation.

IFN-γ and IL-10: seric and placental profile during pig gestation Seric and placental cytokines in pig gestation

Concentration of interferon-gamma and interleukin-10 in maternal serum and in maternal and fetal porcine placental extracts from different gestation periods was determined. Crossbred pigs' placental samples of 17, 30, 60, 70, and 114 days gestation and non-pregnant uteri were used. Interferon-gamma concentration was increased at the placental interface at 17 days, in maternal and fetal placenta, and decreased significantly in the remaining gestation periods. Interferon-gamma showed a peak in serum at 60 days. Regarding interleukin-10, placental tissue concentrations were unaltered, there were no significant differences with non-gestating uteri samples. In serum interleukin-10 increased at 17, 60, and 114 days gestation. At 17 days there are uterus structural and molecular changes that allow the embryos implantation and placenta development. The presence of interferon-gamma found at this moment in the interface would favor that placental growth. Moreover, its significant increase in serum at 60 days, would generate a proinflammatory cytokine pattern that facility the placental remodeling characteristic of this moment of porcine gestation. On the other hand, a significant interleukin-10 increase in serum at 17, 60 and 114 days could indicate its immunoregulatory role at a systemic level during pig gestation.

Mesenteric lymph node cells from neonates present a prominent IL-12 response to CpG oligodeoxynucleotide via an IL-15 feedback loop of amplification

At birth, the immune system is still in development making neonates more susceptible to infections. The recognition of microbial ligands is a key step in the initiation of immune responses. It can be mimicked to stimulate the immune system by the use of synthetic ligands recognising pattern recognition receptors. In human and mouse, it has been found that neonatal cytokine responses to toll-like receptor (TLR) ligands differ in many ways from those of adults but the relevant studies have been limited to cord blood and spleen cells. In this study, we compared the responses in neonate and adult sheep to CpG oligodeoxynucleotides (ODN), a TLR9 ligand, in both a mucosal and a systemic organ. We observed that in response to CpG-ODN more IL-12 was produced by neonatal than adult sheep cells from mesenteric lymph nodes (MLN) and spleen. This higher IL-12 response was limited to the first 20 days after birth for MLN cells but persisted for a longer period for spleen cells. The major IL-12-producing cells were identified as CD14⁺CD11b⁺. These cells were poor producers of IL-12 in response to direct stimulation with CpG-ODN and required the cooperation of other MLN cells. The difference in response to CpG-ODN between neonates and adults can be attributed to both a higher proportion of CD14⁺CD11b⁺ cells in neonate lambs and their higher capacity to produce IL-15. The IL-15 increases IL-12 production by an amplifying feedback loop involving CD40.

De l’utilité des animaux domestiques pour la recherche en immunologie

Les recherches en immunologie des animaux domestiques fournissent des données complémentaires à celles menées chez la souris, du fait des « opportunités » qu’offrent ces espèces. Certaines d’entre elles font l’objet de cette communication: approche chirurgicale du fonctionnement in vivo des organes lymphoïdes, interventions in utero pour l’étude de l’ontogénèse du système immunitaire, pertinence de l’étude physiopathologique des infections sur espèces cibles.

Antiviral activity of bovine uterus and placenta induced by Newcastle disease virus

The antiviral activity profile of the uterus and fetal membranes from bovine placenta, induced by the Newcastle disease virus (NDV) throughout gestation, was investigated. Explants of the endometrium and caruncles were collected from the uterus, and amniochorion, allantochorion and cotyledons, from fetal placenta. Tissue cultures were induced with ~6.0 hemagglutinating units (HU) of NDV. Supernatants were concentrated 20 fold, filtered in 100kDa cut-off membranes and antiviral activity was titrated in MDBK x VSV system. Tissues of the uterus did not exhibit antiviral activity, while allantochorion and amniochorion produced antiviral factors throughout gestation. Antiviral factors were not related with IFN-alpha, gamma, tau or TNF-alpha. The antiviral activity pattern observed showed to be related with the development of fetal membranes and increased at the end of pregnancy. Such data suggest that IFN genes inducible by virus are present in fetal membranes of the cow placenta and their expression is dependent on the age of gestation.

Characterization of the porcine alpha interferon multigene family

The availability of data on the pig genome sequence prompted us to characterize the porcine IFN-alpha (PoIFN-alpha) multigene family. Fourteen functional PoIFN-alpha genes and two PoIFN-alpha pseudogenes were detected in the porcine genome. Multiple sequence alignment revealed a C-terminal deletion of eight residues in six subtypes. A phylogenetic tree of the porcine IFN-alpha gene family defined the evolutionary relationship of the various subtypes. In addition, analysis of the evolutionary rate and the effect of positive selection suggested that the C-terminal deletion is a strategy for preservation in the genome. Eight PoIFN-alpha subtypes were isolated from the porcine liver genome and expressed in BHK-21 cells line. We detected the level of transcription by real-time quantitative RT-PCR analysis. The antiviral activities of the products were determined by WISH cells/Vesicular Stomatitis Virus (VSV) and PK 15 cells/Pseudorabies Virus (PRV) respectively. We found the antiviral activities of intact PoIFN-alpha genes are approximately 2-50 times higher than those of the subtypes with C-terminal deletions in WISH cells and 15-55 times higher in PK 15 cells. There was no obvious difference between the subtypes with and without C-terminal deletion on acid susceptibility.

Cytokines as markers for infections and their effect on growth performance and well-being in the pig

Exposure to micro-organisms commonly elicit the production of cytokines. These soluble factors enhance several innate immune functions that aim to limit the spread of infection. Further, many of the pro-inflammatory cytokines regulate the ensuing specific immune response. In addition to their effects on cells of the immune system, cytokines also are important regulators in the so called immune-neuroendocrine network. The microbial structures that are necessary for induction of cytokine production are not conclusively determined but in general, bacteria preferentially induce the production of IL-1, TNF-alpha, IL-6, and IL-8, whereas virus induce the production of Type 1 interferons (IFN-alpha/beta). The onset of production of these cytokines is rapid, and several of them may reach systemic levels during a short period after infection. Thus, cytokines can serve as markers for ongoing infections and be used for discrimination between infections of bacterial or viral origin. Results from experimental and field studies show that serum IFN-alpha and IL-6 seem to be useful markers for ongoing (subclinical) viral and bacterial infections, respectively, in the pig. Consequently, demonstration of these cytokines can be valuable tools in heard health monitoring programs.

Clinical effects of the recombinant feline interferon-omega on experimental parvovirus infection in beagle dogs

The clinical effects of recombinant feline interferon-omega (rFeIFN-omega), produced in silkworm by recombinant baculovirus, were examined in 3-4 month-old beagle dogs given an experimental canine parvovirus type-2 (CPV-2) infection. Clinical symptoms, such as pyrexia, vomiting, anorexia and diarrhea, were observed on day 4 after oral inoculation of 10(7) TCID50 of CPV-2 (cc 238 strain) in almost all the inoculated dogs. From day 4, rFeIFN-omega (1 mega units/kg/day) or physiological saline was administered intravenously to infected dogs for 3 consecutive days. Seven out of 17 dogs treated with physiological saline showed hemorrhagic diarrhea and continuously expressed severe clinical enteritis; one dog died with a large amount of hemorrhagic rice-water stool on day 6 after viral exposure. In contrast, 4 out of 12 dogs treated with rFeIFN-omega showed severe clinical enteritis associated with intermittent diarrhea. Scoring of fecal condition revealed that treatment with rFeIFN-omega significantly shifted the enteritis from a severe to mild form. Furthermore, rFeIFN-omega administered in the morning decreased the number of dogs expressing clinical enteritis in the evening suggesting a rapid effect. Vomiting and anorexia were also improved by treatment with rFeIFN-omega. These results suggest that rFeIFN-omega can reduce severe enteritis caused by CPV-2 infection in dogs.

Quantitative detection of porcine interferon-gamma in response to mitogen, superantigen and recall viral antigen

Five monoclonal antibodies (mAbs) specific for porcine interferon-gamma (PoIFN-gamma) were isolated and utilized to develop a PoIFN-gamma sandwich ELISA. Specific reactivity of each mAb with E. coli derived recombinant PoIFN-gamma, but not with rPoIL-2 or rPolL-10, was confirmed in an indirect ELISA and in Western blots. Competitive ELISAs showed that mAbs P2A4 and P2C11 bound an epitope which was not recognized by mAbs P2G10, P1B7 or P2F6. The latter three mAbs were able to neutralize the ability of natural and recombinant PoIFN-gamma to induce the de novo expression of class II MHC antigens on porcine endothelial cells. To simplify the detection of biologically active porcine IFN-gamma, a sandwich ELISA was developed using the mAb P2G10 as a capture antibody and mAb P2C11 as the detecting reagent. The sensitivity of the assay for PolFN-gamma ranged from 1 to 50 ng/ml. Peripheral blood mononuclear cells (PBMC) from all pigs tested produced IFN-gamma when stimulated with either mitogen (PHA) or superantigen (SEB). In contrast, only PBMC obtained from pigs which had previously been vaccinated against PrV produced IFN-gamma in response to stimulation with this virus. Interestingly, cultures with the highest lymphoproliferative response did not necessarily have the highest level of IFN-gamma production.Furthermore, for recall viral antigen, the lymphoproliferative response decreased with time after immunization, whereas the IFN-gamma response increased. Thus, measurement of IFN-gamma production appears to be a good indicator of anti-viral immunological memory.

Tissue chambers--a useful model for in vivo studies of cytokine production in the pig

An in vivo tissue chamber model was developed to enable studies of local cytokine production and cellular events during inflammatory and immune reactions in the pig. Tissue chambers made of sialistic rubber tubing were surgically implanted in the subcutaneous tissue- and samples of tissue chamber fluid (TCF) and inflammatory cells were collected by aspiration with a syringe. To evaluate the model for local cytokine production, two cytokine inducers, polyribinosinic-polyribocytidylic acid (poly I:C) and fixed Aujeszky's disease virus infected PK15 cells (ADV-PK15), were injected into the tissue chambers and samples of TCF were collected 0, 4, 8, 12, 24 and 48 h post injection. Poly I:C injections induced local production of interferon-alpha (IFN-alpha) as well as tumor necrosis factor (TNF) in the TCF but kinetic differences in the production of the cytokines were noted. Poly I:C also induced an increase in cell numbers in the TCF, mainly due to increased neutrophil numbers. Injections of ADV-PK15 induced local IFN-alpha production in the TCF as long as the pigs were serologically negative to ADV. Immunofluorescence and in situ hybridization techniques could be applied for characterization of TCF cells. Moreover, cells recovered from the tissue chambers were viable and could be used in functional in vitro tests. Taken together, this tissue chamber model could prove very useful in in vivo studies of inflammatory/immune responses and cytokine production in the pig.

Immunity to transmissible gastroenteritis virus and porcine respiratory coronavirus infections in swine

Despite the pioneering efforts to identify correlates of passive immunity to transmissible gastroenteritis virus (TGEV), effective vaccines for the control of TGE in suckling pigs have remained elusive. The initial concept of an enteromammary immunologic axis in monogastrics originated from studies of lactogenic immunity to TGEV in swine. These studies revealed that infection of pregnant swine with virulent TGEV stimulated high titers of SIgA antibodies in milk which correlated with protection of suckling pigs against TGE; parenteral or oral inoculation with live attenuated or killed TGEV vaccines induced mainly IgG antibodies in milk which generally provided poor protection to suckling pigs. The recent appearance of PRCV infections in swine and continuing studies of TGEV infections, present a unique model for further studies of mucosal immunity. Research using these viruses has increased our understanding of the various components of the common mucosal immune system and their interactions. Although the most important consideration in designing an effective vaccine for TGEV is the stimulation of GALT through intestinal virus replication, studies addressing the contribution of BALT to immunity to TGEV and PRCV may provide insights for alternative vaccine approaches. The mechanism by which exposure to PRCV elicits a variable-degree of immunity to TGEV challenge is unknown. Virus replication in the gut or respiratory tract is a major factor affecting the magnitude of the immune response at the respective site and may be necessary for the recruitment of specific immune cells from other mucosal inductive sites, i.e., GALT to BALT and BALT to GALT migration.(ABSTRACT TRUNCATED AT 250 WORDS)