Steady state pig dendritic cells migrating in skin draining pseudo-afferent lymph are semi-mature

Immunosafety evaluation in Juvenile Göttingen Minipigs

Although an extrapolation from the clinical experience in adults can often be considered to support the pediatric use for most pharmaceutical compounds, differences in safety profiles between adult and pediatric patients can be observed. The developing immune system may be affected due to exaggerated pharmacological or non-expected effects of a new drug. Toxicology studies in juvenile animals could therefore be required to better evaluate the safety profile of any new pharmaceutical compound targeting the pediatric population. The Göttingen minipig is now considered a useful non-rodent species for non-clinical safety testing of human pharmaceuticals. However, knowledge on the developing immune system in juvenile minipigs is still limited. The objective of the work reported here was to evaluate across-age proportions of main immune cells circulating in blood or residing in lymphoid organs (thymus, spleen, lymph nodes) in Göttingen Minipigs. In parallel, the main immune cell populations from healthy and immunocompromised piglets were compared following treatment with cyclosporin A (CsA) at 10 mg/kg/day for 4 wk until weaning. The study also assessed functionality of immune responses using an in-vivo model after "Keyhole limpet hemocyanin" (KLH) immunization and an ex-vivo lymph proliferation assay after stimulation with Concanavalin A. The results demonstrated variations across age in circulating immune cell populations including CD21⁺ B-cells, αβ-T- and γδ-T-cells, NK cells, and monocytes. CsA-induced changes in immune functions were only partially recovered by 5 mo after the end of treatment, whereas the immune cell populations affected by the treatment returned to normal levels in animals of the same age. Taken together, the study here shows that in this model, the immune function endpoints were more sensitive than the immunophenotyping endpoints.

Skin immune cell characterization in juvenile and adult Göttingen Minipigs

The skin hosts a sophisticated immune system involving responses from both innate and adaptive immune cell populations. Swine skin is close to human skin by its structure, composition and function. In addition, the minipig is considered the model of choice in toxicology studies for drugs applied by the dermal route and developed for both the adult and paediatric indications. However, knowledge on the skin immune system in minipigs, particularly in Göttingen Minipigs, is still limited. The objective of our work was first to characterize the main skin immune populations (Langerhans cells, dermal dendritic cells, macrophages and T lymphocytes) in Göttingen Minipigs. In parallel, we compared the skin immune populations from healthy and immunocompromised piglets following oral treatment with cyclosporin A (CsA) at 10 mg/kg/day. We also explored other pathological conditions using a contact dermatitis model in minipigs challenged with a sensitizer, 2,4-dinitrochlorobenzene (DNCB). Langerhans cells and dermal MHCII^lowCD163⁺ cells were increased one month after oral treatment with CsA at 10 mg/kg/day. The contact dermatitis model in Göttingen Minipigs challenged by DNCB suggested migration of Langerhans cells and dermal dendritic cells as well as T cell recruitment into the skin. These data bring new information in skin immunotoxicology in Göttingen Minipigs and could contribute to a better understanding of the effects of new therapeutic drugs on the developing immune system.

Innate immune response profiles in pigs injected with vaccine adjuvants polydi(sodium carboxylatoethylphenoxy)phosphazene (PCEP) and Emulsigen

Vaccines are formulated with adjuvants to enhance or direct antigen-specific immune responses against pathogens. However, the mechanisms of action (MOA) of adjuvants are not well understood and are under-investigated in large animal species. We have previously reported that injection of mice induced innate immune responses as indicated by increased cell recruitment and cytokine production at the site of injection with polyphosphazene (PCEP) adjuvant. In the present study, we evaluated whether PCEP induced similar innate immune responses in pigs. Piglets were injected with either PCEP or Emulsigen intradermally (I.D.) and the local cellular infiltration and cytokine production were evaluated at the site of injection and the draining lymph nodes. PCEP induced infiltration of macrophages, T and B cells, leucocytes and necrotic debris at the site of injection as well as PCEP-induced leucocyte infiltration in the draining lymph nodes. Emulsigen induced diffuse infiltration of leucocytes, macrophages, and lymphocytes at the site of injection as well as at the draining lymph nodes. PCEP induced significant production of interleukin IL-1β, and IL-13 at the site of injection and IL-1β, and IL-6 at the draining lymph nodes. Emulsigen promoted the production of IL-1β, IL-6, and IL-12 at the site of injection but not in the draining lymph nodes. No cytokines were detected in blood after injection of either adjuvant. Together, our data indicate that in pigs, the adjuvants PCEP and Emulsigen stimulate early innate immune responses at the injection site by creating an immunocompetent environment that may contribute to increased immunogenicity of the co-administered antigens.

Subset-Specific Expression of Toll-Like Receptors by Bovine Afferent Lymph Dendritic Cells

Within the ruminant system, several possibilities exist to generate dendritic cells migrating out from the tissue into the regional draining lymph nodes as afferent lymph dendritic cells (ALDCs). Here, we analyzed toll-like receptor (TLR) 1-10 mRNA expression by using quantitative real-time PCR in highly purified subsets of bovine ALDC. As TLR expression may be influenced by pathogens or vaccines and their adjuvant, it is necessary to understand what TLRs are expressed in a steady-state system to elucidate specific differences and to potentially optimize targeted vaccines. In this study, we have assessed the TLR expression profiles of the four main bovine ALDC subsets [cDC1 and cDC2 (subsets 2-4)]. We demonstrate differences in TLR expression between the four subsets that may reflect the ability of these cells to respond to different pathogens or to respond to adjuvants.

Immunology of bovine respiratory syncytial virus in calves

Bovine respiratory syncytial virus (BRSV) is an important cause of respiratory disease in young calves. The virus is genetically and antigenically closely related to human (H)RSV, which is a major cause of respiratory disease in young infants. As a natural pathogen of calves, BRSV infection recapitulates the pathogenesis of respiratory disease in man more faithfully than semi-permissive, animal models of HRSV infection. With the increasing availability of immunological reagents, the calf can be used to dissect the pathogenesis of and mechanisms of immunity to RSV infection, to analyse the ways in which the virus proteins interact with components of the innate response, and to evaluate RSV vaccine strategies. Passively transferred, neutralising bovine monoclonal antibodies, which recognise the same epitopes in the HRSV and BRSV fusion (F) protein, can protect calves against BRSV infection, and depletion of different T cells subsets in calves has highlighted the importance of CD8(+) T cells in viral clearance. Calves can be used to model maternal-antibody mediated suppression of RSV vaccine efficacy, and to increase understanding of the mechanisms responsible for RSV vaccine-enhanced respiratory disease.

The porcine innate immune system: an update

Over the last few years, we have seen an increasing interest and demand for pigs in biomedical research. Domestic pigs (Sus scrofa domesticus) are closely related to humans in terms of their anatomy, genetics, and physiology, and often are the model of choice for the assessment of novel vaccines and therapeutics in a preclinical stage. However, the pig as a model has much more to offer, and can serve as a model for many biomedical applications including aging research, medical imaging, and pharmaceutical studies to name a few. In this review, we will provide an overview of the innate immune system in pigs, describe its anatomical and physiological key features, and discuss the key players involved. In particular, we compare the porcine innate immune system to that of humans, and emphasize on the importance of the pig as model for human disease.

Incorporation of CpG into a liposomal vaccine formulation increases the maturation of antigen-loaded dendritic cells and monocytes to improve local and systemic immunity

Liposomal vaccine formulations incorporating stimulants that target innate immune receptors have been shown to significantly increase vaccine immunity. Following vaccination, innate cell populations respond to immune stimuli, phagocytose and process Ag, and migrate from the injection site, via the afferent lymphatic vessels, into the local lymph node. In this study, the signals received in the periphery promote and sculpt the adaptive immune response. Effector lymphocytes then leave the lymph node via the efferent lymphatic vessel to perform their systemic function. We have directly cannulated the ovine lymphatic vessels to detail the in vivo innate and adaptive immune responses occurring in the local draining lymphatic network following vaccination with a liposome-based delivery system incorporating CpG. We show that CpG induces the rapid recruitment of neutrophils, enhances dendritic cell-associated Ag transport, and influences the maturation of innate cells entering the afferent lymph. This translated into an extended period of lymph node shutdown, the induction of IFN-γ-positive T cells, and enhanced production of Ag-specific Abs. Taken together, the results of this study quantify the real-time in vivo kinetics of the immune response in a large animal model after vaccination of a dose comparable to that administered to humans. This study details enhancement of numerous immune mechanisms that provide an explanation for the immunogenic function of CpG when employed as an adjuvant within vaccines.

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.

Early inflammatory response to the saponin adjuvant Matrix-M in the pig

The early inflammatory response to Matrix-M was evaluated in pigs. Adverse reactions measured as body temperature, appetite, activity level and reaction at the site of injection were not observed after s.c. injection with three doses of the adjuvant (75, 100 or 150μg) into one week old piglets. Analyses of the immediate cytokine response of PBMC after in vitro exposure to Matrix-M (AbISCO-100(®)) revealed only a low expression of mRNA for tumour necrosis factor-α (p<0.05) after 6h incubation. Histological examination revealed an infiltration of leukocytes, haemorrhage and necrosis in muscle 24h after i.m. injection of 150μg Matrix-M in pigs aged eleven weeks. At this time, different grades of reactive lymphoid hyperplasia were recorded in the draining lymph node that was enlarged in three of these six pigs injected with Matrix-M. The global transcriptional response at the site of injection and in the draining lymph node was analyzed using Affymetrix GeneChip Porcine Genome Array. A significant enrichment of gene signatures for the cell types described as "myeloid cells" and "plasmacytoid dendritic cells" was observed at the site of injection in Matrix-M injected pigs compared with pigs injected with saline. A number of genes encoding cytokines/chemokines or their receptors were upregulated at the injection site as well as in the draining lymph node. In the draining lymph node, a majority of the upregulated genes were interferon-regulated genes (IRGs). The expression of IFN-β, but not IFN-α, was increased in the draining lymph nodes of a majority of the pigs exposed to Matrix-M. These IFN-β expressing pigs also expressed increased levels of osteopontin (OPN) or stimulator of interferon genes (STING), two factors known to facilitate the expression of type I IFNs in response to viral infection. Thus, Matrix-M does not appear to induce any harmful inflammatory response in piglets whilst contributing to the innate immunity by activating the type I IFN system, possibly through several alternative signalling pathways.

Therapeutic potential of semi-mature dendritic cells for tolerance induction

Dendritic cells (DCs) are major players in the control of adaptive tolerance and immunity. Therefore, their specific generation and adoptive transfer into patients or their in vivo targeting is attractive for clinical applications. While injections of mature immunogenic DCs are tested in clinical trials, tolerogenic DCs still are awaiting this step. Besides the tolerogenic potential of immature DCs, also semi-mature DCs can show tolerogenic activity but both types also bear unfavorable features. Optimal tolerogenic DCs, their molecular tool bar, and their use for specific diseases still have to be defined. Here, the usefulness of in vitro generated and adoptively transferred semi-mature DCs for tolerance induction is outlined. The in vivo targeting of semi-mature DCs as represented by steady state migratory DCs are discussed for treatment of autoimmune diseases and allergies. First clinical trials with transcutaneous allergen application may point to their therapeutic use in the future.