Impaired T-cell responses in domestic pigs and wild boar upon infection with a highly virulent African swine fever virus strain

Single-cell profiling of African swine fever virus disease in the pig spleen reveals viral and host dynamics

African swine fever, one of the major viral diseases of swine, poses an imminent threat to the global pig industry. The high-efficient replication of the causative agent African swine fever virus (ASFV) in various organs in pigs greatly contributes to the disease. However, how ASFV manipulates the cell population to drive high-efficient replication of the virus in vivo remains unclear. Here, we found that the spleen reveals the most severe pathological manifestation with the highest viral loads among various organs in pigs during ASFV infection. By using single-cell-RNA-sequencing technology and multiple methods, we determined that macrophages and monocytes are the major cell types infected by ASFV in the spleen, showing high viral-load heterogeneity. A rare subpopulation of immature monocytes represents the major population infected at late infection stage. ASFV causes massive death of macrophages, but shifts its infection into these monocytes which significantly arise after the infection. The apoptosis, interferon response, and antigen-presentation capacity are inhibited in these monocytes which benefits prolonged infection of ASFV in vivo. Until now, the role of immature monocytes as an important target by ASFV has been overlooked due to that they do not express classical monocyte marker CD14. The present study indicates that the shift of viral infection from macrophages to the immature monocytes is critical for maintaining prolonged ASFV infection in vivo. This study sheds light on ASFV tropism, replication, and infection dynamics, and elicited immune response, which may instruct future research on antiviral strategies.

Immune cell early activation, apoptotic kinetic, and T-cell functional impairment in domestic pigs after ASFV CADC_HN09 strain infection

African swine fever (ASF) caused by the African swine fever virus (ASFV) is a fatal and highly contagious disease of domestic pigs characterized by rapid disease progression and death within 2 weeks. How the immune cells respond to acute ASFV infection and contribute to the immunopathogenesis of ASFV has not been completely understood. In this study, we examined the activation, apoptosis, and functional changes of distinct immune cells in domestic pigs following acute infection with the ASFV CADC_HN09 strain using multicolor flow cytometry. We found that ASFV infection induced broad apoptosis of DCs, monocytes, neutrophils, and lymphocytes in the peripheral blood of pigs over time. The expression of MHC class II molecule (SLA-DR/DQ) on monocytes and conventional DCs as well as CD21 expression on B cells were downregulated after ASFV infection, implying a potential impairment of antigen presentation and humoral response. Further examination of CD69 and ex vivo expression of IFN-γ on immune cells showed that T cells were transiently activated and expressed IFN-γ as early as 5 days post-infection. However, the capability of T cells to produce cytokines was significantly impaired in the infected pigs when stimulated with mitogen. These results suggest that the adaptive cellular immunity to ASFV might be initiated but later overridden by ASFV-induced immunosuppression. Our study clarified the cell types that were affected by ASFV infection and contributed to lymphopenia, improving our understanding of the immunopathogenesis of ASFV.

Innate immune escape and adaptive immune evasion of African swine fever virus: A review

African swine fever virus (ASFV) causes hemorrhagic fever in domestic and wild pigs. The continued spread of the virus in Africa, Europe and Asia threatens the global pig industry. The lack of an effective vaccine limits disease control. ASFV has evolved a variety of encoded immune escape proteins and can evade host adaptive immunity, inducing cellular inflammation, autophagy, or apoptosis in host cells. Frequent persistent infections hinder the development of a viral vaccine and impose technical barriers. Currently, knowledge of the virulence-related genes, main pathogenic genes and immunoregulatory mechanism of ASFV is not comprehensive. We explain that ASFV invades the host to regulate its inflammatory response, interferon production, antigen presentation and cellular immunity. Furthermore, we propose potential ideas for ASFV vaccine target design, such as knocking out high-virulence genes in ASFV and performing data mining to identify the main genes that induce antiviral responses. To support a rational strategy for vaccine development, a better understanding of how ASFV interacts with the host and regulates the host's response to infection is needed. We review the current knowledge about ASFV targeting of host innate and adaptive immunity and the mechanisms by which the affected immune pathways are suppressed.

Bridging the Gap: Can COVID-19 Research Help Combat African Swine Fever?

African swine fever (ASF) is a highly contagious and economically devastating disease affecting domestic pigs and wild boar, caused by African swine fever virus (ASFV). Despite being harmless to humans, ASF poses significant challenges to the swine industry, due to sudden losses and trade restrictions. The ongoing COVID-19 pandemic has spurred an unparalleled global research effort, yielding remarkable advancements across scientific disciplines. In this review, we explore the potential technological spillover from COVID-19 research into ASF. Specifically, we assess the applicability of the diagnostic tools, vaccine development strategies, and biosecurity measures developed for COVID-19 for combating ASF. Additionally, we discuss the lessons learned from the pandemic in terms of surveillance systems and their implications for managing ASF. By bridging the gap between COVID-19 and ASF research, we highlight the potential for interdisciplinary collaboration and technological spillovers in the battle against ASF.

Evaluation of Haematological and Immunological Parameters of the ASFV Lv17/WB/Rie1 Strain and Its Derived Mutant Lv17/WB/Rie1/d110-11L against ASFV Challenge Infection in Domestic Pigs

African swine fever virus (ASFV) is the etiological agent of a haemorrhagic disease that threatens the global pig industry. There is an urgency to develop a safe and efficient vaccine, but the knowledge of the immune-pathogenetic mechanisms behind ASFV infection is still very limited. In this paper, we evaluated the haematological and immunological parameters of domestic pigs vaccinated with the ASFV Lv17/WB/Rie1 strain or its derived mutant Lv17/WB/Rie1/d110-11L and then challenged with virulent Armenia/07 ASFV. Circulating levels of C-reactive protein (CRP), 13 key cytokines and 11 haematological parameters were evaluated throughout the study. Lv17/WB/Rie1 triggered an inflammatory response, with increased levels of CRP and pro-inflammatory cytokines, and induced lymphopenia, thrombocytopenia and a decline in red blood cell (RBC) parameters, although this was transitory. Lv17/WB/Rie1/d110-11L triggered only transitory thrombocytopenia and a mild inflammatory reaction, with no increase in serum levels of pro-inflammatory cytokines, but it raised IL-1Ra levels. Both strains counteracted several adverse reactions elicited by virulent challenge, like thrombocytopenia, a decline in RBC parameters, and inflammation. Within this paper, we provided a deep portrayal of the impact of diverse ASFV strains on the domestic pig's immune system. A better understanding of these immune-pathological mechanisms would help to design suitable vaccines against this disease.

African Swine Fever Virus Infection and Cytokine Response In Vivo: An Update

African swine fever (ASF) is a hemorrhagic viral disease of domestic pigs and wild suids (all Sus scrofa) caused by the ASF virus (ASFV). The disease is spreading worldwide without control, threatening pig production due to the absence of licensed vaccine or commercially available treatments. A thorough understanding of the immunopathogenic mechanisms behind ASFV infection is required to better fight the disease. Cytokines are small, non-structural proteins, which play a crucial role in many aspects of the immune responses to viruses, including ASFV. Infection with virulent ASFV isolates often results in exacerbated immune responses, with increased levels of serum pro-inflammatory interleukins (IL-1α, IL-1β, IL-6), TNF and chemokines (CCL2, CCL5, CXCL10). Increased levels of IL-1, IL-6 and TNF are often detected in several tissues during acute ASFV infections and associated with lymphoid depletion, hemorrhages and oedemas. IL-1Ra is frequently released during ASFV infection to block further IL-1 activity, with its implication in ASFV immunopathology having been suggested. Increased levels of IFN-α and of the anti-inflammatory IL-10 seem to be negatively correlated with animal survival, whereas some correlation between virus-specific IFN-γ-producing cells and protection has been suggested in different studies where different vaccine candidates were tested, although future works should elucidate whether IFN-γ release by specific cell types is related to protection or disease development.

A Highly Effective African Swine Fever Virus Vaccine Elicits a Memory T Cell Response in Vaccinated Swine

African Swine Fever Virus (ASFV) is the causative agent of a highly contagious and lethal vector-borne disease in suids. Recently, a live attenuated virus strain, developed using the currently circulating, virulent Georgia strain (ASFV-G) with a single gene deletion (ASFV-G-ΔI177L), resulted in an effective vaccine. Nevertheless, protective immune response mechanisms induced by this candidate are poorly understood. In this study, Yorkshire crossbred swine intramuscularly vaccinated with 10⁶ 50% hemadsorption dose (HAD₅₀) of ASFV-G-ΔI177L or a vehicle control were challenged at 28 days post-inoculation (dpi) with 10² HAD₅₀ of ASFV-G. Analysis of purified peripheral blood mononuclear cells following inoculation and challenge revealed that CD4+, CD8+ and CD4+CD8+ central memory T cells (CD44+CD25-CD27-CD62L+CCR7+, T_cm) decreased significantly by 28 dpi in ASFV-G-ΔI177L-vaccinated swine compared to baseline and time-matched controls. Conversely, CD4+, CD8+ and CD4+CD8+ effector memory T cells (CD44+CD25-CD27-CD62-CCR7-, T_em) increased significantly among ASFV-G-ΔI177L-vaccined swine by 28 dpi compared to baseline and time-matched controls. Additionally, the percentage of natural killer (NK), CD4+ and CD4+CD8+ T_em and CD8+ T_cm and T_em positive for IFNγ increased significantly following inoculation, surpassing that of controls by 28 dpi or earlier. These results suggest that NK and memory T cells play a role in protective immunity and suggest that studying these cell populations may be a surrogate immunity marker in ASF vaccination.

Proteome Analysis of Swine Macrophages after Infection with Two Genotype II African Swine Fever Isolates of Different Pathogenicity

Since the introduction of a highly pathogenic genotype II isolate of the African swine fever virus (ASFV) into Georgia in 2007, African swine fever (ASF) has gone panzootic. Outbreaks have been reported in Europe, Asia and, more recently, Latin America. Thus, ASFV has become a major threat to the pig industry worldwide, as broadly applicable vaccines are not available. While the majority of ASFV strains show high virulence in domestic pigs and wild boar, variations within the ASFV genome have resulted in the emergence of attenuated strains with low or moderate virulence. However, the molecular basis of the differences in virulence has not yet been discovered. To reveal virulence-associated protein expression patterns, we analysed the proteomes of the natural target cells of ASFV, primary porcine macrophages, after infection with two genotype II ASFV strains displaying high (Armenia 2008) and moderate (Estonia 2014) virulence using quantitative mass spectrometry. Very similar expression patterns were observed for the viral genes, and any differences were limited to the deletions within the Estonia 2014 genome. In addition to the canonical ASFV proteins, twelve novel protein products from recently described transcripts were confirmed in both isolates. Pathway analyses showed that both isolates evoked a similar host proteome response, despite their difference in virulence. However, subtle differences in the manipulation of the proteins involved in the proinflammatory response mediated by the MAPK14/p38 signalling cascade were observed.

Blood parameters and pathological lesions in pigs experimentally infected with Vietnam's first isolated African swine fever virus

African swine fever virus (ASFV) is a notable virus and one of the most serious global threats to the pig industry. Improving awareness about host–virus interactions could facilitate the understanding of the disease pathogenesis. Therefore, we investigated changes in blood parameters, viral loads, and pathological changes in ASFV-inoculated pigs according to the time of death after the onset of viremia. For the analyses, the ASFV-infected pigs (n = 10) were divided into two groups (five pigs/group) according to their time of death after the onset of viremia. The blood cell count dynamics and serum biochemistry profiles were similar between the groups; however, viral load distribution was different. A comparison of the histopathological changes and immunohistochemistry results between the two groups indicated that the lymphoid system, particularly the spleen, was more damaged in the early stage of the disease than in the last stage. Additionally, the virus-induced lesions in other organs (liver and kidney) were more severe in the late stage than in the early stage. Our findings provide invaluable information on the characteristics of blood parameters and pathological lesions in pigs infected with the Asia-epidemic ASFV strain and the course of ASF, targeting internal organs in pigs. Overall, this study characterizes the host-pathogen interaction in ASFV infection, offering insight for the establishment of ASF control strategies.

The baseline immunological and hygienic status of pigs impact disease severity of African swine fever

African Swine Fever virus (ASFV) is a large double-enveloped DNA virus of the Asfarviridae family that causes a lethal hemorrhagic disease in domestic pigs and wild boars. Since 2007, a highly virulent genotype II strain has emerged and spread in Europe and South-East Asia, where millions of animals succumbed to the disease. Field- and laboratory-attenuated strains of ASFV cause highly variable clinical disease severity and survival, and mechanisms remain unclear. We hypothesized that the immunological and hygienic status of pigs is a determinant of ASF disease course. Here we compared the immunological profile at baseline and in response to ASFV infection in specific pathogen-free (SPF) and farm-raised Large White domestic pigs. At steady state, SPF pigs showed lower white blood cell counts and a lower basal inflammatory and antiviral transcriptomic profile compared to farm pigs, associated with profound differences in gut microbiome composition. After inoculation with a highly virulent ASFV genotype II strain (Armenia 2008), severe clinical signs, viremia and pro-inflammatory cytokines appeared sooner in SPF pigs, indicating a reduced capacity to control early virus replication. In contrast, during infection with an attenuated field isolate (Estonia 2014), SPF pigs presented a milder and shorter clinical disease with full recovery, whereas farm pigs presented severe protracted disease with 50% lethality. Interestingly, farm pigs showed higher production of inflammatory cytokines, whereas SPF pigs produced more anti-inflammatory IL-1ra early after infection and presented a stronger expansion of leukocytes in the recovery phase. Altogether, our data indicate that the hygiene-dependent innate immune status has a double-edge sword impact on immune responses in ASF pathogenesis. While the higher baseline innate immune activity helps the host in reducing initial virus replication, it promotes immunopathological cytokine responses, and delays lymphocyte proliferation after infection with an attenuated strain. Such effects should be considered for live vaccine development and vigilance.

African Swine Fever Control and Prevention: An Update on Vaccine Development

African swine fever (ASF) is a lethal and highly contagious viral disease of domestic and wild pigs, listed as a notifiable disease reported to the World Organization for Animal Health (OIE). Despite its limited host range and absent zoonotic potential, the socio-economic and environmental impact of ASF is very high, representing a serious threat to the global swine industry and the many stakeholders involved. Currently, only control and eradication measures based mainly on early detection and strict stamping-out policies are available, however, the rapid spread of the disease in new countries, and in new regions in countries already affected, show these strategies to be lacking. In this review, we discuss approaches to ASF vaccinology, with emphasis on the advances made over the last decade, including the development of virulence-associated gene deleted strains such as the very promising ASFV-G-ΔI177L/ΔLVR, that replicates efficiently in a stable porcine epithelial cell line, and the cross-protecting BA71ΔCD2 capable of stably growing in the commercial COS-1 cell line, or the naturally attenuated Lv17/WB/Rie1 which shows solid protection in wild boar. We also consider the key constraints involved in the scale-up and commercialization of promising live attenuated and virus-vectored vaccine candidates, namely cross-protection, safety, lack of suitable animal models, compatibility with wildlife immunization, availability of established and licensed cell lines, and differentiating infected from vaccinated animals (DIVA) strategy.

Cellular and Humoral Immune Responses after Immunisation with Low Virulent African Swine Fever Virus in the Large White Inbred Babraham Line and Outbred Domestic Pigs

African swine fever virus is currently present in all of the world’s continents apart from Antarctica, and efforts to control the disease are hampered by the lack of a commercially available vaccine. The Babraham large white pig is a highly inbred line that could represent a powerful tool to improve our understanding of the protective immune responses to this complex pathogen; however, previous studies indicated differential vaccine responses after the African swine fever virus challenge of inbred minipigs with different swine leukocyte antigen haplotypes. Lymphocyte numbers and African swine fever virus-specific antibody and T-cell responses were measured in inbred and outbred animals after inoculation with a low virulent African swine fever virus isolate and subsequent challenge with a related virulent virus. Surprisingly, diminished immune responses were observed in the Babraham pigs when compared to the outbred animals, and the inbred pigs were not protected after challenge. Recovery of Babraham pigs after challenge weakly correlated with antibody responses, whereas protective responses in outbred animals more closely correlated with the T-cell response. The Babraham pig may, therefore, represent a useful model for studying the role of antibodies in protection against the African swine fever virus.

Development of a Monoclonal Antibody to Pig CD69 Reveals Early Activation of T Cells in Pig after PRRSV and ASFV Infection

The CD69 molecule, as an early activation marker of lymphocytes, is often used to assess the activation of cellular immunity. However, for pigs, an anti-pig CD69 antibody is not yet available for this purpose after infection or vaccination. In this study, a monoclonal antibody (mAb) against pig CD69 was produced by peptide immunization and hybridoma technique. One mAb (5F12) showed good reactivity with pig CD69 that was expressed in transfected-HEK-293T cells and on mitogen-activated porcine peripheral blood mononuclear cells (PBMCs) by indirect immunofluorescence assay and flow cytometry. This mAb did not cross-react with activated lymphocytes from mouse, bovine, and chicken. Epitope mapping showed that the epitope recognized by this mAb was located at amino acid residues 147–161 of pig CD69. By conjugating with fluorochrome, this mAb was used to detect the early activation of lymphocytes in PRRSV- and ASFV-infected pigs by flow cytometry. The results showed that PRRSV infection induced the dominant activation of CD4 T cells in mediastinal lymph nodes and CD8 T cells in the spleen at 14 days post-infection, in terms of CD69 expression. In an experiment on ASFV infection, we found that ASFV infection resulted in the early activation of NK cells, B cells, and distinct T cell subsets with variable magnitude in PBMCs, spleen, and submandibular lymph nodes. Our study revealed an early event of lymphocyte and T cell activation after PRRSV and ASFV infections and provides an important immunological tool for the in-depth analysis of cellular immune response in pigs after infection or vaccination.

Adenovirus-Vectored African Swine Fever Virus pp220 Induces Robust Antibody, IFN-γ, and CTL Responses in Pigs

African Swine Fever Virus (ASFV) poses a serious threat to the pork industry worldwide; however, there is no safe vaccine or treatment available. The development of an efficacious subunit vaccine will require the identification of protective antigens. The ASFV pp220 polyprotein is essential for virus structural integrity. This polyprotein is processed to generate p5, p34, p14, p37, and p150 individual proteins. Immunization of pigs with a cocktail of adenoviruses expressing the proteins induced significant IgG, IFN-γ-secreting cells, and cytotoxic T lymphocyte responses. Four predicted SLA-I binding nonamer peptides, namely p34161−169, p37859−867, p1501363−1371, and p1501463−1471, recalled strong IFN-γ+ PBMC and splenocyte responses. Notably, peptide p34161−169 was recognized by PBMCs isolated from 7/10 pigs and by splenocytes isolated from 8/10 pigs. Peptides p37859−867 and p1501363−1371 stimulated recall IFN-γ+ responses in PBMCs and splenocytes isolated from 8/10 pigs, whereas peptide p1501463−1471 recalled responses in PBMCs and splenocytes isolated from 7/10 to 9/10 pigs, respectively. The results demonstrate that the pp220 polyprotein contains multiple epitopes that induce robust immune responses in pigs. Importantly, these epitopes are 100% conserved among different ASFV genotypes and were predicted to bind multiple SLA-I alleles. The outcomes suggest that pp220 is a promising candidate for inclusion in a prototype subunit vaccine.

ASF -survivors’ sera do not inhibit African swine fever virus replication in vitro

Introduction

African swine fever virus (ASFV) causes one of the most dangerous diseases of pigs and wild boar – African swine fever (ASF). Since its second introduction into Europe (in 2007), the disease has been spreading consistently, and now ASF-free European countries are at risk. Complex interactions between the host’s immune system and the virus have long prevented the development of a safe vaccine against ASF. This study analysed the possibility of neutralisation of the ASFV in vitro by sera collected from ASF-survivor animals.

Material and Methods

Two pig and three wild boar serum samples were collected from previously selected potential ASF survivors. All sera presented high antibody titres (>5 log₁₀/mL). Primary alveolar macrophages were cultured in growth medium containing 10% and 20% concentrations of selected sera and infected with a haemadsorbing ASFV strain (Pol18_28298_O111, genotype II). The progress of infection was investigated under a light microscope by observing the cytopathic effect (CPE) and the haemadsorption phenomenon. Growth kinetics were investigated using a real-time PCR assay.

Results

Haemadsorption inhibition was detected in the presence of almost all selected sera; however, the inhibition of virus replication in vitro was excluded. In all samples, a CPE and decreasing quantification cycle values of the viral DNA were found.

Conclusion

Anti-ASFV antibodies alone are not able to inhibit virus replication. Interactions between the humoral and cellular immune response which effectively combat the disease are implicated in an ASF-survivor’s organism.

Adaptive Cellular Immunity against African Swine Fever Virus Infections

African swine fever virus (ASFV) remains a threat to global pig populations. Infections with ASFV lead to a hemorrhagic disease with up to 100% lethality in Eurasian domestic and wild pigs. Although myeloid cells are the main target cells for ASFV, T cell responses are impacted by the infection as well. The complex responses remain not well understood, and, consequently, there is no commercially available vaccine. Here, we review the current knowledge about the induction of antiviral T cell responses by cells of the myeloid lineage, as well as T cell responses in infected animals, recent efforts in vaccine research, and T cell epitopes present in ASFV.

Evaluation of Cellular Immunity with ASFV Infection by Swine Leukocyte Antigen (SLA)-Peptide Tetramers

African swine fever virus (ASFV) causes acute hemorrhagic fever in domestic pigs and wild boars, resulting in incalculable economic losses to the pig industry. As the mechanism of viral infection is not clear, protective antigens have not been discovered or identified. In this study, we determined that the p30, pp62, p72, and CD2v proteins were all involved in the T cell immune response of live pigs infected with ASFV, among which p72 and pp62 proteins were the strongest. Panoramic scanning was performed on T cell epitopes of the p72 protein, and three high-frequency positive epitopes were selected to construct a swine leukocyte antigen (SLA)-tetramer, and ASFV-specific T cells were detected. Subsequently, the specific T cell and humoral immune responses of ASFV-infected pigs and surviving pigs were compared. The results demonstrate that the specific T cellular immunity responses gradually increased during the infection and were higher than that in the surviving pigs in the late stages of infection. The same trend was observed in specific humoral immune responses, which were highest in surviving pigs. In general, our study provides key information for the exploration of ASFV-specific immune responses and the development of an ASFV vaccine.

Local and Systemic T Cell Immunity in Fighting Pig Viral and Bacterial Infections

T cells are an essential component of the adaptive immune system. Over the last 15 years, a constantly growing toolbox with which to study T cell biology in pigs has allowed detailed investigations on these cells in various viral and bacterial infections. This review provides an overview on porcine CD4, CD8, and γδ T cells and the current knowledge on the differentiation of these cells following antigen encounter. Where available, the responses of these cells to viral infections like porcine reproductive and respiratory syndrome virus, classical swine fever virus, swine influenza A virus, and African swine fever virus are outlined. In addition, knowledge on the porcine T cell response to bacterial infections like Actinobacillus pleuropneumoniae and Salmonella Typhimurium is reviewed. For CD4 T cells, the response to the outlined infections is reflected toward the Th1/Th2/Th17/Tfh/Treg paradigm for functional differentiation. Expected final online publication date for the Annual Review of Animal Biosciences, Volume 10 is February 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Regulation and Evasion of Host Immune Response by African Swine Fever Virus

African swine fever (ASF) is an acute lethal hemorrhagic viral disease in domestic pigs and wild boars; is widely epidemic in Africa, Europe, Asia, and Latin America; and poses a huge threat to the pig industry worldwide. ASF is caused by the infection of the ASF virus (ASFV), a cytoplasmic double-stranded DNA virus belonging to the Asfarviridae family. Here, we review how the virus regulates the host immune response and its mechanisms at different levels, including interferon modulation, inflammation, apoptosis, antigen presentation, and cellular immunity.

African Swine Fever in Wild Boar in Europe-A Review

The introduction of genotype II African swine fever (ASF) virus, presumably from Africa into Georgia in 2007, and its continuous spread through Europe and Asia as a panzootic disease of suids, continues to have a huge socio-economic impact. ASF is characterized by hemorrhagic fever leading to a high case/fatality ratio in pigs. In Europe, wild boar are especially affected. This review summarizes the currently available knowledge on ASF in wild boar in Europe. The current ASF panzootic is characterized by self-sustaining cycles of infection in the wild boar population. Spill-over and spill-back events occur from wild boar to domestic pigs and vice versa. The social structure of wild boar populations and the spatial behavior of the animals, a variety of ASF virus (ASFV) transmission mechanisms and persistence in the environment complicate the modeling of the disease. Control measures focus on the detection and removal of wild boar carcasses, in which ASFV can remain infectious for months. Further measures include the reduction in wild boar density and the limitation of wild boar movements through fences. Using these measures, the Czech Republic and Belgium succeeded in eliminating ASF in their territories, while the disease spread in others. So far, no vaccine is available to protect wild boar or domestic pigs reliably against ASF.

Synergistic effect of the responses of different tissues against African swine fever virus

African swine fever is an acute, haemorrhagic fever and contagious disease of pigs caused by African swine fever virus (ASFV), which has a great impact on the pig farming industry and related international trade. Understanding the response processes of various tissues in pigs after ASFV infection may help to address current major concerns, such as the exploration of key genes for vaccine development, the cooperative mechanism of the host response and the possibility of establishing active herd immunity. ASFV is able to infect core tissues and is associated with acute death. RNA and protein samples were obtained and verified from five tissues, including the lung, spleen, liver, kidney and lymph nodes. Multiple duplicate samples were quantitatively analyzed by corresponding transcriptomic and proteomic comparison. The results showed that different tissues cooperated in responses to ASFV infection and coordinated the defence against ASFV in the form of an inflammatory cytokine storm and interferon activation. The lung and spleen were mainly involved (dominant) in the innate immune response pathway; the liver and kidney were involved in the metabolic regulatory pathway and the inflammatory response; and the lymph nodes cooperated with the liver to complete energy metabolism regulation. The key pathways and responsive genes in each tissue of the contracted pigs were comprehensively mapped by infectomics, providing further evidence to investigate the complicated tie between ASFV and host cells.

Generation and first characterization of TRDC-knockout pigs lacking γδ T cells

The TRDC-locus encodes the T cell receptor delta constant region, one component of the γδ T cell receptor which is essential for development of γδ T cells. In contrast to peptide recognition by αβ T cells, antigens activating γδ T cells are mostly MHC independent and not well characterized. Therefore, the function of γδ T cells and their contribution to protection against infections is still unclear. Higher numbers of circulating γδ T cells compared to mice, render the pig a suitable animal model to study γδ T cells. Knocking-out the porcine TRDC-locus by intracytoplasmic microinjection and somatic cell nuclear transfer resulted in healthy living γδ T cell deficient offspring. Flow cytometric analysis revealed that TRDC-KO pigs lack γδ T cells in peripheral blood mononuclear cells (PBMC) and spleen cells. The composition of the remaining leucocyte subpopulations was not affected by the depletion of γδ T cells. Genome-wide transcriptome analyses in PBMC revealed a pattern of changes reflecting the impairment of known or expected γδ T cell dependent pathways. Histopathology did not reveal developmental abnormalities of secondary lymphoid tissues. However, in a vaccination experiment the KO pigs stayed healthy but had a significantly lower neutralizing antibody titer as the syngenic controls.

Blood Counts, Biochemical Parameters, Inflammatory, and Immune Responses in Pigs Infected Experimentally with the African Swine Fever Virus Isolate Pol18_28298_O111

This study aimed to indicate the influence of infection caused by genotype II African swine fever virus (ASFV)–isolate Pol18_28298_O111, currently circulating in Poland, on blood counts, biochemical parameters, as well as inflammatory and immune responses. Blood and sera collected from 21 domestic pigs infected intranasally with different doses of virulent ASFV were analysed. The infection led to variable changes in blood counts depending on the stage of the disease with a tendency towards leukopenia and thrombocytopenia. The elevated C-reactive protein (CRP) concentrations and microscopic lesions in organs confirmed the development of the inflammation process, which also resulted in an increased level of biochemical markers such as: Aspartate transaminase (AST), creatine kinase (CK), creatinine, and urea. Antibodies could be detected from 9 to 18 days post infection (dpi). Two survivors presented the highest titer of antibodies (>5 log₁₀/mL) with a simultaneous increase in the lymphocyte T (CD3+) percentage–revealed by flow cytometry. Results confirmed a progressive inflammatory process occurring during the ASFV infection, which may lead to multiple organs failure and death of the majority of affected animals.

T-cell responses in domestic pigs and wild boar upon infection with the moderately virulent African swine fever virus strain 'Estonia2014'

Infection with African swine fever virus (ASFV) causes a highly lethal haemorrhagic disease in domestic and Eurasian wild pigs. Thus, it is a major threat to pig populations worldwide and a cause of substantial economic losses. Recently, less virulent ASFV strains emerged naturally, which showed higher experimental virulence in wild boar than in domestic pigs. The reason for this difference in disease progression and outcome is unclear but likely involves different immunological responses. Unfortunately, besides the importance of CD8α⁺ lymphocytes, little is known about the immune responses against ASFV in suids. Against this background, we used a multicolour flow cytometry platform to investigate the T-cell responses in wild boar and domestic pigs after infection with the moderately virulent ASFV strain 'Estonia2014' in two independent trials. CD4^- /CD8α⁺ and CD4⁺ /CD8α⁺ αβ T-cell frequencies increased in both subspecies in various tissues, but CD8α⁺ γδ T cells differentiated and responded in wild boar only. Proliferation in CD8α⁺ T cells was found 10 days post infectionem only. Frequencies of T-bet⁺ T cells increased in wild boar but not in domestic pigs. Of note, we found a considerable loss of perforin expression in cytotoxic T cells, 5 and 7 dpi. Both subspecies established a regulatory T-cell response 10 dpi. In domestic pigs, we show increasing levels of ICOS⁺ and CD8α⁺ invariant Natural Killer T cells. These disparities in T-cell responses might explain some of the differences in disease progression in wild boar and domestic pigs and should pave the way for future studies.

Cytokine Storm in Domestic Pigs Induced by Infection of Virulent African Swine Fever Virus

African swine fever, caused by African swine fever virus (ASFV), is a highly contagious hemorrhagic disease of domestic pigs. The current continent-wide pandemic has persisted for over 10 years, and its economy-devastating effect was highlighted after spreading to China, which possesses half of the world pig industry. So far, development of an effective and safe vaccine has not been finished largely due to the knowledge gaps in pathogenesis and immunology, particularly the role of cytokines in the host's immune response. Therefore, we performed experiments in domestic pigs to analyze the kinetics of representative circulating interferons (IFNs), interleukins (ILs), growth factors, tumor necrosis factors (TNFs), and chemokines induced by infection of type II virulent ASFV SY18. Pigs infected with this Chinese prototypical isolate developed severe clinical manifestations mostly from 3 days post inoculation (dpi) and died from 7 to 8 dpi. Serum analysis revealed a trend of robust and sustained elevation of pro-inflammatory cytokines including TNF-α, IFN-α, IL-1β, IL-6, IL-8, IL-12, IL-18, RANTES (regulated upon activation, normal T cell expressed and secreted), and IFN-γ-induced protein 10 (IP-10) from 3 dpi, but not the anti-inflammatory cytokines IL-10 and transforming growth factor-β (TGF-β). Moreover, secondary drastic increase of the levels of TNF-α, IL-1β, IL-6, and IL-8, as well as elevated IL-10, was observed at the terminal phase of infection. This pattern of cytokine secretion clearly drew an image of a typical cytokine storm characterized by delayed and dysregulated initiation of the secretion of pro-inflammatory cytokine and imbalanced pro- and anti-inflammatory response, which paved a way for further understanding of the molecular basis of ASFV pathogenesis.

Computational Analysis of African Swine Fever Virus Protein Space for the Design of an Epitope-Based Vaccine Ensemble

African swine fever virus is the etiological agent of African swine fever, a transmissible severe hemorrhagic disease that affects pigs, causing massive economic losses. There is neither a treatment nor a vaccine available, and the only method to control its spread is by extensive culling of pigs. So far, classical vaccine development approaches have not yielded sufficiently good results in terms of concomitant safety and efficacy. Nowadays, thanks to advances in genomic and proteomic techniques, a reverse vaccinology strategy can be explored to design alternative vaccine formulations. In this study, ASFV protein sequences were analyzed using an in-house pipeline based on publicly available immunoinformatic tools to identify epitopes of interest for a prospective vaccine ensemble. These included experimentally validated sequences from the Immune Epitope Database, as well as de novo predicted sequences. Experimentally validated and predicted epitopes were prioritized following a series of criteria that included evolutionary conservation, presence in the virulent and currently circulating variant Georgia 2007/1, and lack of identity to either the pig proteome or putative proteins from pig gut microbiota. Following this strategy, 29 B-cell, 14 CD4⁺ T-cell and 6 CD8⁺ T-cell epitopes were selected, which represent a starting point to investigating the protective capacity of ASFV epitope-based vaccines.

Comparative Pathology of Domestic Pigs and Wild Boar Infected with the Moderately Virulent African Swine Fever Virus Strain "Estonia 2014"

Endemically infected European wild boar are considered a major reservoir of African swine fever virus in Europe. While high lethality was observed in the majority of field cases, strains of moderate virulence occurred in the Baltic States. One of these, "Estonia 2014", led to a higher number of clinically healthy, antibody-positive animals in the hunting bag of North-Eastern Estonia. Experimental characterization showed high virulence in wild boar but moderate virulence in domestic pigs. Putative pathogenic differences between wild boar and domestic pigs are unresolved and comparative pathological studies are limited. We here report on a kinetic experiment in both subspecies. Three animals each were euthanized at 4, 7, and 10 days post infection (dpi). Clinical data confirmed higher virulence in wild boar although macroscopy and viral genome load in blood and tissues were comparable in both subspecies. The percentage of viral antigen positive myeloid cells tested by flow cytometry did not differ significantly in most tissues. Only immunohistochemistry revealed consistently higher viral antigen loads in wild boar tissues in particular 7 dpi, whereas domestic pigs already eliminated the virus. The moderate virulence in domestic pigs could be explained by a more effective viral clearance.