Immunization with matrix-, nucleoprotein and neuraminidase protects against H3N2 influenza challenge in pH1N1 pre-exposed pigs

There is an urgent need for influenza vaccines providing broader protection that may decrease the need for annual immunization of the human population. We investigated the efficacy of heterologous prime boost immunization with chimpanzee adenovirus (ChAdOx2) and modified vaccinia Ankara (MVA) vectored vaccines, expressing conserved influenza virus nucleoprotein (NP), matrix protein 1 (M1) and neuraminidase (NA) in H1N1pdm09 pre-exposed pigs. We compared the efficacy of intra-nasal, aerosol and intra-muscular vaccine delivery against H3N2 influenza challenge. Aerosol prime boost immunization induced strong local lung T cell and antibody responses and abrogated viral shedding and lung pathology following H3N2 challenge. In contrast, intramuscular immunization induced powerful systemic responses and weak local lung responses but also abolished lung pathology and reduced viral shedding. These results provide valuable insights into the development of a broadly protective influenza vaccine in a highly relevant large animal model and will inform future vaccine and clinical trial design.

Low Dose Pig Anti-Influenza Virus Monoclonal Antibodies Reduce Lung Pathology but Do Not Prevent Virus Shedding

We have established the pig, a large natural host animal for influenza, with many physiological similarities to humans, as a robust model for testing the therapeutic potential of monoclonal antibodies (mAbs). In this study we demonstrated that prophylactic intravenous administration of 15 mg/kg of porcine mAb pb18, against the K160-163 site of the hemagglutinin, significantly reduced lung pathology and nasal virus shedding and eliminated virus from the lung of pigs following H1N1pdm09 challenge. When given at 1 mg/kg, pb18 significantly reduced lung pathology and lung and BAL virus loads, but not nasal shedding. Similarly, when pb18 was given in combination with pb27, which recognized the K130 site, at 1 mg/kg each, lung virus load and pathology were reduced, although without an apparent additive or synergistic effect. No evidence for mAb driven virus evolution was detected. These data indicate that intravenous administration of high doses was required to reduce nasal virus shedding, although this was inconsistent and seldom complete. In contrast, the effect on lung pathology and lung virus load is consistent and is also seen at a one log lower dose, strongly indicating that a lower dose might be sufficient to reduce severity of disease, but for prevention of transmission other measures would be needed.

Distinct immune responses and virus shedding in pigs following aerosol, intra-nasal and contact infection with pandemic swine influenza A virus, A(H1N1)09

Influenza virus infection in pigs is a major farming problem, causing considerable economic loss and posing a zoonotic threat. In addition the pig is an excellent model for understanding immunity to influenza viruses as this is a natural host pathogen system. Experimentally, influenza virus is delivered to pigs intra-nasally, by intra-tracheal instillation or by aerosol, but there is little data comparing the outcome of different methods. We evaluated the shedding pattern, cytokine responses in nasal swabs and immune responses following delivery of low or high dose swine influenza pdmH1N1 virus to the respiratory tract of pigs intra-nasally or by aerosol and compared them to those induced in naturally infected contact pigs. Our data shows that natural infection by contact induces remarkably high innate and adaptive immune response, although the animals were exposed to a very low virus dose. In contacts, the kinetics of virus shedding were slow and prolonged and more similar to the low dose directly infected animals. In contrast the cytokine profile in nasal swabs, antibody and cellular immune responses of contacts more closely resemble immune responses in high dose directly inoculated animals. Consideration of these differences is important for studies of disease pathogenesis and assessment of vaccine protective efficacy.

The B-cell response to foot-and-mouth-disease virus in cattle following vaccination and live-virus challenge

Antibodies play a pivotal role against viral infection, and maintenance of protection is dependent on plasma and memory B-cells. Understanding antigen-specific B-cell responses in cattle is essential to inform future vaccine design. We have previously defined T-cell-dependent and -independent B-cell responses in cattle, as a prelude to investigating foot-and-mouth-disease-virus (FMDV)-specific B-cell responses. In this study, we have used an FMDV O-serotype vaccination (O₁-Manisa or O SKR) and live-virus challenge (FMDV O SKR) to investigate the homologous and heterologous B-cell response in cattle following both vaccination and live-virus challenge. The FMDV O-serotype vaccines were able to induce a cross-reactive plasma-cell response, specific for both O₁-Manisa and O SKR, post-vaccination. Post-FMDV O SKR live-virus challenge, the heterologous O₁-Manisa vaccination provided cross-protection against O SKR challenge and cross-reactive O SKR-specific plasma cells were induced. However, vaccination and live-virus challenge were not able to induce a detectable FMDV O-serotype-specific memory B-cell response in any of the cattle. The aim of new FMDV vaccines should be to induce memory responses and increased duration of immunity in cattle.

Assessment of T-dependent and T-independent immune responses in cattle using a B cell ELISPOT assay

Understanding the mechanisms that maintain protective antibody levels after immunisation is important for vaccine design. In this study, we have determined the kinetics of plasma and memory B cells detectable in the blood of cattle immunised with model T-dependent or T-independent antigens. Immunisation with the T-D antigen resulted in an expansion of TNP-specific plasma cells post-TNP primary and booster immunisations, which was associated with increased titres of TNP-specific IgG antibodies. Although no TNP-specific memory B cells were detected in the T-D group following the primary immunisation, we detected an increase in the number of TNP-specific memory B cells post-TNP boost. In contrast, no TNP-specific plasma or memory B cells were detected after primary or secondary immunisation with the T-I antigen. We then investigated if immunisation with a third party antigen (tetanus toxin fragment C, TTC) would result in a bystander stimulation and increase the number of TNP-specific plasma and memory B cells in the T-D and/or T-I group. TTC immunisation in the T-D group resulted in a small increase in the number of TNP-specific plasma cells post-TTC primary immunisation and boost, and in an increase in the number of TNP-specific memory B cells post-TTC boost. This bystander effect was not observed in the animals previously immunised with the T-I antigen. In conclusion, the present study characterised for the first time the B cell response in cattle to immunisation with T-D and T-I antigens and showed that bystander stimulation of an established T-D B cell memory response may occur in cattle.

CD4+ T-cell responses to foot-and-mouth disease virus in vaccinated cattle

We have performed a series of studies to investigate the role of CD4⁺ T-cells in the immune response to foot-and-mouth disease virus (FMDV) post-vaccination. Virus neutralizing antibody titres (VNT) in cattle vaccinated with killed FMD commercial vaccine were significantly reduced and class switching delayed as a consequence of rigorous in vivo CD4⁺ T-cell depletion. Further studies were performed to examine whether the magnitude of T-cell proliferative responses correlated with the antibody responses. FMD vaccination was found to induce T-cell proliferative responses, with CD4⁺ T-cells responding specifically to the FMDV antigen. In addition, gamma interferon (IFN-γ) was detected in the supernatant of FMDV antigen-stimulated PBMC and purified CD4⁺ T-cells from vaccinated cattle. Similarly, intracellular IFN-γ could be detected specifically in purified CD4⁺ T-cells after restimulation. It was not possible to correlate in vitro proliferative responses or IFN-γ production of PBMC with VNT, probably as a consequence of the induction of T-independent and T-dependent antibody responses and antigen non-specific T-cell responses. However, our studies demonstrate the importance of stimulating CD4⁺ T-cell responses for the induction of optimum antibody responses to FMD-killed vaccines.

Immune responses in pigs vaccinated with adjuvanted and non-adjuvanted A(H1N1)pdm/09 influenza vaccines used in human immunization programmes

Following the emergence and global spread of a novel H1N1 influenza virus in 2009, two A(H1N1)pdm/09 influenza vaccines produced from the A/California/07/09 H1N1 strain were selected and used for the national immunisation programme in the United Kingdom: an adjuvanted split virion vaccine and a non-adjuvanted whole virion vaccine. In this study, we assessed the immune responses generated in inbred large white pigs (Babraham line) following vaccination with these vaccines and after challenge with A(H1N1)pdm/09 virus three months post-vaccination. Both vaccines elicited strong antibody responses, which included high levels of influenza-specific IgG1 and haemagglutination inhibition titres to H1 virus. Immunisation with the adjuvanted split vaccine induced significantly higher interferon gamma production, increased frequency of interferon gamma-producing cells and proliferation of CD4⁻CD8⁺ (cytotoxic) and CD4⁺CD8⁺ (helper) T cells, after in vitro re-stimulation. Despite significant differences in the magnitude and breadth of immune responses in the two vaccinated and mock treated groups, similar quantities of viral RNA were detected from the nasal cavity in all pigs after live virus challenge. The present study provides support for the use of the pig as a valid experimental model for influenza infections in humans, including the assessment of protective efficacy of therapeutic interventions.

Cattle remain immunocompetent during the acute phase of foot-and-mouth disease virus infection

Infection of cattle with foot-and-mouth disease virus (FMDV) results in the development of long-term protective antibody responses. In contrast, inactivated antigen vaccines fail to induce long-term protective immunity. Differences between susceptible species have also been observed during infection with FMDV, with cattle often developing persistent infections whilst pigs develop more severe symptoms and excrete higher levels of virus. This study examined the early immune response to FMDV in naïve cattle after in-contact challenge. Cattle exposed to FMDV were found to be viraemic and produced neutralising antibody, consistent with previous reports. In contrast to previous studies in pigs these cattle did not develop leucopenia, and the proliferative responses of peripheral blood mononuclear cells to either mitogen or third party antigen were not suppressed. Low levels of type 1 interferon and IL-10 were detected in the circulation. Taken together, these results suggest that there was no generalised immunosuppression during the acute phase of FMDV infection in cattle.

Longevity of protection in cattle following immunisation with emergency FMD A22 serotype vaccine from the UK strategic reserve

To determine the longevity of protective immunity following a single administration of emergency vaccine, and establish whether the immune response could be enhanced by increasing the antigen payload even further, cattle were vaccinated with an A22 Iraq vaccine containing either 1x antigen payload (field dose) or 5x antigen payload. Six months post-immunisation all cattle received a homologous virus challenge. The magnitude of the virus neutralising antibody response elicited was consistent with the response to similarly formulated A serotype vaccines with a PD(50) greater than 32. All the vaccinated cattle, regardless of antigen payload, were protected from clinical disease following challenge although some cattle in both groups became sub-clinically infected. We conclude that immunisation with a single inoculation of vaccine from the UK emergency reserve can protect cattle from clinical disease for at least 6 months post-vaccination and that a boost may be unnecessary in an outbreak situation. Some animals may become sub-clinically infected but this is likely to be dependent on the severity of challenge. The study confirmed that a booster at 21 days post-vaccination was not necessary to maintain a cell-mediated response in cattle for 6 months. No increased benefits were recognised by increasing the antigen payload of this vaccine 5x.

A quantitative assessment of primary and secondary immune responses in cattle using a B cell ELISPOT assay

The aim of the study was to build a comprehensive picture of the appearance in the blood stream of Ag-specific plasma cells and memory B cells in the bovine model. For this purpose, we have developed a method allowing the detection and quantification of both cell types within individual calves immunised with ovalbumin. During the primary response, we detected a burst of ovalbumin-specific plasma cells at days 6 and 7 post-immunisation, which was followed by the production of specific Ab, whereas a gradual increase of memory B cells was only detected from day 15. As expected, a boost immunisation performed 7 weeks later induced a quicker and stronger secondary response. Indeed, a burst of plasma cells was detected in the blood at days 3 and 4, which was followed by a strong increase in Ab titres. Furthermore, a burst of memory B cells, and not a gradual increase, was detected at days 5 and 6 post-boost immunisation. Importantly, we showed a strong correlation between the anti-ovalbumin-specific IgG titres detected 5 months after secondary immunisation and the plasma cell numbers detected in the blood at the peak response after secondary immunisation. The detection and quantification of plasma cells following an immunisation/vaccination strategy could constitute a very effective means for predicting the magnitude and longevity of an Ab response.

Identification of a novel foot-and-mouth disease virus specific T-cell epitope with immunodominant characteristics in cattle with MHC serotype A31

To identify foot-and-mouth disease virus (FMDV) specific T-cell epitopes within the entire polyprotein sequence of the virus, 442 overlapping pentadecapeptides were tested in proliferation assays using lymphocytes from cattle experimentally infected with FMDV. Four months post-infection cells from all investigated animals (n = 4) responded by proliferation and interferon-gamma production to a peptide located on the structural protein 1D (VP1), amino acid residues 66-80. Major histocompatibility complex (MHC) serotyping of the investigated cattle indicated that all animals shared the MHC serotype A31 which comprises the class II allele DRB3 0701. This may explain the common recognition of this newly discovered epitope. Responses to other peptides could only be observed in one animal and rapidly declined during the time course of the study. These observations point to an immunodominant role of this epitope located on the protein 1D in cattle with MHC serotype A31.

Workshop cluster 1, a γδ T cell specific receptor is phosphorylated and down regulated by activation induced Src family kinase activity

Workshop cluster 1(+) gamma delta (WC1(+)gammadelta) T cells have been shown to play important roles in the immune response to infections. WC1 is a transmembrane glycoprotein, uniquely expressed on the surface of gammadelta T cells of ruminants and pigs. A role for WC1 in inducing a reversible growth arrest of gammadelta T cells has been previously demonstrated. WC1-induced growth inhibition has been shown to be overcome following gammadelta T cell activation with Concanavalin A (Con A). However, molecular mechanism(s) by which WC1 signalling might be modulated following activation have not been elucidated. In this paper we show that Con A activation of bovine lymphocytes induces the tyrosine phosphorylation of WC1 in a Src-family kinase-dependent manner. Src family kinases also phosphorylated WC1 in a COS-7 co-transfection system. Furthermore, a glutathione-S-transferase (GST)-WC1 cytoplasmic domain fusion protein was directly phosphorylated by recombinant Lck (rLck) in vitro. The Y(1303) of WC1 was identified by mutational analysis as the only one of the five WC1 tyrosine residues to be critical for Src family phosphorylation. The importance of activation-induced Src family activity for WC1 function was investigated with the Src-family specific inhibitor PP2. These studies show that the surface levels of WC1 are down regulated in a Src-family-dependent manner following activation of bovine lymphocytes. Down regulation of surface WC1 was accompanied by a Src-family-dependent accumulation of intracellular WC1. These data show that WC1 is modulated by activation-induced tyrosine phosphorylation thus providing a new insight into the signalling mechanisms by which WC1 and gammadelta T cell activation are regulated in this important and unique cell population.

The glycosylation pattern of baculovirus expressed envelope protein E2 affects its ability to prevent infection with bovine viral diarrhoea virus

We have investigated the role of glycosylation of the envelope glycoprotein E2 of bovine viral diarrhoea virus (BVDV), produced in insect cells, in BVDV infection. When amino acids predicated to code for the C-terminal N-linked glycosylation site were mutated the resulting protein was less efficient than wild type protein at preventing infection of susceptible cells with BVDV. In addition, mutational analysis showed that a further two predicted N-terminal N-linked glycosylation sites of E2 are required for efficient production of recombinant protein.

Identification of a cell population that produces alpha/beta interferon in vitro and in vivo in response to noncytopathic bovine viral diarrhea virus

In vitro infection of bovine cells of many origins with the cytopathogenic bovine viral diarrhea virus (cpBVDV) results in the induction of alpha/beta interferon (IFN-alpha/beta), whereas noncytopathogenic BVDV (ncpBVDV) isolates have been shown not to induce IFN-alpha/beta in vitro. Similarly, cpBVDV induces IFN-alpha/beta in the early bovine fetus, but ncpBVDV does not. However, acute infection of naive cattle with ncpBVDV results in IFN-alpha/beta production. In this study, we identified and characterized a minor population of cells, present in lymph nodes that produce IFN-alpha in response to ncpBVDV. These cells expressed the myeloid markers CD14, CD11b, and CD172a but did not express CD4 and CD45RB. We also established that these cells produced IFN-alpha in the absence of detectable productive infection.

Aspects of the innate and adaptive immune responses to acute infections with BVDV

The immune response can be divided into innate and adaptive components that synergise to effect the clearance of pathogens. Recently, it has been realised that these arms of the immune system do not act independently, the magnitude and quality of the adaptive response is dependent on signals derived from the innate response. Here, we review the innate immune responses to bovine viral diarrhoea virus infections of cattle and relate these changes to immunosuppression and the subsequent development of the adaptive immune response.

Differential effects of bovine viral diarrhoea virus on monocytes and dendritic cells

Various pathogens have been shown to infect antigen-presenting cells and affect their capacity to interact with and stimulate T-cell responses. We have used an antigenically identical pair of non-cytopathic (ncp) and cytopathic (cp) bovine viral diarrhoea virus (BVDV) isolates to determine how the two biotypes affect monocyte and dendritic cell (DC) function. We have shown that monocytes and DCs are both susceptible to infection with ncp BVDV and cp BVDV in vitro. In addition, monocytes infected with ncp BVDV were compromised in their ability to stimulate allogeneic and memory CD4(+) T cell responses, but DCs were not affected. This was not due to down-regulation of a number of recognized co-stimulatory molecules including CD80, CD86 and CD40. Striking differences in the response of the two cell types to infection with cytopathic virus were seen. Dendritic cells were not susceptible to the cytopathic effect caused by cp BVDV, whereas monocytes were killed. Analysis of interferon (IFN)-alpha/beta production showed similar levels in monocytes and DCs exposed to cp BVDV, but none was detected in cells exposed to ncp BVDV. We conclude that the prevention of cell death in DCs is not associated with enhanced production of IFN-alpha/beta, as proposed for influenza virus, but is by a distinct mechanism.

Alpha/beta and gamma interferons are induced by infection with noncytopathic bovine viral diarrhea virus in vivo

In contrast to the results of previous in vitro studies, experimental infection of calves with noncytopathic bovine viral diarrhea virus (ncpBVDV) was found to induce strong alpha/beta and gamma interferon responses in gnotobiotic animals. These responses were associated with depressed levels of transforming growth factor beta (TGF-beta) in serum. The results of this study indicate that the immunosuppression caused by ncpBVDV is not associated with low interferon responses or elevated levels of TGF-beta.

Masking of two in vitro immunological assays for Mycobacterium bovis (BCG) in calves acutely infected with non-cytopathic bovine viral diarrhoea virus

Acute infection of calves, previously vaccinated with bacille Calmette-Guerin (BCG), with non-cytopathic viral diarrhoea virus (BVDV) resulted in the temporary suppression of two in vitro assays used to monitor Mycobacterium bovis infection. Lymphocyte proliferation and interferon-gamma production by whole blood cultures containing purified protein derivatives prepared from Mycobacterium avium (PPD-A) and M bovis (PPD-B) were markedly suppressed. The implication is that acute infections of cattle with non-cytopathic BVDV may temporarily compromise diagnostic tests for M. bovis infections and result in a failure to identify cattle with tuberculosis.

Establishment of persistent infection with non-cytopathic bovine viral diarrhoea virus in cattle is associated with a failure to induce type I interferon

The establishment of persistent infections with non-cytopathic bovine virus diarrhoea virus (ncpBVDV) is crucial for the maintenance of BVDV in cattle populations. Also, super-infection of persistently infected individuals with antigenically homologous cytopathic BVDV (cpBVDV) results in fatal mucosal disease. Persistent infection with ncpBVDV is established by infection of the foetus during the first trimester of pregnancy. It has been shown previously that foetal infection with cpBVDV does not result in persistent infection. Infection of cells in vitro has demonstrated that cpBVDV induces type I interferon (IFN), whereas ncpBVDV fails to induce IFN. In this study we demonstrate that foetal challenge with cpBVDV results in IFN production, whereas ncpBVDV does not. These findings strongly suggest that the ability of ncpBVDV to inhibit the induction of type I IFN has evolved to enable the virus to establish persistent infection in the early foetus.