Virus Neutralizing Antibody Titers Research Articles

Oral vaccination of mice with adenoviral vectors is not impaired by preexisting immunity to the vaccine carrier.

Adenovirus vectors with E1 deleted of the human serotype 5 (AdHu5) and the chimpanzee serotype 68 (AdC68) expressing the glycoprotein of the Evelyn Rokiniki Abelseth strain of rabies virus were tested upon oral application for induction of systemic and mucosal transgene product-specific antibody responses in mice. Both vectors induced systemic and mucosal antibodies to rabies virus, including virus-neutralizing antibodies and protection against a severe intracerebral challenge with a mouse-adapted strain of rabies virus. Pre-existing immunity of AdHu5 virus, which dampens induction of transgene product-specific immunity elicited by AdHu5 vectors given systemically did not impair the response induced by oral vaccination. Oral priming-boosting regimens with either heterologous or homologous adenoviral vectors used sequentially increased both mucosal and systemic antibody titers to rabies virus [corrected]

Production and purification of immunogenic virus-like particles formed by the chimeric infectious bursal disease virus structural protein, rVP2H, in insect larvae

This study describes an alternative approach to produce rVP2H protein using insect larvae of the cabbage looper Trichoplusia ni as hosts for the expression of the protein. The chimeric rVP2H protein, having an extra six histidine residues at the C-terminus of the VP2, a structural protein of infectious bursal disease virus (IBDV), is a vaccine candidate for the prevention of infectious bursal disease. The chimeric rVP2H protein was expressed in insect larvae in form of virus-like particles, in which they maintain their native immunogenic properties. The expression level of rVP2H protein in T. ni larvae was estimated to be approximately 0.4 mg/g of larvae or 0.2 mg/larvae. The rVP2H particles have a uniform morphology of dodecahedral structure with a size of 23 nm in diameter, and the particles could be affinity-purified in one step with immobilized metal-ion affinity chromatography (IMAC) from the larvae homogenate. The recovery of rVP2H protein was approximately 55% following IMAC and the protein was obtained with a purity of around 90%. An additional purification step of ammonium sulphate precipitation was added to speed up the process of microfiltration and ultrafiltration of the homogenate prior to IMAC. This step enhanced the final purity of rVP2H protein to 99%, demonstrating that the purification protocol developed herein was a powerful strategy for obtaining highly pure rVP2H protein from insect larvae. The immunogenicity and protective properties of the larvae-derived rVP2H protein were evaluated using a chicken protection assay. When larvae-derived rVP2H protein was intramuscularly injected into specific-pathogen-free chickens (20 μg/bird), high titres of virus-neutralizing antibodies were induced and the chickens were protected from the infection of a very virulent strain of IBDV isolated locally.

Unmutated immunoglobulin M can protect mice from death by influenza virus infection.

To elucidate the role of class switch recombination (CSR) and somatic hypermutation (SHM) in virus infection, we have investigated the influence of the primary and secondary infections of influenza virus on mice deficient of activation-induced cytidine deaminase (AID), which is absolutely required for CSR and SHM. In the primary infection, AID deficiency caused no significant difference in mortality but did cause difference in morbidity. In the secondary infection with a lethal dose of influenza virus, both AID−/− and AID+/− mice survived completely. However, AID−/− mice could not completely block replication of the virus and their body weights decreased severely whereas AID+/− mice showed almost complete prevention from the reinfection. Depletion of CD8+ T cells by administration of an anti-CD8 monoclonal antibody caused slightly severer body weight loss but did not alter the survival rate of AID−/− mice in secondary infection. These results indicate that unmutated immunoglobulin (Ig)M alone is capable of protecting mice from death upon primary and secondary infections. Because the titers of virus-neutralizing antibodies were comparable between AID−/− and AID+/− mice at the time of the secondary infection, a defect of AID−/− mice in protection of morbidity might be due to the absence of either other Ig classes such as IgG, high affinity antibodies with SHM, or both.

Correlation of haemagglutinin-neuraminidase and fusion protein content with protective antibody response after immunisation with inactivated Newcastle disease vaccines

The correlation between the antigen content of inactivated Newcastle disease (ND) oil emulsion–vaccines and the serological response after immunisation was studied. The haemagglutinin-neuraminidase (HN) and fusion (F) proteins of Newcastle disease virus (NDV) were quantified in 33 inactivated oil-adjuvanted ND vaccines using isopropylmyristate (IPM)-extraction and antigen ELISAs. These commercial vaccines differed in NDV–vaccine strain, the method applied to inactivate the vaccine virus, the vaccine valence and the composition of the oil emulsions. Large differences, up to 100-fold, in the antigen quantities present in different vaccines were found. The NDV–HN content and the NDV–F content of the vaccines both highly correlated with the haemagglutination-inhibiting (HI) antibody titres after immunisation. These correlation’s were found over a 10,000-fold range of applied antigen. The antigen content of the oil emulsion–vaccines also highly correlated with virus neutralising antibody titres. The presence of serum HI antibody titres in individual specific pathogens free (SPF)-chickens after immunisation with inactivated ND vaccines was highly indicative for clinical protection against challenge with the virulent NDV-Herts strain. Our results are the first to demonstrate that the protective serological response after immunisation highly correlates with the antigen content of oil-adjuvanted vaccines.

PATHOGENICITY OF A VENEZUELAN EQUINE ENCEPHALOMYELITIS SEROTYPE IE VIRUS ISOLATE FOR PONIES

The enzootic or endemic strains of Venezuelan equine encephalomyelitis (VEE) virus (ID, IE, IF, and II-VI) are considered avirulent. In 1993 and 1996, outbreaks of encephalitis occurred in the horse populations in the Chiapas and Oaxaca provinces of Mexico, respectively. In both instances, enzootic VEE virus subserotype IE was isolated from brain tissues of dead horses. The present study investigated the pathogenicity of the Chiapas viral isolate (NVSL VEE IE 93-42124) in ponies. Three ponies were inoculated intradermally with 4, 5, and 6 logs, respectively, of the NVSL VEE IE 93-42124 viral isolate. All ponies showed fluctuations in body temperature, encephalitis, and other signs of infection with VEE virus. Virus was isolated only from the blood of ponies from day 1 to day 3 postinfection. Microscopic examination of hematoxylin and eosin-stained tissue sections showed mild to moderate nonsuppurative encephalitis, perivascular cuffing by mononuclear cells, gliosis, and meningoencephalitis. Antibody (IgM) to VEE virus IE was unable to differentiate between various subserotypes of VEE I viruses (serotypes IAB, IC, ID, and IF). Virus neutralizing antibody titers to heterologous VEE I viruses were 10-100-fold less than those for NVSL VEE IE 93-42124 virus and Mena II, a human isolate of VEE IE virus. The study confirmed that NVSL VEE IE 93-42124 virus, which was isolated from a brain of a horse during an outbreak of VEE in Chiapas, Mexico, was pathogenic for ponies.

A comparison of DNA vaccines for the rabies-related virus, Mokola

Mokola virus, a rabies-related virus, has been reported to date from the African continent only. Like rabies virus, it is highly pathogenic, causes acute encephalitis, and zoonotic events have been documented. Although believed to be rare, there has been an unexplained increase in the number of isolations of the virus in South Africa in recent years. We have cloned and sequenced the glycoprotein (G) and nucleoprotein (N) genes from a South African Mokola virus, and used these in the construction of different DNA vaccines for immunization against Mokola virus. Four vaccines, utilizing different promoters and DNA backbone compositions, were generated and compared for efficacy in protection against Mokola virus. In one of these, both the Mokola virus G and N genes were co-expressed. Two of the single G-expressing DNA vaccines (based on pSG5 and pCI-neo, respectively) protected laboratory mice against lethal challenge, despite major differences in their promoters. However, neither vaccine was fully protective in a single immunization only. Serological assays confirmed titers of virus-neutralizing antibodies after immunization, which increased upon booster vaccine administration. A third construct (based on pBudCE4) was less effective in inducing a protective immune response, despite employing a strong CMV enhancer/promoter also used in the pCI-neo plasmid. Dual expression of Mokola virus G and N genes in pBudCE4 did not enhance its efficacy, under the conditions described. In addition, no significant utility could be demonstrated for a combined prime-boost approach, as no cross-protective immunity was observed against rabies or Mokola viruses from the use of pSG5-mokG or vaccinia-rabies glycoprotein recombinant virus vaccines, respectively, even though both vaccines provided 60–100% protection against homologous virus challenge.

Raccoon Poxvirus as a Mucosal Vaccine Vector for Domestic Cats

In the present study, we evaluated both the immunogenicity and safety of recombinant raccoon poxvirus (RCN) as a mucosal vaccine vector for domestic cats. RCN is an orthopoxvirus that was isolated from healthy raccoons and has been used experimentally as a vaccine vector for rabies and other antigens in a variety of species, including raccoons, skunks, foxes, bobcats, rabbits, domestic cats, piglets, sheep and non-human primates. We evaluated the antibody response induced by a recombinant RCN vaccine expressing the rabies-G glycoprotein (RCN/rabies-G) administered to cats by the oral (PO), intranasal (IN), conjunctival (CO) or intranasal/conjunctival (IN/CO) route (dose: 108 plaque forming units or PFU). The IN route, either alone or combined with the CO route, induced the highest rabies virus neutralizing antibody (RVNA) titers. The RVNA titers remained high when measured at six months post-vaccination, demonstrating that the recombinant vaccine administered via these routes is very efficient at inducing long-lasting immunity. A dose-response was observed following IN vaccination in cats. Doses of 107 PFU induced strong antibody responses in 4 of 5 animals [geometric mean titer: 3.2 (log10)]. None of the animals vaccinated with 104 PFU developed detectable RVNA titers. In this study, RCN/rabies-G viral shedding was below detectable levels. Nasal, oral and fecal swabs collected from these cats were negative for RCN by both virus isolation and by nested-PCR. In addition, no horizontal transmission of the virus could be detected. Gang-housed sentinel animals for each group did not develop detectable anti-RVNA or -RCN antibodies. To study tissue tropism of recombinant raccoon poxvirus vaccines, a RCN that can express the lacZ gene (RCN/lacZ) was constructed. Expression of β-galactosidase (β-gal) was validated in vitro and in mice in vivo. Cats were vaccinated IN with 107 PFU of RCN/lacZ. No histopathological lesions were detected in any of the tissues collected from these cats at 1, 4, 7 and 15 days post-vaccination. In addition, no virus or β-gal expression was detected in any of these tissues. Controls demonstrated that virus could be reisolated from nasal swabs immediately after administration of 108 PFU to cats. These results suggest that recombinant RCN vaccines undergo limited replication after intranasal administration in cats that is sufficient to elicit strong, long-lasting systemic antibody responses.

Conjunctival macrophage-mediated influence of the local and systemic immune response after corneal herpes simplex virus-1 infection.

Recently it has been shown that selective subconjunctival macrophage depletion reduced the incidence and severity of stromal herpes simplex virus (HSV) keratitis in mice. In this study, we examined the effect of conjunctival macrophage depletion on the corneal and systemic T-cell-mediated immune response. BALB/c mice were treated with subconjunctival injections of dichloromethylene diphosphonate (Cl2MDP)-liposomes (Cl2MDP-LIP) or phosphate-buffered saline (PBS) 7 and 2 days before corneal infection with 105 plaque-forming units (PFU) of HSV-1 (KOS strain). Interferon (IFN)-gamma, interleukin (IL)-2, and IL-4 production in the cornea was analysed by enzyme-linked immunosorbent assay (ELISA), and cytokine mRNA levels (IFN-gamma, IL-4) were measured by semiquantitative reverse transcription-polymerase chain reaction (RT-PCR). Cell culture supernatants from submandibular lymph nodes were analysed by ELISA for expression of IFN-gamma, IL-2, and IL-4 and by bioassay for IL-6. The HSV-1-specific proliferative response of lymphocytes from regional lymph nodes and the delayed-type hypersensitivity (DTH) response were tested after corneal infection. Virus-neutralizing antibody titres and HSV-1-specific immunoglobulin G (IgG)2a/IgG1-ratios were measured. Cytokine mRNA expression (IFN-gamma, IL-4) and secretion (IFN-gamma, IL-2, IL-4) in the corneas were decreased after HSV-1 corneal infection in the macrophage-depleted mice. The secretion of IFN-gamma and IL-2 was decreased in the regional lymph nodes from Cl2MDP-LIP-treated animals (P<0.05). Furthermore, Cl2MDP-LIP-treated mice had decreased HSV-1 specific proliferative responses (P<0.05) and DTH response after corneal HSV-1 infection (P<0.05). The virus-neutralizing serum-antibody levels (P<0.05) increased while the HSV-1 specific IgG2a/IgG1-ratio was unaffected after macrophage depletion. Macrophage depletion did not induce a shift between the T helper 1 (Th1) and Th2 response in this HSK model. The data suggest that conjunctival macrophage functions are enhancing the T-cell-mediated immune response after corneal infection. This effect is at least in part responsible for the impaired course of herpetic keratitis after macrophage depletion.

Effect of the contents and form of rabies glycoprotein on the potency of rabies vaccination in cattle.

One of the methods used for controlling cattle rabies in Brazil consists of vaccination. Sometimes, however, rabies occurs in cattle supposedly protected. Since rabies vaccine batches are officially controlled by tests performed on laboratory animals, it is questionable whether the minimal mandatory requirements really correspond to immunogenicity in the target species. We have analyzed the association among potencies of rabies vaccines tested by the NIH test, the contents and form (free-soluble or virus-attached) of rabies glycoprotein (G) in the vaccine batches, and the virus-neutralizing antibodies (VNA) titers elicited in cattle. No correlation was found between G contents in the vaccine batches and the NIH values, whatever the presentation of G. There was no correlation either between NIH values and VNA titers elicited in cattle. There was, however, a positive correlation (r = 0.8681; p = 0.0001) between the amounts of virion-attached G present in the vaccine batches and VNA elicited in cattle. This was not observed when the same analysis was performed with total-glycoprotein or free-soluble glycoprotein. The study demonstrated that NIH values can not predict the effect of the immunogen in cattle. On the other hand, the quantification of virus-attached rabies glycoprotein has a strong correlation with VNA elicited in cattle.

Temporal effects of gamma interferon deficiency on the course of Friend retrovirus infection in mice.

The current studies demonstrate complex and seemingly contradictory effects by gamma interferon (IFN-gamma) on Friend virus (FV) infection. Both temporal and tissue-specific effects were observed. During the first week of infection, IFN-gamma-deficiency caused increased levels of FV infection in multiple tissues. Surprisingly, however, by 2 weeks postinfection, IFN-gamma-deficient mice had significantly lower levels of infection in both the spleen and bone marrow compared to wild-type mice. The rapid reduction of virus in the IFN-gamma-deficient mice correlated with a more rapid virus-neutralizing antibody response than was observed in the wild-type mice. Furthermore, the virus-neutralizing antibody response in wild-type mice could be accelerated by ablation of their IFN-gamma response. Although the IFN-gamma-deficient mice developed an accelerated virus-neutralizing antibody response, they did not class-switch to immunoglobulin G class immunoglobulins nor could they maintain long-term virus-neutralizing antibody titers. Eventually, all of the IFN-gamma-deficient mice failed to keep persistent virus in check and developed fatal FV-induced erythroleukemia.

Induction of protective immunity by topic application of a recombinant adenovirus expressing rabies virus glycoprotein

The objective of this study was to determine if a replication defective recombinant adenovirus expressing rabies virus glycoprotein (Adrab.gp) given through a non-invasive vaccination route (by topical application) onto the skin (NIVS) could elicit an immune response and/or protection against rabies. Groups of mice were immunized by NIVS with various doses of Adrab.gp. For comparison, groups of mice were immunized intramuscularly, subcutaneously, or intradermally with Adrab.gp. Mice received two booster immunizations at 1 and 2 months after the first immunization. Virus neutralizing antibody (VNA) titers were measured at day 21 after the first and second immunizations and at day 14 after the third immunization. Fifty percent of the mice immunized by NIVS with 2×10 7 and 2×10 8 pfu Adrab.gp vaccine developed VNA, whereas none of the control mice or the mice immunized by NIVS with the lowest dose (2×10 6 pfu) of Adrab.gp virus developed VNA. However, this low dose induced high titers of VNA in mice immunized by parenteral routes. Two weeks after the last immunization, all the mice were challenged with a lethal dose of rabies virus. More than 70% of the animals immunized by NIVS with ≥2×10 7 pfu Adrab.gp virus survived the challenge, whereas all the mice in the negative control group and the group immunized by NIVS with the lowest dose of Adrab.gp succumbed to rabies. Taken together, the results suggest that NIVS with Adrab.gp can induce VNA production and protection against lethal challenge with rabies virus in mice.

Protective efficacy of a plasmid DNA encoding Japanese encephalitis virus envelope protein fused to tissue plasminogen activator signal sequences: studies in a murine intracerebral virus challenge model

We report the construction of chimeric DNA vaccine vectors in which secretory signal sequence derived from tissue plasminogen activator (TPA) was fused to the full length (pCMVTE) or 398 amino terminal amino acids (pCMVTΔE) of Japanese encephalitis virus (JEV) envelope (E) protein. Transfection studies indicate that E protein expressed from pCMVTΔE-transfected cells but not pCMVTE-transfected cells is secreted into the culture medium. Analysis of the potency of various DNA vaccine constructs in a murine intracerebral (i.c.) JEV challenge model indicates that pCMVTΔE confers the highest level (71%) of protection. Immunization with pCMVTΔE induces a mixed Th1 and Th2 T helper cell response while immunization with plasmids encoding nonsecretory forms of E protein induces a Th1 T helper response. Only low levels (<1:20) of virus neutralizing antibody titres were observed in DNA vaccinated mice which did not increase further after i.c. JEV challenge. Thus, immunization with a plasmid encoding secretory E protein results in an altered cytokine response and better protection against i.c. JEV challenge than that conferred by immunization with plasmids encoding nonsecretory forms of E protein. We also demonstrate that unlike peripheral JEV challenge, i.c. JEV challenge does not result in an increase in anamnestic antibody response suggesting that other components of immune system such as cytotoxic T cells and T helper cells contribute to protection against i.c. JEV challenge of DNA vaccinated mice.

Field trial with oral vaccination of dogs against rabies in the Philippines

BackgroundThe potential role of oral vaccination of dogs against rabies in the Philippines was investigated in terms of safety and efficacy.MethodsPrior to the vaccination campaign, a house-to-house survey was carried out to collect data on the dog population in the study area, the coastal village of Mindoro. During the vaccination campaign all households were visited again, and all dogs encountered (>2 months old) were, if possible, vaccinated. Furthermore, 14 dogs vaccinated were bled on different occasions.ResultsDuring the survey, a total of 216 dogs were counted, and none of these animals had previously been vaccinated against rabies. Only 17 dogs could be restrained and subsequently vaccinated directly by the vaccinators. Another 126 dogs were offered a local-made boiled intestine bait, containing a capsule filled with 3.0 ml SAD B19 (107.9 FFU/ml). The bait acceptance rate of dogs offered a bait was 96.1%. The vaccination coverage of the dog population (> 2 months old) estimated by the number of animals vaccinated directly and the number of dogs that accepted a bait and subsequently punctured the vaccine container was 76%. Fifteen and 29 days after the vaccination campaign 6 and 10 dogs (n = 14) had rabies virus neutralizing antibody titres of ≥ 0.5 IU/ml, respectively. No unintentional contacts of nontarget species, including humans, with the vaccine virus were reported.ConclusionsThe results of the campaign show that oral vaccination of dogs against rabies is a promising supplementary method in dog rabies control in the Philippines.

Overexpression of cytochrome C by a recombinant rabies virus attenuates pathogenicity and enhances antiviral immunity.

The pathogenicity of individual rabies virus strains appears to correlate inversely with the extent of apoptotic cell death they induce and with the expression of rabies virus glycoprotein, a major inducer of an antiviral immune response. To determine whether the induction of apoptosis by rabies virus contributes to a decreased pathogenicity by stimulating antiviral immunity, we have analyzed these parameters in tissue cultures and in mice infected with a recombinant rabies virus construct that expresses the proapoptotic protein cytochrome c. The extent of apoptosis was strongly increased in primary neuron cultures infected with the recombinant virus carrying the active cytochrome c gene [SPBN-Cyto c(+)], compared with cells infected with the recombinant virus containing the inactive cytochrome c gene [SPBN-Cyto c(-)]. Mortality in mice infected intranasally with SPBN-Cyto c(+) was substantially lower than in SPBN-Cyto c(-)-infected mice. Furthermore, virus-neutralizing antibody (VNA) titers were significantly higher in mice immunized with SPBN-Cyto c(+) at the same dose. The VNA titers induced by these recombinant viruses paralleled their protective activities against a lethal rabies virus challenge infection, with SPBN-Cyto c(+) revealing an effective dose 20 times lower than that of SPBN-Cyto c(-). The strong increase in immunogenicity, coupled with the marked reduction in pathogenicity, identifies the SPBN-Cyto c(+) construct as a candidate for a live rabies virus vaccine.

Prolonged E55+ retrovirus expression in aged mice is associated with a decline in the anti-virus immune response.

E55+ murine leukemia retrovirus (E55+ MuLV) infection of young and aged C57BL/6 (B6) mice was used to investigate the relationship between increased incidences of infection and decreased immune responsiveness of elderly individuals. Young mice decreased E55+ MuLV burden to below detectable levels by 8 weeks postinfection (p.i.). In contrast, virus burden in aged mice did not reach undetectable levels until 20 weeks p.i. A significant T cell proliferative response to E55+ MuLV was detected from 2 to 12 weeks p.i. in young mice, but was never observed in aged mice. Both age groups demonstrated significant E55+ MuLV-specific T-cell-mediated cytotoxic responses at 3 and 4 weeks p.i. and virus neutralizing antibody titers at 2, 4, 8, and 12 weeks p.i. In both cases, responses were consistently higher in young mice (P < 0.04 and P < 0.02, respectively). These results demonstrate that the observed delay in E55+ MuLV clearance by aged mice is associated with an age-related decrease in the immune response to the virus.

Evaluation of a prototype sub-unit vaccine against equine arteritis virus comprising the entire ectodomain of the virus large envelope glycoprotein (G(L)): induction of virus-neutralizing antibody and assessment of protection in ponies.

An Escherichia coli-expressed recombinant protein (6hisG(L)ecto) comprising the entire ectodomain (aa 18-122) of equine arteritis virus (EAV) glycoprotein G(L), the immunodominant viral antigen, induced higher neutralizing antibody titres than other G(L)-derived polypeptides when compared in an immunization study in ponies. The potential of the recombinant G(L) ectodomain to act as a sub-unit vaccine against EAV was evaluated further in three groups of four ponies vaccinated with doses of 35, 70 or 140 microg of protein. All vaccinated animals developed a virus-neutralizing antibody (VNAb) response with peak titres 1-2 weeks after the administration of a booster on week 5 (VNAb titres of 1.8-3.1), 13 (VNAb titres of 1.4-2.9) or 53 (VNAb titres of 1.2-2.3). Vaccinated and unvaccinated control ponies were infected with EAV at different times post-vaccination to obtain information about the degree of protection relative to the levels of pre-challenge VNAb. Vaccination conferred varying levels of protection, as indicated by reduced or absent pyrexia, viraemia and virus excretion from the nasopharynx. The degree of protection correlated well with the levels of pre-challenge VNAb and, in particular, with levels of virus excretion. These results provide the first evidence that a sub-unit vaccine protects horses against EAV. The use of the sub-unit vaccine in combination with a differential diagnostic test based on other EAV antigens would enable serological discrimination between naturally infected and vaccinated equines.

Analysis of the quality of protection induced by a porcine influenza A vaccine to challenge with an H3N2 virus

Antigenic drift of swine influenza A (H3N2) viruses away from the human A/Port Chalmers/1/73 (H3N2) strain, used in current commercial swine influenza vaccines, has been demonstrated in The Netherlands and Belgium. Therefore, replacement of this human strain by a more recent swine H3N2 isolate has to be considered. In this study, the efficacy of a current commercial swine influenza vaccine to protect pigs against a recent Dutch field strain (A/Sw/Oedenrode/96) was assessed. To evaluate the level of protection induced by the vaccine it was compared with the optimal protection induced by a previous homologous infection. Development of fever, virus excretion, and viral transmission to unchallenged group mates were determined to evaluate protection. The vaccine appeared efficacious in the experiment because it was able to prevent fever and virus transmission to the unchallenged group mates. Nevertheless, the protection conferred by the vaccine was sub-optimal because vaccinated pigs excreted influenza virus for a short period of time after challenge, whereas naturally immune pigs appeared completely protected. The immune response was monitored, to investigate why the vaccine conferred a sub-optimal protection. The haemagglutination inhibiting and virus neutralising antibody responses in sera, the nucleoprotein-specific IgM, IgG, and IgA antibody responses in sera and nasal secretions and the influenza-specific lymphoproliferation responses in the blood were studied. Vaccinated pigs developed the same or higher serum haemagglutination inhibiting, virus neutralising, and nucleoprotein-specific IgG antibody titres as infected pigs but lower nasal IgA titres and lymphoproliferation responses. The lower mucosal and cell-mediated immune responses may explain why protection after vaccination was sub-optimal.

Efficacy of inactivated infectious bursal disease (IBD) vaccines: Comparison of serology with protection of progeny chickens against IBD virus strains of varying virulence

The efficacy of inactivated infectious bursal disease vaccines was determined by measuring both the antibody response of vaccinated chickens and clinical protection of progeny chicks from vaccinated dams. Similar virus neutralizing (VN) antibody titres were obtained in 4-week-old chickens and mature hens after vaccination with one vaccine dose. VN titres below 10 log 2 increased considerably between the fourth and seventh week after vaccination in 4-week-old chickens as well as in mature chickens. All 2-week-old progeny chicks with serum VN antibody titres of at least 9 log 2 were clinically protected against the classical virulent 52/70 infectious bursal disease virus (IBDV) strain, as well as against the very virulent IBDV (vvIBDV) strain D6948. However, vaccination often did not prevent subclinical infection in these 2-week-old progeny chicks, which often resulted in severe lymphocyte depletion in the bursa of Fabricius. Even a serum VN titre of 11 log 2 was not always sufficient to prevent severe bursal damage. Although 52/70 IBDV and vvIBDV were equally pathogenic in 2-weekold specific pathogen free chickens, significant higher maternal antibody titres were required to prevent the adverse effects of vvIBDV in comparison with 52/70 IBDV. The relation between the serological response of chickens after application of inactivated IBD vaccines and the protection of progeny chicks of vaccinated dams depended on both the virulence of the IBDV challenge strain and the IBDV strain in the vaccine.

T-Cell suppression by cyclosporin-A enhances infectious bursal disease virus infection in experimentally infected chickens

In this study, the role of T lymphocytes was investigated in chickens experimentally infected with infectious bursal disease virus (IBDV). Chickens were treated with cyclosporin-A (CS-A), a selective T-cell suppressant drug, by the intramuscular route, starting 3 days before virus infection and every third day thereafter,and infectious bursal disease pathogenesis was compared in such T-cell suppressed and intact chickens using a vaccine strain; namely, Georgia and a field isolate of IBDV. Treatment of chickens with CS-A caused a significant suppression of phytohaemagglutinin-A specific proliferative responses of peripheral blood mononuclear cells. The virus neutralizing antibody titres in such CS-A treated chickens were not suppressed. T-Cell suppression resulted in an increase in the severity of gross lesions caused by IBDV and extensive muscular haemorrhages were observed in such chickens between 15 and 21 days post-inoculation. Similarly, there was a marked increase in the severity of infectious bursal disease-specific microscopic lesions in the bursa of T-cell suppressed chickens. Consistently higher titres of virus were observed in bursa of CS-A treated chickens. Virus titres were 1 to 2 log10 higher in the T-cell suppressed chickens as compared with the intact ones. These studies suggest that T cells play a role in limiting the IBDV infection.

The role of IL-5, IL-6 and IL-10 in primary and vaccine-primed immune responses to infection with Friend retrovirus (Murine leukaemia virus).

The defence of a host against viral infections is strongly influenced by cytokines. We investigated the role of the B-cell stimulating cytokines IL-5 and IL-6, and the immuno-suppressive cytokine IL-10, during primary and secondary immune responses in mice against infection with Friend retrovirus (FV) (Murine leukaemia virus). IL-5(-/-) mice were comparable to C57BL/6 wild-type mice in their ability to control acute FV infection. In contrast, IL-6(-/-) and IL-10(-/-) mice showed significantly enhanced virus loads in spleen cells. However, this impaired control of acute FV replication did not alter the long-term control over persistent FV in IL-6(-/-) and IL-10(-/-) mice. Immunization with a live attenuated vaccine virus prior to challenge protected all three types of cytokine-deficient mice from high levels of spleen virus, despite the finding that the vaccinated IL-5- and IL-6-deficient mice had significantly reduced titres of virus-neutralizing IgG class antibodies. The results indicate that IL-6 and IL-10 contribute to primary immune responses against FV, but are dispensable during persistent infection and vaccine-primed secondary responses.