Efficacy of swine influenza A virus vaccines against an H3N2 virus variant

We compared the efficacy of 3 commercial vaccines against swine influenza A virus (SIV) and an experimental homologous vaccine in young pigs that were subsequently challenged with a variant H3N2 SIV, A/Swine/Colorado/00294/2004, selected from a repository of serologically and genetically characterized H3N2 SIV isolates obtained from recent cases of swine respiratory disease. The experimental vaccine was prepared from the challenge virus. Four groups of 8 pigs each were vaccinated intramuscularly at both 4 and 6 wk of age with commercial or homologous vaccine. Two weeks after the 2nd vaccination, those 32 pigs and 8 nonvaccinated pigs were inoculated with the challenge virus by the deep intranasal route. Another 4 pigs served as nonvaccinated, nonchallenged controls. The serum antibody responses differed markedly between groups. After the 1st vaccination, the recipients of the homologous vaccine had hemagglutination inhibition (HI) titers of 1:640 to 1:2560 against the challenge (homologous) virus. In contrast, even after 2nd vaccination, the commercial-vaccine recipients had low titers or no detectable antibody against the challenge (heterologous) virus. After the 2nd vaccination, all the groups had high titers of antibody to the reference H3N2 virus A/Swine/Texas/4199-2/98. Vaccination reduced clinical signs and lung lesion scores; however, virus was isolated 1 to 5 d after challenge from the nasal swabs of most of the pigs vaccinated with a commercial product but from none of the pigs vaccinated with the experimental product. The efficacy of the commercial vaccines may need to be improved to provide sufficient protection against emerging H3N2 variants.     

Pandemic H1N1 influenza virus in Chilean commercial turkeys with genetic and serologic comparisons to U.S. H1N1 avian influenza vaccine isolates

Beginning in April 2009, a novel H1N1 influenza virus caused acute respiratory disease in humans, first in Mexico and then around the world. The resulting pandemic influenza A H1N1 2009 (pH1N1) virus was isolated in swine in Canada in June 2009 and later in breeder turkeys in Chile, Canada, and the United States. The pH1N1 virus consists of gene segments of avian, human, and swine influenza origin and has the potential for infection in poultry following exposure to infected humans or swine. We examined the clinical events following the initial outbreak of pH1N1 in turkeys and determined the relatedness of the hemagglutinin (HA) gene segments from the pH1N1 to two H1N1 avian influenza (AI) isolates used in commercial turkey inactivated vaccines. Overall, infection of turkey breeder hens with pH1N1 resulted in -50% reduction of egg production over 3-4 weeks. Genetic analysis indicated one H1N1 AI vaccine isolate (Alturkey/North Carolina/17026/1988) contained approximately 92% nucleotide sequence similarity to the pH1N1 virus (A/Mexico/4109/2009); whereas, a more recent AI vaccine isolate (A/ swine/North Carolina/00573/2005) contained 75.9% similarity. Comparison of amino acids found at antigenic sites of the HA protein indicated conserved epitopes at the Sa site; however, major differences were found at the Ca2 site between pH1N1 and A/ turkey/North Carolina/127026/1988. Hemagglutinin-inhibition (HI) tests were conducted with sera produced in vaccinated turkeys in North Carolina to determine if protection would be conferred using U.S. AI vaccine isolates. HI results indicate positive reactivity (HI titer > or = 5 log2) against the vaccine viruses over the course of study. However, limited cross-reactivity to the 2009 pH1N1 virus was observed, with positive titers in a limited number of birds (6 out of 20) beginning only after a third vaccination. Taken together, these results demonstrate that turkeys treated with these vaccines would likely not be protected against pH1N1 and current vaccines used in breeder turkeys in the United States against circulating H1N1 viruses should be updated to ensure adequate protection against field exposure.     

Investigations of the efficacy of European H1N1- and H3N2-based swine influenza vaccines against the novel H1N2 subtype

The efficacy of a commercial swine influenza vaccine based on A/New Jersey/8/76 (H1N1) and A/Port Chalmers/1/73 (H3N2) strains was tested against challenge with an H1N2 swine influenza virus. Influenza virus-seronegative pigs were vaccinated twice with the vaccine when they were four and eight weeks old, or with the same vaccine supplemented with an H1N2 component. Control pigs were left unvaccinated. Three weeks after the second vaccination, all the pigs were challenged intratracheally with the swine influenza strain Sw/Gent/7625/99 (H1N2). The commercial vaccine induced cross-reactive antibodies to H1N2, as detected by the virus neutralisation (VN) assay, but VN antibody titres were 18 times lower than in the pigs vaccinated with the H1N2-supplemented vaccine. The challenge produced severe respiratory signs in nine of 10 unvaccinated control pigs, which developed high H1N2 virus titres in the lungs 24 and 72 hours after the challenge. Vaccination with the commercial vaccine resulted in milder respiratory signs, but H1N2 virus replication was not prevented. Mean virus titres in the pigs vaccinated with the commercial vaccine were 1-5 log10 lower than in the controls at 24 hours but no different at 72 hours. In contrast, the H1N2-supplemented vaccine prevented respiratory disease in most pigs. There was a 4-5 log10 reduction in the mean virus titre at 24 hours in the pigs vaccinated with this vaccine, and no detectable virus replication at 72 hours. These data indicate that the commercial swine influenza vaccine did not confer adequate protection against the H1N2 subtype.     

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.     

Comparison of a commercial enzyme-linked immunosorbent assay with hemagglutination inhibition assay for serodiagnosis of swine influenza virus (H1N1) infection.

A commercial indirect swine influenza virus (SIV) H1N1 enzyme-linked immunosorbent assay (ELISA) was compared with the hemagglutination inhibition (HI) assay by testing 72 samples from experimentally infected pigs and 780 field samples of undefined SIV status. The HI assay was performed using SIV isolates A/Swine/IA/73 for H1N1 and A/Swine/IA/8548-1/98 for H3N2. The ELISA used an SIV isolated in 1988. The results showed that HI and ELISA detected an antibody in 11 and 6, respectively, of 72 serum samples collected from pigs experimentally infected with a 1992 SIV isolate (A/Swine/IA/40776/92). The presence of antibodies in these experimental samples was confirmed by HI tests in which all 72 samples were positive against the homologous virus, a more recent H1N1 SIV isolate (A/Swine/NVSL/01) supplied by National Veterinary Services Laboratories, Ames, Iowa, and a 1999 H1N1 isolate currently used in a commercial vaccine. On testing 780 field samples, an overall agreement of 85.5% was generated between the HI and ELISA. This study demonstrated that the ELISA is a useful serodiagnostic screening test at herd level for detecting swine antibodies against SIV. However, a new SIV isolate representing current SIV strains circulating in the field is needed to replace the older isolates used in the HI and ELISA to increase the test accuracy for serodiagnosis of SIV.     

Influenza A viruses: epidemiologic study in fatteners in Spain (1987-89).

2,979 sera were collected from slaughtered swine in two geographic areas of Spain from 1987 to 1989. They were tested for antibodies against an H1N1- and H3N2-influenza virus by haemagglutination-inhibition tests (HI). The percentage of positive sera was higher in area I (78%-69.2%) than in area II (63.1%-60.4%) for both viruses respectively. The coexistence of high titres to both H1N1- and H3N2-influenza virus became apparent in cold months simultaneously in each area, although influenza viruses circulated in the Spanish swine population for two years. Also this study suggests the possible circulation of A/Texas/1/77-like strains in Spain, results which have not been reported before.     

Evaluation of a protective immunity induced by an inactivated influenza H3N2 vaccine after an intratracheal challenge of pigs.

A challenge study was conducted to evaluate the safety and efficacy of an inactivated influenza H3N2 virus vaccine combined with Quil A/Alhydrogel mixture under controlled conditions in piglets. Twenty-four piglets from 12 sows were allocated to 2 groups; injected intramuscularly with 2 doses of the tested vaccine or with PBS at 2 wk intervals and challenged intratracheally with 105TCID50 of the H3N2 swine influenza virus 6 d after the 2nd immunization. Clinical and virological parameters were recorded for 4 d after the challenge. The use of the tested vaccine produced high serum hemagglutination-inhibition titers against the swine H3N2 strain virus. This strong immune response suppressed all clinical signs and viral shedding and reduced pulmonary lesions due to the challenge in the vaccinated group, without causing any secondary effects. Our results suggest that the serum HI titers correlated with the degree of protection induced by an inactivated swine influenza H3N2 vaccine.     

Serologic surveillance of swine H1 and H3 and avian H5 and H9 influenza A virus infections in swine population in Korea

Influenza A is a respiratory disease common in the swine industry. Three subtypes, H1N1, H1N2 and H3N2 influenza A viruses, are currently co-circulating in swine populations in Korea. An outbreak of the highly pathogenic avian influenza H5N1 virus occurred in domestic bird farms in Korea during the winter season of 2003. Pigs can serve as hosts for avian influenza viruses, enabling passage of the virus to other mammals and recombination of mammalian and avian influenza viruses, which are more readily transmissible to humans. This study reports the current seroprevalence of swine H1 and H3 influenza in swine populations in Korea by hemagglutination inhibition (HI) assay. We also investigated whether avian H5 and H9 influenza transmission occurred in pigs from Korea using both the HI and neutralization (NT) tests. 51.2% (380/742) of serum samples tested were positive against the swine H1 virus and 43.7% (324/742) were positive against the swine H3 virus by HI assay. The incidence of seropositivity against both the swine H1 virus and the swine H3 virus was 25.3% (188/742). On the other hand, none of the samples tested showed seropositivity against either the avian H5 virus or the avian H9 virus by the HI and NT tests. Therefore, we report the high current seroprevalence and co-infectivity of swine H1 and H3 influenza viruses in swine populations and the lack of seroepidemiological evidence of avian H5 and H9 influenza transmission to Korean pigs.     

A novel M2e-multiple antigenic peptide providing heterologous protection in mice

Swine influenza viruses (SwIVs) cause considerable morbidity and mortality in domestic pigs, resulting in a significant economic burden. Moreover, pigs have been considered to be a possible mixing vessel in which novel strains loom. Here, we developed and evaluated a novel M2e-multiple antigenic peptide (M2e-MAP) as a supplemental antigen for inactivated H3N2 vaccine to provide cross-protection against two main subtypes of SwIVs, H1N1 and H3N2. The novel tetra-branched MAP was constructed by fusing four copies of M2e to one copy of foreign T helper cell epitopes. A high-yield reassortant H3N2 virus was generated by plasmid based reverse genetics. The efficacy of the novel H3N2 inactivated vaccines with or without M2e-MAP supplementation was evaluated in a mouse model. M2e-MAP conjugated vaccine induced strong antibody responses in mice. Complete protection against the heterologous swine H1N1 virus was observed in mice vaccinated with M2e-MAP combined vaccine. Moreover, this novel peptide confers protection against lethal challenge of A/Puerto Rico/8/34 (H1N1). Taken together, our results suggest the combined immunization of reassortant inactivated H3N2 vaccine and the novel M2e-MAP provided cross-protection against swine and human viruses and may serve as a promising approach for influenza vaccine development.     

Efficacy of a pandemic (H1N1) 2009 virus vaccine in pigs against the pandemic influenza virus is superior to commercially available swine influenza vaccines

In April 2009 a new influenza A/H1N1 strain, currently named "pandemic (H1N1) influenza 2009" (H1N1v), started the first official pandemic in humans since 1968. Several incursions of this virus in pig herds have also been reported from all over the world. Vaccination of pigs may be an option to reduce exposure of human contacts with infected pigs, thereby preventing cross-species transfer, but also to protect pigs themselves, should this virus cause damage in the pig population. Three swine influenza vaccines, two of them commercially available and one experimental, were therefore tested and compared for their efficacy against an H1N1v challenge. One of the commercial vaccines is based on an American classical H1N1 influenza strain, the other is based on a European avian H1N1 influenza strain. The experimental vaccine is based on reassortant virus NYMC X179A (containing the hemagglutinin (HA) and neuraminidase (NA) genes of A/California/7/2009 (H1N1v) and the internal genes of A/Puerto Rico/8/34 (H1N1)). Excretion of infectious virus was reduced by 0.5-3 log(10) by the commercial vaccines, depending on vaccine and sample type. Both vaccines were able to reduce virus replication especially in the lower respiratory tract, with less pathological lesions in vaccinated and subsequently challenged pigs than in unvaccinated controls. In pigs vaccinated with the experimental vaccine, excretion levels of infectious virus in nasal and oropharyngeal swabs, were at or below 1 log(10)TCID(50) per swab and lasted for only 1 or 2 days. An inactivated vaccine containing the HA and NA of an H1N1v is able to protect pigs from an infection with H1N1v, whereas swine influenza vaccines that are currently available are of limited efficaciousness. Whether vaccination of pigs against H1N1v will become opportune remains to be seen and will depend on future evolution of this strain in the pig population. Close monitoring of the pig population, focussing on presence and evolution of influenza strains on a cross-border level would therefore be advisable.     

Effect of intratracheal challenge of fattening pigs previously immunised with an inactivated influenza H1N1 vaccine

Intratracheal inoculation of a field isolate of influenza A H1N1 caused high fever, anorexia and dyspnoea in unvaccinated pigs. In a limited study, it was shown that animals vaccinated once with an inactivated influenza A H1N1 strain showed partial protection at challenge, indicated by mild or absent clinical signs and by the suppression of viral replication. There appeared to be a correlation between the hemagglutination-inhibition titers of the serum of vaccinated pigs and the degree of protection. Animals vaccinated with two spaced injections were completely protected at challenge. Viral replication was inhibited in their respiratory tract since no virus was isolated from animals at slaughter and no increase in antibody titer was observed in challenged vaccinates followed serologically. It was concluded that vaccination of swine against influenza with an inactivated vaccine can result in a protective immunity in the respiratory tract. The New Jersey vaccine strain could protect against swine influenza strains (H1N1) currently prevalent in several European countries.     

Serological Evidence of Pandemic H1N1 Influenza Virus Infections in Greek Swine

The introduction of the 2009 pandemic H1N1 (pH1N1) influenza virus in pigs changed the epidemiology of influenza A viruses (IAVs) in swine in Europe and the rest of the world. Previously, three IAV subtypes were found in the European pig population: an avian‐like H1N1 and two reassortant H1N2 and H3N2 viruses with human‐origin haemagglutinin (HA) and neuraminidase proteins and internal genes of avian decent. These viruses pose antigenically distinct HAs, which allow the retrospective diagnosis of infection in serological investigations. However, cross‐reactions between the HA of pH1N1 and the HAs of the other circulating H1 IAVs complicate serological diagnosis. The prevalence of IAVs in Greek swine has been poorly investigated. In this study, we examined and compared haemagglutination inhibition (HI) antibody titres against previously established IAVs and pH1N1 in 908 swine sera from 88 herds, collected before and after the 2009 pandemic. While we confirmed the historic presence of the three IAVs established in European swine, we also found that 4% of the pig sera examined after 2009 had HI antibodies only against the pH1N1 virus. Our results indicate that pH1N1 is circulating in Greek pigs and stress out the importance of a vigorous virological surveillance programme.     

Overcoming maternal antibody interference by vaccination with human adenovirus 5 recombinant viruses expressing the hemagglutinin and the nucleoprotein of swine influenza virus

Sows and gilts lack immunity to human adenovirus 5 (Ad-5) vectored vaccines so immunogens of swine pathogens can be expressed with these vaccines in order to immunize suckling piglets that have interfering, maternally derived antibodies. In this study 7-day-old piglets, that had suckled H3N2 infected gilts, were sham-inoculated with a non-expressing Ad-5 vector or given a primary vaccination with replication-defective Ad-5 viruses expressed the H3 hemagglutinin and the nucleoprotein of swine influenza virus (SIV) subtype H3N2. The hemagglutination inhibition (HI) titer of the sham-inoculated group (n = 12) showed continued antibody decay whereas piglets vaccinated with Ad-5 SIV (n = 23) developed an active immune response by the second week post-vaccination. At 4 weeks-of-age when the HI titer of the sham-inoculated group had decayed to 45, the sham-inoculated group and half of the Ad-5 SIV vaccinated pigs were boosted with a commercial inactivated SIV vaccine. The boosted pigs that had been primed in the presence of maternal interfering antibodies had a strong anamnestic response while sham-inoculated pigs did not respond to the commercial vaccine. Two weeks after the booster vaccination the pigs were challenged with a non-homologous H3N2 virulent SIV. The efficacy of the vaccination protocol was demonstrated by abrogation of clinical signs, by clearance of challenge virus from pulmonary lavage fluids, by markedly reduced virus shedding in nasal secretions, and by the absence of moderate or severe SIV-induced lung lesions. These recombinant Ad-5 SIV vaccines are useful for priming the immune system to override the effects of maternally derived antibodies which interfere with conventional SIV vaccines.     

不同鸡新城疫疫苗免疫鸡血清HI抗体的测定

将试验鸡分成3个试验组和1个对照组。A组鸡接种鸡新城疫系疫苗,B组鸡接种油乳剂灭活苗,C组鸡接种鸡新城疫系疫苗,并在接种疫苗后第3、4、5、6、7、9、11、13、15、20、25d采取各组鸡血并分离血清,检测HI抗体。结果表明,接种系疫苗的组,HI抗体效价均值从4.67log2上升到10log2,接种后第5d开始上升,接种后第11d达到峰值,持续6d保持高滴度抗体水平。接种系疫苗的组,HI抗体效价均值从4.67log2上升到7log2,接种后第4d开始上升,接种后第9d达到峰值。接种油乳剂灭活苗的组,HI抗体效价均值从4.67log2上升到9.33log2,接种后第5d开始上升,接种后第11d达到峰值,持续16d保持高滴度抗体水平。系疫苗HI抗体效价上升快,效价高,较适合于紧急接种,油乳剂灭活苗HI抗体效价可在高水平维持较长时间,较适合于预防接种。     

Comparison of humoral and cellular immune responses to inactivated swine influenza virus vaccine in weaned pigs

Humoral and cellular immune responses to inactivated swine influenza virus (SIV) vaccine were evaluated and compared. Fifty 3-week-old weaned pigs were randomly divided into the non-vaccinated control group and vaccinated group containing 25 pigs each. Pigs were vaccinated intramuscularly twice with adjuvanted UV-inactivated A/SW/MN/02011/08 (MN/08) H1N2 SIV vaccine at 6 and 9 weeks of age. Whole blood samples for multi-parameter flow cytometry (MP-FCM) and serum samples for hemagglutination inhibition (HI) assay were collected at 23 and 28 days after the second vaccination, respectively. A standard HI assay and MP-FCM were performed against UV-inactivated homologous MN/08 and heterologous pandemic A/CA/04/2009 (CA/09) H1N1 viruses. While the HI assay detected humoral responses only to the MN/08 virus, the MP-FCM detected strong cellular responses against the MN/08 virus and significant heterologous responses to the CA/09 virus, especially in the CD4+CD8+ T cell subset. The cellular heterologous responses to UV-inactivated virus by MP-FCM suggested that the assay was sensitive and potentially detected a wider range of antigens than what was detected by the HI assay. Overall, the adjuvanted UV-inactivated A/SW/MN/02011/08 H1N2 SIV vaccine stimulated both humoral and cellular immune responses including the CD4-CD8+ T cell subset.     

Consequence of Cryptosporidiosis on the immune response of vaccinated broiler chickens against Newcastle disease and/or avian influenza

The consequence of cryptosporidiosis on the immune response of vaccinated chickens against Newcastle disease and/or avian influenza was studied by using 240, 1 day old, male, white Hy-Line chicks and divided into 8 groups and subgroups. Each group or subgroup was consisting of 30 chicks (15?×?2 replicates). The first and second groups were kept as unvaccinated control, G1uninfected and G2 infected. G3, G4 and G5 contained 2 subgroups A&B (G3A, G3B, G4A, G4B, G5A and G5B). Chicks of subgroup A were vaccinated only while chicks of subgroup B were infected and vaccinated. These chicks were orally inoculated with 5?×?10⁵ oocysts of Cryptosporidium baileyi (C. baileyi) at 2 days of age. Chickens were vaccinated intraocular with live Newcastle disease (ND) vaccine (Hitchner on day 7th and LaSota on day 17th of chicken life) (G3) or vaccinated by subcutaneous route with Volvac®- H5N2- AI vaccine on day 10 of chicken life (G4). Last group (G5) was infected similarly and vaccinated with ND and AI vaccines with the same day, dose and route of vaccination for each one. Random blood samples were collected for 3 weeks post-vaccination for investigation of humoral immune response against Newcastle and/or avian influenza vaccines by the haemagglutination inhibition (HI) test. The results showed that H5N2 vaccine at day 10 of chicken life is effective in chickens indicated by the geometric mean of HI titer against AI virus. The findings of this study showed that the infection with Cryptosporidia in the broiler chicken has a depressive effect on the immune status of the birds vaccinated against ND and/or AI vaccination. Moreover, the obtained protection rates against challenge with virulent ND virus observed to be parallel to the results of HI- test. Also, by using 2 different antigens (one commercial and field prepared antigen) to avian influenza virus, lower Geometric mean (GM) HI titer were appeared in infected and vaccinated group than vaccinated group only. A study of the relative lymphoid organs weight such as bursa of Fabricius from the experimental chicks indicated that those organs were comparable between the groups infected-vaccinated and vaccinated only. Non significant variations in final live weight between uninfected control and infected groups were indicated. Also, H5N2-AI vaccination at 10 days old did not affect the final live weight. ND and/or AI Vaccination could not be a substitute to application of good hygienic measures and fecal examination of the birds especially for protozoal diseases such as cryptosporidiosis. It could be concluded that cryptosporidiosis could be one cause of ND and/or AI vaccination failure in poultry farms.     

Antibody responses induced by Japanese whole inactivated vaccines against equine influenza virus (H3N8) belonging to Florida sublineage clade2

In 2010, the World Organisation for Animal Health recommended the inclusion of a Florida sublineage clade2 strain of equine influenza virus (H3N8), which is represented by A/equine/Richmond/1/07 (Richmond07), in equine influenza vaccines. Here, we evaluate the antigenic differences between Japanese vaccine strains and Richmond07 by performing hemagglutination inhibition (HI) assays. Ferret antiserum raised to A/equine/La Plata/93 (La Plata93), which is a Japanese vaccine strain, reacted with Richmond07 at a similar titer to La Plata93. Moreover, two hundred racehorses exhibited similar geometric mean HI antibody titers against La Plata93 and Richmond07 (73.1 and 80.8, respectively). Therefore, we can expect the antibody induced by the current Japanese vaccines to provide some protection against Richmond07-like viruses.     

Prime-boost immunization with HA/C3d DNA followed by a recombinant pseudorabies virus boost enhanced protective immunity against H3N2 swine influenza virus in mice

DNA and recombinant virus vaccines against swine influenza virus (SIV) have been pursued with promising results, but induce poor immunogenicity. This study evaluated the effects of a vaccine regimen in mice including priming with three DNA vaccines expressing soluble HA (sHA), complete HA (tmHA), or sHA fused with three copies murine C3d (sHA-mC3d3) and boosting with recombinant pseudorabies virus expressing HA (rPRV-HA). Immune responses were monitored by ELISA, HI assays, and virus neutralization. Protective efficacy was evaluated by virus isolation from lungs, distribution in tissues, and pathology following challenge with H3N2 SIV. Priming with sHA-mC3d3 and boosting with rPRV-HA induced higher levels of HA-specific antibodies and yielded the most effective protection. This finding implied that priming with a DNA vaccine expressing C3d fused with antigen and boosting with a recombinant vector vaccine is an effective way to induce protective humoral immunity and prevent some infectious diseases.     

Cell mediated and humoral immune response of chickens to inactivated oil-emulsion infectious bronchitis vaccine

A lymphocyte transformation microassay was used to study cell mediated immunity (CMI) in chickens following primary and secondary vaccination with inactivated oil emulsion infectious bronchitis (IB) vaccine and subsequent challenge with Massachusetts-41 (M-41). Humoral immunity was monitored for comparison, using the haemagglutination inhibition (HI) microassay. Positive stimulation indices (2 to 2.7 after primary and 2 to 4.8 after secondary vaccination) were lower and HI titres were higher than those previously reported following primary and secondary vaccination with live IB vaccines. The highest HI titres appeared in birds which had received the inactivated vaccine as a secondary vaccination. Challenge of vaccinated and revaccinated birds resulted in strong HI and weak CMI secondary responses. There was no correlation between CMI and HI antibody production. Monitoring egg production and clinical signs showed that a high level of protection against challenge resulted from revaccination with an inactivated oil adjuvant vaccine.     

Fusion of C3d with hemagglutinin enhances protective immunity against swine influenza virus

H1N1 and H3N2 are the dominant subtypes causing swine influenza in China and other countries. It is important to develop effective vaccines against both H1N1 and H3N2 subtypes of swine influenza virus (SIV). We examined the effects of a DNA vaccine expressing an influenza HA fused to three copies of murine complement C3d in mice. Plasmids encoding soluble HA (sHA), complete HA (tmHA), or a soluble fused form of HA (sHA-mC3d3) were constructed from the H3N2 subtype of SIV. The immune response was monitored by an enzyme-linked immunosorbent assay (ELISA), hemagglutination inhibition (HI) assays, and virus neutralization tests. Analysis of antibody titers indicated that immunization with HA-mC3d3 resulted in higher titers of anti-HA antibodies and higher antibody affinities, compared with serum from mice immunized with sHA or tmHA. Furthermore, the C3d fusion increased the Th2-biased immune response, by inducing IL-4 production. Splenocytes from mice immunized with sHA-mC3d3 produced about three-fold more IL-4 than did splenocytes from mice immunized with sHA or tmHA. Seven days post-challenge with homologous virus (H3N2), no virus was isolated from the mice immunized with HA-expressing plasmids. However, 10 days post-challenge with heterologous virus (H1N1), only mice immunized with sHA-mC3d3 had no virus or microscopic lesions in the kidneys and cerebrum. In conclusion, C3d enhanced antibody responses to hemagglutinin and protective immunity against SIV of different subtypes.