Genetic variation in the response to vaccination.

Vaccines are the most powerful means to prevent and diminish the burden of infectious disease. However, there are limitations to their use: vaccines are not yet available for all infectious diseases (including human immunodeficiency virus and respiratory syncytial virus), they sometimes lack efficacy, the response to vaccination is limited by maternal antibodies in very young infants, and the response to vaccination is variable or may even be absent in some individuals. This review focuses on genetic factors that determine the variable response to vaccination. The highly polymorphic human leukocyte antigen system, which is involved in antigen presentation, has been researched most in this aspect, and clearly affects the response to vaccination. Other, but less polymorphic pathways involved are the Toll-like receptor pathway, which is involved in antigen recognition and stimulation of the immune system, and the cytokine immunoregulatory network. The heritability, or the proportion of total variance that is due to additive genetic factors, appears to be particularly large for vaccine-induced antibody responses in young infants compared with cell-mediated responses and antibody responses in older, immunologically more mature individuals. Both antibody and cell-mediated responses are not only affected by loci within, but also strongly by loci outside the human leukocyte antigen system. Because most genes that are important in influencing immune responses to vaccination are still unknown, clearly more work is required. A better understanding of the factors that determine an effective response to vaccination may lead to the identification of specific genes and pathways as targets for the development of novel more uniformly effective vaccines.

[Effect of genetic polymorphisms on the susceptibility to and course of infectious diseases]. / Invloed van genetische polymorfismen op de gevoeligheid voor en het beloop van infectieziekten.

The highly variable susceptibility to and course of infectious diseases are caused by variable environmental factors and by genetic differences in both the pathogens and the host. The genetic variability of the host is determined mainly by polymorphisms in genes that play a role in processes such as adhesion, specific and non-specific immunity, antigen presentation, and inflammation. These variations are important, for example, in infections with HIV or respiratory syncytial virus. It is important to combine genetic knowledge with knowledge about the functional properties of variant genes. Applications of knowledge about genetic variability can be found in the development of vaccines and therapeutic agents, prognostics, and the treatment of individual patients.

[Vaccination against pneumococci and hepatitis B in the Dutch National Immunisation Programme]. / Pneumokokken- en hepatitis B-vaccinatie in het Rijksvaccinatieprogramma.

All infants in the Netherlands, which are born after March 2006, receive additional vaccinations at the age of 2, 3, 4 and 11 months to protect them against pneumococcal infections. During the same visit to a consultation bureau, the children also receive a combination vaccine against diphtheria, pertussis, tetanus, poliomyelitis and Haemophilus influenzae (DTPa-IPV-Hib). Children of which at least one parent was born in a country where hepatitis B occurs relatively often are also vaccinated in the Netherlands against hepatitis B. This currently pertains to about 15% of all newborns. These children now receive a new combination vaccine in which a hepatitis B component has been added to the DTPa-IPV-Hib components. They will receive this combination vaccine 4 times. This combination vaccine is given during the same visit as the pneumococcal vaccination. Although pneumococcal vaccination may have a somewhat negative effect on the immune response to hepatitis B, it is expected that the new 4-fold vaccination schedule will induce good and long-lasting protection against hepatitis B in the vast majority of the children. About 700 children are born out of mothers infected with hepatitis B each year in the Netherlands. In the new vaccination schedule, they now receive 5 active vaccinations against hepatitis B and are examined serologically on an individual basis in order to detect breakthrough infections. This will also generate greater insight into the efficacy of the different vaccination schemes and intervention programmes to prevent vertical transmission of the virus.

Host genetics of Bordetella pertussis infection in mice: significance of Toll-like receptor 4 in genetic susceptibility and pathobiology.

The susceptibility to and the severity of Bordetella pertussis infections in infants and children varies widely, suggesting that genetic differences between individuals influence the course of infection. We have previously identified three novel loci that influence the severity of whooping cough by using recombinant congenic strains of mice: Bordetella pertussis susceptibility loci 1, 2, and 3 (Bps1, -2, and -3). Because these loci could not account for all genetic differences between mice, we extended our search for additional susceptibility loci. We therefore screened 11 inbred strains of mice for susceptibility to a pertussis infection after intranasal infection. Susceptibility was defined by the number of bacteria in the lungs, being indicative of the effect between the clearance and replication of bacteria. The most resistant (A/J) and the most susceptible (C3H/HeJ) strains were selected for further genetic and phenotypic characterization. The link between bacterial clearance and chromosomal location was investigated with 300 F2 mice, generated by crossing A/J and C3H/HeJ mice. We found a link between the delayed clearance of bacteria from the lung and a large part of chromosome 4 in F2 mice with a maximum log of the odds score of 33.6 at 65.4 Mb, which is the location of Tlr4. C3H/HeJ mice carry a functional mutation in the intracellular domain of Tlr4. This locus accounted for all detectable genetic differences between these strains. Compared to A/J mice, C3H/HeJ mice showed a delayed clearance of bacteria from the lung, a higher relative lung weight, and increased body weight loss. Splenocytes from infected C3H/HeJ mice produced almost no interleukin-1beta (IL-1beta) and tumor necrosis factor alpha (TNF-alpha) upon ex vivo restimulation with B. pertussis compared to A/J mice and also showed a delayed gamma interferon (IFN-gamma) production. TNF-alpha expression in the lungs 3 days after infection was increased fivefold compared to uninfected controls in A/J mice and was not affected in C3H/HeJ mice. In conclusion, Tlr4 is a major host factor explaining the differences in the course of infection between these inbred strains of mice. Functional Tlr4 is essential for an efficient IL-1-beta, TNF-alpha, and IFN-gamma response; efficient clearance of bacteria from the lung; and reduced lung pathology.

Genetic control of Bordetella pertussis infection: identification of susceptibility loci using recombinant congenic strains of mice.

Susceptibility to and severity of Bordetella pertussis infection in infants and children vary widely. The spectrum of clinical symptoms ranges from subclinical infection to mild disease, severe whooping cough, and death. The aims of this study were to examine genetic susceptibilities of mice to B. pertussis and to identify genetic loci in the mouse genome that are involved in susceptibility to B. pertussis infection. For this purpose we screened two sets of recombinant congenic strains (RCS) of mice, HcB and CcS, for differences in the numbers of bacteria in the lung 7 days after inoculation. For both CcS and in HcB mice, a wide range in numbers of bacteria in the lung was found, suggesting that the course of infection is under multigenic control. From both RCS sets of mice, we selected one strain to identify possible susceptibility loci in F(2) hybrid mice. The degree of lung colonization 7 days postinoculation in these F(2) mice was evaluated in relation to genetic markers by linkage analysis. We found three novel loci that are involved in the control of B. pertussis infection. One locus, designated B. pertussis susceptibility locus 1 (Bps-1), was identified on chromosome 12. The presence of the C57BL/10 genome on this locus instead of the C3H genome significantly decreased the number of B. pertussis bacteria in the lung. Bps-1 has a dominant-positive effect on the clearance of B. pertussis from the lung. The function of most genes in this region is unknown. Two other loci, Bps-2 and Bps-3, showed genetic interaction and are located on chromosomes 5 and 11. We aim to identify the gene(s) in these regions which modify susceptibility to B. pertussis.

[Protection of children born to hepatitis-B-infected mothers]. / Bescherming van kinderen geboren uit met hepatitis-B-virus geïnfecteerde moeders.

The vaccination schedule implemented on 1 March 2003 for the approximately 1000 Dutch children per year born to hepatitis-B-virus-infected mothers is under discussion. The Health Council of The Netherlands and TNO have both published reports which reveal that the current schedule does not fulfil its objectives, as too many children are completely missed and many of the vaccinated children do not receive their scheduled vaccinations on time. Furthermore, doubts have been expressed about the effectiveness of the present vaccination schedule. In line with one of the schedules proposed by the Health Council we suggest the introduction of a 4-dose vaccination, in which the first vaccination is given immediately after the birth of the child. The subsequent vaccinations can then take place after 2, 4 and 11 months. These are the ages at which other children are also vaccinated against hepatitis B in accordance with the Dutch national vaccination programme. Furthermore, we advise an improved surveillance to ensure compliance with the individual vaccination schedules for these children. If data from the hepatitis-B screening of pregnant women, the regional vaccination registers, and the vaccinations actually administered are linked, then it will be possible to take swift action if a child is late for a hepatitis-B vaccination. In our opinion, this can best be achieved if a single national organisation is made responsible for the entire process, starting from the collection of the hepatitis-B data of pregnant women up to concluding the scheme, whether or not the serologic response is checked.

Timing of infection and prior immunization with respiratory syncytial virus (RSV) in RSV-enhanced allergic inflammation.

Respiratory syncytial virus (RSV) infection has been shown to be a risk factor for the development of allergy in humans and mice. The allergy-enhancing properties of RSV may be dependent on atopic background and an individual's history of RSV infection. We examined the influence of the timing of infection and prior inoculation with RSV in a mouse model of allergic asthma. Mice were sensitized to and challenged with ovalbumin (OVA) and were inoculated with RSV either before or during the sensitization or challenge period. One group of mice was inoculated with RSV both before sensitization to OVA and during challenge with OVA. Increased pulmonary expression of interleukin (IL)-4, IL-5, and IL-13 mRNA and aggravated alveolitis and hypertrophy of mucus-producing cells were observed only when OVA-sensitized mice were inoculated with RSV shortly before or during challenge with OVA. Despite protection against viral replication, prior inoculation with RSV did not abrogate RSV-enhanced, OVA-induced expression of T helper 2 (Th2) cytokines in the lung. In conclusion, inoculation with RSV enhances allergic disease only when the immune system has already been Th2-primed by the allergen (i.e., OVA). This RSV-enhanced allergy is not completely abrogated by prior inoculation with RSV.

Respiratory syncytial virus, pneumonia virus of mice, and influenza A virus differently affect respiratory allergy in mice.

BACKGROUND: Respiratory viral infections in early childhood may interact with the immune system and modify allergen sensitization and/or allergic manifestations. In mice, respiratory syncytial virus (RSV) infection during allergic provocation aggravates the allergic T helper (Th) 2 immune response, characterized by the production of IL-4, IL-5, and IL-13, and inflammatory infiltrates. However, it is unclear whether the RSV-enhanced respiratory allergic response is a result of non-specific virus-induced damage of the lung, or virus-specific immune responses. OBJECTIVE: In the present study we investigated whether RSV, pneumonia virus of mice (PVM) and influenza A virus similarly affect the allergic response. METHODS: BALB/c mice were sensitized and challenged with ovalbumin (OVA), and inoculated with virus during the challenge period. Pulmonary inflammation, lung cytokine mRNA responses, and IgE production in serum were assessed after the last OVA-challenge. RESULTS: Like RSV, PVM enhanced the OVA-induced pulmonary IL-4, IL-5, and IL-13 mRNA expression, which was associated with enhanced perivascular inflammation. In addition, PVM increased the influx of eosinophils in lung tissue. In contrast, influenza virus decreased the Th2 cytokine mRNA expression in the lungs. However, like PVM, influenza virus enhanced the pulmonary eosinophilic infiltration in OVA-allergic mice. CONCLUSION: The Paramyxoviruses RSV and PVM both are able to enhance the allergic Th2 cytokine response and perivascular inflammation in BALB/c mice, while the Orthomyxovirus influenza A is not.

Pathogenesis of poliovirus infection in PVRTg mice: poliovirus replicates in peritoneal macrophages.

The pathogenesis of poliovirus infection, responsible for the induction of a poliovirus-specific mucosal immune response following intraperitoneal (i.p.) inoculation of virus in mice transgenic for the poliovirus receptor (PVRTg mice), was studied. Following inoculation of poliovirus, replication was determined by increase in virus titre (TCID(50)) and by PCR of poliovirus-specific negative-strand RNA in peritoneal macrophages, mesenteric lymph nodes, Peyer's patches, duodenum, brain, kidney and liver. The presence of poliovirus antigens in several cell types was detected by immunolabelling. It was demonstrated that poliovirus replicated in the peritoneal macrophages of PVRTg mice, since the virus titre in peritoneal cells was increased compared to the titre in the inoculum. Negative-strand RNA was detected in these cells and most of the poliovirus-immunostained cells had the morphology of macrophages and expressed the macrophage-specific markers CD86 and M1/70 on their surface. Furthermore, in peritoneal lavage, poliovirus was also present in CD19(+) B cells, but not in dendritic or T cells. Moreover, poliovirus was detected in macrophage-like cells in the lamina propria of the intestine, but not in epithelial cells. Replication of poliovirus in mesenteric lymph nodes, Peyer's patches and brain was followed by excretion of virus in the faeces. This suggests that the virus is transported due to migration of macrophages from the peritoneal cavity to mesenteric lymph nodes and the lamina propria of Peyer's patches. It is likely that this route is responsible for the induction of virus-specific IgA in the gut.

Vaccine-induced antibody responses as parameters of the influence of endogenous and environmental factors.

In laboratory animals, an adequate way to assess effects of environmental exposures on the immune system is to study effects on antigen-specific immune responses, such as after sensitization to T-cell-dependent antigens. This probably also applies to testing effects in the human population. It has thus been suggested that antibody responses to vaccination might be useful in this context. Vaccination responses may be influenced by a variety of factors other than environmental ones. One factor is the vaccine itself; a second is the vaccination procedure used. In addition, the intrinsic capacity of the recipient to respond to a vaccine, which is determined by sex, genetic factors, and age, is important. Psychological stress, nutrition, and (infectious) diseases are also likely to have an impact. We reviewed the literature on vaccine response. With regard to exogenous factors, there is good evidence that smoking, diet, psychological stress, and certain infectious diseases affect vaccination titers, although it is difficult to determine to what extent. Genetic factors render certain individuals nonresponsive to vaccination. In general, in epidemiologic studies of adverse effects of exposure to agents in the environment in which vaccination titers are used, these additional factors need to be taken into consideration. Provided that these factors are corrected for, a study that shows an association of exposure to a given agent with diminished vaccination responses may indicate suboptimal function of the immune system and clinically relevant diminished immune response. It is quite unlikely that environmental exposures that affect responses to vaccination may in fact abrogate protection to the specific pathogen for which vaccination was performed. Only in those cases where individuals have a poor response to the vaccine may exogenous factors perhaps have a clinically significant influence on resistance to the specific pathogen. An exposure-associated inhibition of a vaccination response may, however, signify a decreased host resistance to pathogens against which no vaccination had been performed.

Antigenic and molecular heterogeneity in recent swine influenza A(H1N1) virus isolates with possible implications for vaccination policy.

In order to explore the occurrence of antigenic drift in swine influenza A(H1N1) viruses and the match between epidemic and vaccine strains, 26 virus isolates from outbreaks of respiratory disease among finishing pigs in the Netherlands in the 1995/1996 season and reference strains from earlier outbreaks were examined using serological and molecular methods. In contrast to swine H3N2 viruses, no significant antigenic drift was observed in swine H1N1 viruses isolated from the late 1980s up to 1996 inclusive. However, a marked antigenic and genetic heterogeneity in haemagglutination inhibition tests and nucleotide sequence analyses was detected among the 26 recent swine H1N1 virus strains. Interestingly, the observed antigenic and molecular variants were not randomly distributed over the farms. This finding indicates independent introductions of different swine H1N1 virus variants at the various farms of the study and points to a marked difference between the epidemiologies of human and swine influenza viruses. The observed heterogeneity may hamper the control of swine influenza by vaccination and indicates that the efficacy of current swine influenza vaccines requires re-evaluation and that the antigenic reactivity of swine influenza viruses should be monitored on a regular basis.

An analysis of a presumed major outbreak of pseudorabies virus in a vaccinated sow herd.

We describe a major outbreak of pseudorabies virus (PRV) in a sow herd in which the sows were vaccinated simultaneously three times a year with a vaccine containing Bartha strain. Also in the associated rearing herd in which the gilts were vaccinated twice an outbreak of PRV occurred. The outbreak was analysed with mathematical models, statistical methods and Monte-Carlo simulation. Under the assumption that the outbreak started with one introduction of virus the reproduction ratio R(ind)--as a measure of transmission of PRV between individuals--in the sow herd was estimated with a Generalized Linear Model to be 1.6. Also under the assumption of one introduction of virus R(ind) in the rearing herd was estimated with a martingale estimator to be 1.7. Both estimates were significantly larger than 1. Mathematical analysis showed that heterogeneity in the sow herd, because of the presence of not-optimally immunized replacement sows could not be the only cause of the observed outbreak in the sow herd. With Monte-Carlo simulations, the duration of an outbreak after a single introduction of virus and R(ind) = 1.6 did not mimic the data and thus the hypothesis of a single introduction with R(ind) = 1.6 could also be rejected and R(ind) is thus, not necessarily above 1. Moreover, with statistical analysis, endemicity in the combination of herds as a cause for the observed outbreak could be rejected. Endemicity in the rearing herd alone could not be excluded. Therefore, multiple introductions from outside and most probably from the rearing herd were possibly the cause of the observed outbreak(s). The implications for eradication of pseudorabies virus were discussed.

Deletion of the UL21 gene in Pseudorabies virus results in the formation of DNA-deprived capsids: an electron microscopy study.

We studied the morphogenesis of three pseudorabies virus mutants lacking parts of the gene homologous to the UL21 gene of the herpes simplex virus type 1. The mutants were examined in an SK-6 cell-line, in an SK-6 cell-line expressing the UL21 gene product, in porcine lung alveolar macrophages (PLAM) and in porcine nasal mucosa explants. Although on SK-6 cells and PLAM, the virus-assembly and egress of mutant virus M155, lacking almost the entire UL21 gene, was similar to that of the rescued PRV mutant, M155 producing virions containing little or no DNA (A-type particles). Virus mutants M133 and M134 (lacking 23 and 232 amino acids respectively) produced more C-type particles. In SK-6 cells stably expressing the UL21-encoded protein, all mutants produced C-type particles. All mutants produced C-type particles in nasal mucosa explants, indicating that the UL21-gene product is not essential for virus production in porcine tissue. These results support and extend previous work that indicated a role for the UL21 encoded protein in the packaging of newly replicated viral DNA.

Immunity to poliomyelitis in The Netherlands.

Despite a vaccination coverage rate of 97%, several poliomyelitis outbreaks occurred in the Netherlands during the last three decades, all among sociogeographically clustered, unvaccinated persons. Therefore, to eradicate polio, insight into poliomyelitis immunity is particularly useful. In 1995-1996, the authors conducted a population-based study and determined neutralizing antibodies against poliovirus types 1, 2, and 3 in 9,274 sera from the general population and from religious groups rejecting vaccination. In the general population, the antibody prevalence (>/=1:8) was 96.6% (95% confidence interval (CI): 95.9, 97.2), 93.4% (95% CI: 92.3, 94.5), and 89.7% (95% CI: 88.3, 91.0) for poliovirus types 1, 2, and 3, respectively. Antibodies persisted for long periods in persons with natural immunity as well as in persons whose immunity was induced by inactivated polio vaccine. In Orthodox Reformed persons, the antibody prevalence of poliovirus types 1, 2, and 3 was 65.0% (95% CI: 57.2, 72.9), 59.0% (95% CI: 40.1, 77.9), and 68.7% (95% CI: 65.2, 72.2), respectively. The recent outbreaks clearly affected the seroprevalence profiles of Orthodox Reformed groups but not the general population. At present, there is an insufficient social and political basis for mandatory vaccination; therefore, global eradication of poliovirus seems to be the only way to protect these Orthodox Reformed persons against future poliomyelitis outbreaks.

Discrimination of different subsets of cytolytic cells in pseudorabies virus-immune and naive pigs.

We previously observed that pseudorabies virus (PRV)-induced, cell-mediated cytolysis in pigs includes killing by natural killer (NK) cells. We also observed that IL-2 stimulation in vitro of naive PBMC expands porcine NK cells. The purpose of this study was to compare the phenotypes of the cytolytic subsets stimulated in vitro by PRV and by IL-2. PBMC were isolated from blood of PRV-immune and naive pigs and stimulated in vitro with PRV or IL-2. After 6 days, the frequency of various lymphocyte subsets in these cultured PBMC was determined by flow cytometry: the cells were separated with a magnet-activated cell sorter and the cytolytic activity of the separated populations was determined. When lymphocytes were separated and analysed with FACScan, the following lymphocyte subsets were discriminated: CD6(+) CD8(bright+) CD4(-) (CTL phenotype), CD6(+) CD8(dull+) CD4(+) (the fraction containing memory T helper cells), CD6(+) CD8(-) CD4(+) (T helper cell phenotype), CD6(-) CD8(dull+) CD4(-) gammadelta-T(+) ( gammadelta-T cell phenotype), CD6(-) CD8(dull+) CD4(-) gammadelta-T(-) (NK phenotype) and CD6(-) CD8(-) CD4(-) gammadelta-T(-) or gammadelta-T(+). Flow cytometry analysis demonstrated that PRV stimulation of immune PBMC resulted in the occurrence of more CD6(+) CD8(+) and CD4(+) CD8(+) and fewer CD6(-) CD8(+) and gammadelta-T(+) CD8(+) lymphocytes than IL-2 stimulation of naive PBMC (P<0.05). It was demonstrated further that killing by PRV-stimulated PBMC was mediated mainly by CD6(+) CD8(+) T lymphocytes. Killing by IL-2-stimulated PBMC was mediated mainly by CD6(-) CD8(+) T lymphocytes. These results demonstrate that both natural killing and killing by classical PRV-specific CTL were detected in PRV-immune pigs, whereas IL-2 stimulation of PBMC isolated from naive pigs mainly induced natural killing.

Mucosal and systemic immunity against poliovirus in mice transgenic for the poliovirus receptor: the poliovirus receptor is necessary for a virus-specific mucosal IgA response.

In view of the planned eradication of poliovirus, the suitability of transgenic mice bearing the human receptor for poliovirus (PVRtg mice) as a nonprimate animal model to study mucosal immunity against poliovirus was investigated. After intraperitoneal (ip) priming followed by ip or oral booster with live poliovirus, PVRtg mice had detectable IgA and IgG responses. The IgA response was restricted to PVRtg mice and could not be induced by oral immunization. After ip priming, PVRtg mice did shed virus in the stool, whereas control mice did not. Moreover, the amount of virus shed in the stools of PVRtg mice that had an IgA response after immunization was significantly lower than that of nonimmunized mice. A virus-specific mucosal IgA response is dependent on expression of the poliovirus receptor and is influenced by the route of immunization and the virus strain. PVRtg mice are a suitable model for the study of poliovirus-specific immunity and protection against poliovirus infection.

Antibody responses to antigenic sites 1 and 3 of serotype 3 poliovirus after vaccination with oral live attenuated or inactivated poliovirus vaccine and after natural exposure.

Three important antigenic sites involved in virus neutralization on polioviruses in mouse experiments have been identified. These sites are located at the surface of the virion and have been designated antigenic sites 1, 2, and 3. In mice, the antibody response to antigenic site 1 of serotype 3 poliovirus is considered to be immunodominant, but little is known about the immunogenicity of these sites in humans. In the present study, we developed inhibition enzyme-linked immunosorbent assays specific for antigenic sites 1 and 3 to measure antibody responses to these sites in fully vaccinated inactivated poliovirus vaccine (IPV) (n = 63) and oral live attenuated poliovirus vaccine (OPV) (n = 63) recipients and in naturally infected persons (n = 25). Similar levels of antibodies to site 1 in IPV and OPV vaccinees were detected. However, significantly more OPV recipients (88.7%) had detectable antibodies to antigenic site 3 (P < 0.01) than did IPV-vaccinated persons (63. 1%). After an IPV booster vaccination, both previously IPV- and OPV-vaccinated persons responded with a significant increase in antibodies to sites 1 and 3 (P < 0.01). We conclude that the immune response to serotype 3 poliovirus in humans consists of both site 1- and site 3-specific antibodies and that these responses can be induced by either OPV or recent IPV vaccination.

Induction of mucosal immunity by inactivated poliovirus vaccine is dependent on previous mucosal contact with live virus.

The inactivated poliovirus vaccine (IPV) is used for protection against poliomyelitis in The Netherlands. It is not clear, however, whether IPV vaccination can lead to priming of the mucosal immune system and the induction of IgA. It has been demonstrated that IPV vaccination is able to induce strong memory IgA responses in the serum of persons who have been naturally exposed to wild-type poliovirus. This has led to the hypothesis that IPV vaccination is able to induce poliovirus-specific IgA at mucosal sites in persons who have been previously primed with live poliovirus at mucosal sites. To test this hypothesis, the kinetics of the IgA response in serum and saliva after IPV vaccination were examined in persons previously vaccinated with oral poliovirus vaccine (OPV) or IPV. ELISA and enzyme-linked immunospot assays were used for the detection of poliovirus-specific IgA responses. In addition, B cell populations were separated on the basis of the expression of mucosal (alpha4beta7 integrin) and peripheral homing receptors (L-selectin). Parenteral IPV vaccination was able to boost systemic and mucosal IgA responses in previously OPV-vaccinated persons only. None of the previously vaccinated IPV recipients responded with the production of IgA in saliva. In agreement with this finding, a large percentage of the poliovirus-specific IgA-producing lymphocytes detected in previous OPV recipients expressed the alpha4beta7 integrin. It is concluded that IPV vaccination alone is insufficient to induce a mucosal IgA response against poliovirus. In mucosally (OPV-) primed individuals, however, booster vaccination with IPV leads to a strong mucosal IgA response.

Vaccination of pigs against pseudorabies virus with plasmid DNA encoding glycoprotein D.

We analysed the ability of a plasmid carrying the gene encoding glycoprotein D (gD) of pseudorabies virus (PRV) to induce humoral and cell-mediated immune responses and assessed the protection provided by PRV-gD DNA vaccination against challenge infection with PRV. Immunization with plasmid PRV-gD induced neutralizing antibodies and lymphocyte proliferative responses both in mice and pigs. Moreover, when challenged with virulent PRV six weeks following the last immunization, PRV-gD DNA vaccinated pigs excreted virus for a significantly shorter period and showed less clinical symptoms than pigs vaccinated with a control plasmid. Thus, in the target animal, DNA vaccination with PRV-gD DNA induces protective immunity against challenge infection.

Antigenic drift in swine influenza H3 haemagglutinins with implications for vaccination policy.

In order to explore the occurrence of antigenic drift in swine influenza A(H3N2) virus, we examined virus strains from outbreaks of respiratory disease among finishing pigs in the Netherlands in 1996 and 1997 and from earlier outbreaks. In contrast to swine H3N2 strains from the 1980s, the recent isolates did not show significant cross-reactivity with human influenza A(H3N2) viruses from 1972-1975 in haemagglutination inhibition tests. These new strains form a separate branch in the phylogenetic trec of the HA1 parts of HA. We conclude that recently there has been considerable antigenic drift within the swine H3N2 viruses in the Netherlands and Belgium and recommend replacement of the A/Port Chalmers/1/73 (H3N2) strain in the current vaccine by a more recent swine H3N2 isolate.