Immunity to poliovirus after infection and vaccination

Abstract

The aim of this thesis was defined as the study of the contribution of IPV vaccination to the induction of a) protection against poliovirus infection and b) mucosal immunity.We have described the development of new immunological tools for the rapid detection of poliovirus-specific antibodies and have investigated the induction of mucosal immunity after IPV vaccination. Our studies compared the immunity induced by IPV vaccination to the immune responses after OPV vaccination and/or exposure to wild-type poliovirus. The presence of antibodies that protect individuals from poliomyelitis is usually determined by a neutralisation assay using cell cultures. Cell culture assays, however, are technically demanding. Disadvantages of the serum neutralisation test (NT) include its long duration and the need for a manual screening of the test results, making this assay labour intensive, difficult to standardise and less suitable for the screening of large populations. Other assays able to detect poliovirus-specific antibodies have been developed within the last decade [6,7]. However, the new assays estimating immunity to polioviruses measure both neutralising and non-neutralising antibodies, whereas it is the presence of neutralising antibodies that is correlated with protection from (re)infection. A newly developed inhibition ELISA known as the PoBI test (Chapter 2) can replace the NT for the determination of protective levels of antibodies to polioviruses in large-scale population studies. Correlations between the PoBI test and the NT were high: 0.89, 0.89 and 0.84 for serotypes 1, 2 and 3 respectively. The sensitivity of the inhibition ELISA was 98.6%, 97.4% and 92.1% for serotypes 1, 2 and 3 respectively. The specificity of the PoBI test as determined with sera from non-vaccinated persons was also high for all three serotypes (99.0%, 95.8% and 100% for serotypes 1, 2 and 3 respectively). One of the major advantages of the PoBI test over the NT is the use of inactivated virus as the antigen. In view of the ongoing eradication of poliovirus, the use of live poliovirus in diagnostic assays should be discouraged and must cease altogether in the near future. Under these circumstances, the PoBI assay is an excellent replacement for the standard NT. Three important antigenic sites (epitopes) involved in virus neutralisation have been identified on polioviruses in mouse experiments [13]. It has been reported that trypsin, present in the intestinal fluids, can cleave serotype 3 polioviruses at antigenic site 1 [14]. Trypsin cleavage of poliovirus results in drastically altered antigenic properties, and trypsin-cleaved viruses may escape neutralisation by monoclonal antibodies to antigenic site 1 [9]. Antibody responses to antigenic sites 1 and 3 were determined in fully IPV- or OPV-vaccinated recipients and in individuals who had been naturally infected (Chapter 3) in order to study the immunogenicity of these sites in humans and the effect of trypsin exposure in vivo. Both sites were immunogenic in naturally infected humans. No significant differences were detected in the responses to antigenic site 1 between IPV-and OPV-recipients. However, significantly more OPV recipients (88.7%) had detectable antibodies to antigenic site 3 (p<0.01) when compared to IPV-vaccinated persons (63.1%). While there are no major differences in the systemic humoral immune response between IPV- and OPV-vaccinated persons, it is not clear whether parenteral vaccination with IPV can lead to priming of the mucosal immune system. We?Summary 122 developed and evaluated ELISAs for the detection of poliovirus serotype-specific IgA and secretory IgA antibodies, and used these assays to examine IgA responses after wild-type infection or vaccination (described in Chapter 4). All of the examined poliomyelitis patients developed a humoral poliovirus-specific IgA response after infection with wild-type poliovirus. In addition, poliovirus-specific IgA was found more frequently in OPV-vaccinated persons than in IPV-vaccinated persons. We observed an age-related increase in the seroprevalence of IgA in the IPV-vaccinated population of The Netherlands. These results may be explained by the assumption that IgA is induced by infection with live poliovirus (wild-type or OPV strains) in the older population, and is unrelated to the IPV vaccination schedule. This is best illustrated by the finding that children between the ages of 13 and 15, born prior to the serotype 1 outbreak of 1978, had significantly more serotype 1-specific IgA in their serum than serotype 2- or 3-specific IgA. We also found that parenteral vaccination with IPV was able to boost IgA responses in 74% to 87% of a naturally exposed population. While the presence of IgA in IPV-recipients has been previously documented, our findings support the hypothesis that mucosal priming with live virus is necessary to obtain an IgA response after IPV booster vaccination. A group of fully OPV- or IPV-vaccinated recipients were given a booster vaccination with IPV to investigate the effect of IPV vaccination on the mucosal IgA response (described in Chapter 5). ELISA and ELISPOT-assays were used for the detection of poliovirus-specific IgA responses. No induction of poliovirus-specific IgA was detected in either saliva or stool samples from individuals in the IPV-vaccinated group, and no IgA-producing cells could be detected in their blood. These findings led to the conclusion that IPV vaccination is unable to induce a response to poliovirus at the mucosal level, indicating the possibility of a lower level of protection against (re)infection in IPV recipients. However, IPV did induce high levels of circulating IgA in fully OPV-vaccinated subjects at both the humoral and the mucosal level. When B cell populations were separated on the basis of the expression of mucosal (a4b7 integrin) or peripheral (L-selectin) homing receptors, a large percentage (77.3%) of the poliovirus-specific IgA-producing cells in the previously OPV-vaccinated group expressed the a4b7 integrin. It was concluded that IPV vaccination alone is insufficient to induce a mucosal IgA response against poliovirus. Our results did indicate, however, that IPV vaccination can serve as an excellent stimulator of mucosal immunity in mucosally (OPV) primed individuals. These observations indicate that the interpretation of findings from challenge studies using IPV recipients must take into account subjects’ possible previous contact with live poliovirus. Subjects from endemic regions, for example, may have had previous exposure to live poliovirus, and this may explain the reported induction of mucosal IgA by IPV vaccination in the past [2,5,8,10,16,17,19]. Cases of poliomyelitis in which paralysis occurs are very difficult to distinguish clinically from other cases of acute flaccid paralysis (AFP). Several new diagnostic methods have been developed in recent years (in our laboratory and elsewhere) that have not been evaluated under field conditions [3,4,10,11,15,18]. While the virological investigation of stool samples is important, it is a laborious procedure [1]. The detection of poliovirus serotype specific-IgM in AFP patients facilitates the laboratory diagnosis of poliomyelitis and helps to exclude poliovirus as the causative agent (Chapter 6). In fact, virus-specific IgM was detected in the blood for six weeks longer than virus was able to be isolated from stool samples. Poliovirus-specific IgA?Summary 123 persisted in many patients for more than eight weeks after infection and may therefore reflect past exposure rather than a recently acquired infection. For this reason, poliovirus-specific IgA is less suitable for the diagnosis of recent infections. Reports of AFP cases in The Netherlands often succumb to serious delays. As a result, AFP surveillance (in its present form) is not an adequate tool with which to document the absence of poliovirus. To make matters worse, only 18.6% of reported AFP cases are virologically examined in The Netherlands (according to WHO guidelines [1,12]). This implies that poliovirus infection can not be excluded with certainty in 69% of these cases. The IgM ELISA will be helpful in resolving cases of AFP that cannot be retrospectively classified as poliomyelitis and for which serum samples are available. Despite all of the problems discussed above, we are well on our way to the world-wide eradication of poliovirus through the use of the currently available IPV and OPV vaccines. Before vaccination stops, however, we must ensure that all (silent) circulation of poliovirus within vaccine recipients is terminated. Poliovirus infections in vaccinated recipients are hard to detect, since none of these people will develop any clinical signs. It is for this reason that the absence of clinical cases induced by poliovirus in a vaccinated population can never serve as compelling evidence of poliovirus eradication. More sensitive tools must be developed to ensure that poliovirus transmission is halted in the vaccinated population. We were able to detect poliovirus-specific IgA in young IPV-vaccinated children, indicating that they have never been in contact with live poliovirus. This is a clear indication that we are on the right track towards the elimination of poliovirus from The Netherlands. We are only a short time away from a complete absence of poliomyelitis outbreaks.?Summary 124 References 1. Conyn-van Spaendonck MAE, Geubbels ELPE, Suijkerbuijk AWM. Paediatric surveillance of acute flaccid paralysis in The Netherlands in 1995 and 1996. RIVM report nr 213676006, Bilthoven, The Netherlands, 1998. 2. Dick GWA, Dane DS, McAlister J, Briggs M, Nelson R, Fields CMB. Vaccination against poliomyelitis with live virus vaccines; effect of previous Salk vaccination on virus excretion. Brit Med J 1961;2:266-269. 3. Faden H, Modlin JF, Thoms ML, McBean AM, Ferdon MB, Ogra PL. Comparative evaluation of immunization with live attenuated and enhanced-potency inactivated trivalent poliovirus vaccines in childhood: systemic and local immune responses. J Infect Dis 1990;162:1291-1297. 4. Gary HE, Freeman C, Penaranda S, Maher K, Anderson L, Pallansch MA. Comparison of a monoclonal antibody-based IgM capture ELISA with a neutralization assay for assessing response to trivalent oral poliovirus vaccine. J Infect Dis 1997;175:S264-S267. 5. Gelezen WP, Lamb J, Belden EA, Chin TDY. Quantitative relationship of pre-existing homotypic antibodies to the excretion of attenuated poliovirus type 1. Amer J Epidemiology 1966;83:224-237. 6. Gershy-Damet GM, Koffi KJ. Utilization of an ELISA technique for the quantitation of antipoliovirus antibodies in human sera. Bull Soc Pathol Exot Filiales 1987;80:289-294. 7. Hagenaars AM, van Delft RW, Nagel J, van Steenis G, van Wezel AL. A modified ELISA technique for titration of antibodies to poliovirus as an alternative to a virus neutralization test. J Virol Methods 1983;6:233-239. 8. Henry JL, Jaikaran ES, Davies JR, Tomlinson AJH, Mason PJ, Barnes JM, Beale AJ. A study of poliovaccinated in infancy: excretion following challenge with live virus by children given killed or living poliovaccine. J Hyg 1966;64:104-120. 9. Icenogle JP, Minor PD, Ferguson M, Hogle JM. Modulation of humoral responses to a 12- amino acid site on the poliovirus. J Virol 1986;60:297-301. 10. Nishio O, Sumi J, Sakae K, Ishihara Y, Isomura S, Inouye S. Fecal IgA antibody responses after oral poliovirus vaccination in infants and elder children. Microbiol Immunol 1990;34:683-9. 11. Onorato IM, Modlin JF, McBean AM, Thoms ML, Losonsky GA, Bernier RH. Mucosal immunity induced by enhance-potency inactivated and oral polio vaccines. J Infect Dis 1991;163:1-6. 12. Oostvogel PM, Conyn-van Spaendonck MAE, Hirasing RA, van Loon AM. Surveillance of Acute flaccid paralysis in The Netherlands 1992-1994. RIVM report nr. 213676006, Bilthoven, The Netherlands, 1996. 13. Patel V, Ferguson M, Minor PD. Antigenic sites on type 2 poliovirus. Virology 1993;192:361- 364. 14. Roivainen M, Hovi T. Intestinal trypsin can significantly modify antigenic properties of polioviruses: implications for the use of inactivated poliovirus vaccine. J Virol 1987;61:3749- 3753. 15. Roivainen M, Agboatwalla M, Stenvik M, Rysa T, Akram DS, Hovi T. Intrathecal immune response and virus-specific immunoglobulin M antibodies in laboratory diagnosis of acute poliomyelitis. J Clin Microbiol 1993;31:2427-2432. 16. Sabin AB. Present position of immunization against poliomyelitis with live virus vaccines. Brit Med J 1959;1:663-680. 17. Smith JWG, Lee JA, Morris CA, Parker DA, Yetts R, Magreth DI, Perkins FT. The responses to oral poliovaccine in persons aged 16-18 years. J Hyg 1976;76:235-247. 18. Zaman S, Carlsson B, Jalil F, Jeansson S, Mellander L, Hanson LA. Comparison of serum and salivary antibodies in children vaccinated with oral live or parenteral inactivated poliovirus vaccines of different antigen concentrations. Acta Paediatric Scand 1991;80:1166-1173.?Summary 125 19. Zhaori G, Sun M, Ogra PL. Characteristics of the immune response to poliovirus virion polypeptides after immunization with live or inactivated polio vaccines. J Infect Dis 1988;158:160- 165.?