The biological relevance of virus neutralisation sites for virulence and vaccine protection in the guinea pig model of foot-and-mouth disease.

Five neutralisation epitopes have been defined for the O1 Kaufbeuren strain of foot-and-mouth disease virus (FMDV) by neutralising murine monoclonal antibodies (Mabs). A mutant virus which is resistant to all these Mabs also resists neutralisation by bovine polyclonal sera, and this characteristic was exploited in the current study to investigate the biological relevance of neutralisation sites in FMDV virulence and vaccine protection. The five site neutralisation-resistant mutant was shown to be as pathogenic as wild-type virus in the guinea pig model of FMD. Guinea pigs were protected in cross-challenge studies from virulent wild-type and mutant viruses using either wild-type or mutant 146S antigen as inactivated whole virus vaccine. Furthermore, hyperimmune sera raised to either wild-type or mutant antigen offered passive protection against wild-type challenge, in spite of the serum raised against the mutant antigen having minimal neutralising activity in vitro. These results imply that virus neutralisation, at least as defined by the in vitro assay, may not play an essential role in the mechanism of immunity induced by whole inactivated FMDV vaccines.

4-Guanidino-Neu5Ac2en fails to protect chickens from infection with highly pathogenic avian influenza virus.

The effectiveness of the novel sialidase inhibitor 4-guanidino-Neu5Ac2en, which is highly effective in mouse and ferret models of influenza virus infection (von Itzstein et al. (1993) Nature 363, 418-423), has been assessed as a prophylactic agent in the prevention of infection of chickens with highly pathogenic avian influenza viruses. At best a small delay in the onset of pyrexia and death was observed with one strain of fowl plague virus, but not with two other strains. These results demonstrate that a locally acting drug may be ineffective if virus can escape from the site of inoculation and replicate elsewhere.

Chimeric polioviruses that include sequences derived from two independent antigenic sites of foot-and-mouth disease virus (FMDV) induce neutralizing antibodies against FMDV in guinea pigs.

Five poliovirus recombinants containing sequences corresponding to foot-and-mouth disease virus (FMDV) antigenic sites were constructed. Viable virus was recovered from four of these plasmids, in which the VP1 beta B-beta C loop (antigenic site 1) of poliovirus type 1 Sabin had been replaced with sequences derived from the VP1 beta G-beta H loop (antigenic site 1) of FMDV O1 Kaufbeuren (O1K), chimera O1.1 (residues 141 to 154), chimera O1.2 (residues 147 to 156), and chimera O1.3 (residues 140 to 160) or from the beta B-beta C loop of VP1 (antigenic site 3) in chimera O3.1 (residues 40 to 49). One chimera (O1.3) was neutralized by FMDV-specific polyclonal serum and monoclonal antibodies directed against antigenic site 1 of FMDV. Chimeras O1.3 and O3.1 induced site-specific FMDV-neutralizing antibodies in guinea pigs. Chimera O1.3 was capable of inducing a protective response against FMDV challenge in some guinea pigs.

Studies on glycoprotein 13 (gp13) of equid herpesvirus 1 using affinity-purified gp13, glycoprotein-specific monoclonal antibodies and synthetic peptides in a hamster model.

Hamsters were immunized with either an affinity-purified preparation of equid herpesvirus 1 (EHV-1) glycoprotein 13 (gp13) or synthetic peptides representing three sequences within the homologous glycoprotein of EHV-4, resulting in the production of anti-peptide (in the case of peptide-immunized animals) or antivirus antibodies. The sera from gp13-immunized hamsters contained antibodies which showed virus-neutralizing activity and complement-mediated antibody lysis of EHV-1-infected target cells. These hamsters were protected from EHV-1 challenge. The characteristics of a panel of anti-gp13 monoclonal antibodies (P28, P17, 14H7, 16E4 and 16H9) were assessed both in vivo and in vitro. 16E4 and P28 showed high levels of complement-mediated neutralization of virus, complement-mediated lysis of virus-infected target cells and passive protection of hamsters. Furthermore, epitope mapping studies demonstrated that this glycoprotein contains a neutralizing epitope recognized by EHV-1-immune horse serum. The data imply that gp13 has potential as a candidate antigen for a molecular vaccine.

Mouse protection test as a predictor of the protective capacity of synthetic foot-and-mouth disease vaccines.

A passive immunity test (MPT) in suckling mice for the quantification of protective anti-foot-and-mouth disease virus (FMDV) antibodies in serum is described. Comparisons with titres obtained using conventional serum neutralization tests show that for cattle given synthetic peptide vaccines this in vivo assay is a better indicator of protection, while for convalescent animals and virus-vaccinates both tests are equally valid predictors of immune status. Cleavage of Fc fragments from anti-virus or anti-peptide IgG results in a marked decrease in MPT titres although binding to virus in ELISA is unaffected, indicating that intact antibodies are required for in vivo clearance of FMDV. Cross-protection studies demonstrate that anti-peptide sera, while less potent than anti-viral sera in conferring passive immunity against FMDV challenge, have a wider protective range than anti-viral sera within the O serotype and also between O and A serotypes. Possible qualitative differences between anti-viral and anti-peptide sera are discussed in the light of these findings.

A hamster model of equine herpesvirus type 1 (EHV-1) infection; passive protection by monoclonal antibodies to EHV-1 glycoproteins 13, 14 and 17/18.

Following intraperitoneal or intranasal inoculation of the Syrian hamster with equine herpesvirus type 1 (EHV-1), strain Kentucky D, virus replicated in the liver and lungs reaching a peak at 4 days post-infection (p.i.). By day 6 p.i. virus titres in these organs had reduced and the spleen contained virus-specific cytotoxic cells. This cytotoxicity was mediated by T cells since treatment of effector cells with a monoclonal antibody to hamster T lymphocytes inhibited the effect. An antiviral humoral immune response was present by day 4 when antibodies capable of lysing EHV-1-infected target cells in the presence of complement were detected. The transfer of serum from recovered hamsters into naive recipients 24 h before challenge prevented virus infection, whereas serum transferred 24 h after challenge reduced the titre of virus recovered from target organs. Inoculation of hamsters with monoclonal antibodies directed to glycoproteins 13, 14 and 17/18 of a subtype 1 virus (Army 183) before virus challenge protected hamsters. This hamster model will prove useful for studying the immune response to EHV-1 and evaluating the immunogenicity of individual virus components.