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- Protective Immune Reponses Induced by Non-infectious L-particles of Equine Herpesvirus Type-1: Implication of Cellular Immunity
- Mohd Lila Mohd Azmi , Hugh John Field , Frazer Rixon , John McLauchlan
- J. Microbiol. 2002;40(1):11-19.
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Abstract
- Mice immunized with equine herpesvirus type-1 (EHV-1) L-particles showed a significant increase (p<0.05) in serum antibody titers. Upon a booster dose four weeks later, antibody titers increased significantly. Interestingly, immunization via intravenous or intramuscular route induced significantly higher (p<0.05) antibody titers. However, mice iummunized with UV-treated L-particles, virions or immunization via intranasal route induced lower antibody titers. Upon challenge inoculation with wild-type EHV-1, our data showed there was a poor correlation between antibody titers and protection against virus replication. Therefore, the role of cell-mediated immunity towards protection was investigated. As predicted, the strongest cell-mediated immunity, as measured by delayed-hypersensitivity test, was detected in mice immunized with live virus particles. The magnitude of cell-mediated immune response correlated with the efficacy of L-particles as immunizing agent. The highest efficacy, as indicated in mice immunized via intranasal route, was highly correlated with cell-mediated immunity. A similar phenomenon was also demonstrated in mice immunized intranasally with UV-treated L-particles. However, the degree of protection was reduced when mice immunized intravenously or intramuscularly with UV-treated L-particles. In conclusion, protection conferred in these animals was highly implicated by immune cells and the least by antibodies. The route of immunization and the nature of the antigen also contributed to the efficacy of L-particles as immunizing agent. In contrast to that of herpes simplex virus type 1, our data showed EHV-1 non-infectious L-particles are highly suitable for immunization of the host against EHV-1 disease.
- Protection of Specific-pathogen-free (Spf) Foals from Severe Equine Herpesvirus Type-1 (Ehv-1) Infection Following Immunization with Non-infectious L-particles
- Mohd Lila Mohd-Azmi , John Gibson , Frazer Rixon , John McLauchlan , Hugh John Field
- J. Microbiol. 2002;40(3):183-192.
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Abstract
- Cells infected with equine herpesvirus type-1 (EHV-1) produced both infectious and non-infectious virus-related particles. Compared to the whole virion, non-infectious particles termed L-particles were determined to lack 150 kDa protein, commonly known as nucleocapsid protein. The potential of L-particles to induce immune responses was studied in mice and foals. Intranasal immunization with L-particles or whole virions induced poor IgG antibody responses in mice. Interestingly, despite the poor antibody response, the conferred immunity protected the host from challenge infections. This was indicated by a significant reduction in virus titers in line with recovery towards normal body weight. Subsequently, the test on the usefulness of L-particles as immunizing agents was extended to foals. Immunization of specific-pathogen-free (SPF) foals resulted in similar results. As determined by a complement-fixing-antibody test (CFT), foals seroconverted when they were immunized either with inactivated L-particles or whole virions via intramuscular (i.m.) injections. The presence of the antibody correlated with the degree of protection. Beyond day 1 post challenge infection (p.i.), there was no virus shedding in the nasal mucus of foals immunized with whole EHV-1 virions. Virus shedding was observed in foals immunized with L-particles but limited to days 6 to 8 p.i. only. In contrast, extended virus shedding was observed in non-immunized foals and it was well beyond day 14 p.i. Viremia was not detected for more than four days except in non-immunized foals. Immunization in mice via intranasal (i.n.) conferred good protection. However, compared to the i.n. route, a greater degree of protection was obtained in foals following immunization via i.m. route. Despite variation in the degree of protection due to different routes of immunization in the two animal species, our results have established significant evidence that immunization with L-particles confers protection in the natural host. It is suggested that non-infectious L-particles should be used as immunizing agents for vaccination of horses against EHV-1 infection.
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