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Published on: December 9, 2014
Augmentation of resistance to toxoplasma in mice by pretreatment with attenuated vaccine
Abstract:
It is well known that certain chronic infectious diseases can be cured by preimmunization of the host against the live vaccine of an attenuated strain of an infectious agent from an attack of a virulent strain of same group of infectious agents. To test for the existence of a similar protective mechanism for Toxoplasma infection in mice, seven groups of mice were first infected with two kinds of low virulence strains (Beverley or S-273). They were challenged with a strong virulence strain (RH) from 2 to 59 weeks after the first immunization. All mice in one group challenged 2 to 3 weeks after the first Beverley immunization survived at rates of 33, 22 and 18 percent respectively, and mice examined at almost the same times after immunization with S-273 showed survival rates of 35, 19 and 52 percent respectively, which indicates a major difference in the number of surviving mice examined after 46-59 weeks. However, the majority of mice killed by a challenge with a virulent strain of Toxoplasma showed prolonged survival times of up to 10 days more than the non-immunized mice. Histological studies of dead mice showed acute bronchitis and/or bronchopneumonia, and a small number of tachyzoites was found in their lungs and other organs. All surviving mice harbored RH parasites in their brains. The present study suggested that mice treated with live vaccine of attenuated Toxoplasma acquired resistance against a challenge of a virulent strain of Toxoplasma. Since the infected mice showed small numbers of parasites and high antibody titers, the cause of death of premunitive mice from highly virulent Toxoplasma might differ from that of non-immune mice.
Insights
Pre-immunization with attenuated Toxoplasma strains in mice conferred resistance against virulent strains. This study suggests a protective mechanism similar to other infectious diseases, with implications for Toxoplasma vaccine development.
Area of Science:
- Immunology
- Infectious Diseases
- Parasitology
Background:
- Pre-immunization with live attenuated vaccines is known to protect against chronic infectious diseases.
- The existence of a similar protective mechanism for Toxoplasma gondii infection has not been well-established.
Purpose of the Study:
- To investigate whether pre-immunization with attenuated Toxoplasma strains confers resistance against a virulent challenge in mice.
- To explore the survival rates and pathological outcomes in mice following challenge with a virulent Toxoplasma strain after varying immunization periods.
Main Methods:
- Seven groups of mice were infected with low-virulence Toxoplasma strains (Beverley or S-273).
- Mice were subsequently challenged with a high-virulence strain (RH) at intervals ranging from 2 to 59 weeks post-immunization.
- Survival rates, survival times, and histopathological findings were analyzed.
Main Results:
- Mice challenged 2-3 weeks post-immunization showed varying survival rates (18-52%) depending on the attenuated strain used.
- The majority of mice that succumbed to the virulent challenge exhibited prolonged survival (up to 10 days longer) compared to non-immunized controls.
- Histological examination revealed acute bronchitis/bronchopneumonia, with tachyzoites found in lungs; surviving mice harbored parasites in their brains.
Conclusions:
- Mice pre-immunized with live attenuated Toxoplasma strains demonstrated acquired resistance against a virulent challenge.
- The observed differences in parasite load and antibody titers suggest distinct mortality mechanisms in premunitive versus non-immune mice infected with virulent Toxoplasma.
