Protection via a ROM4 DNA vaccine and peptide against Toxoplasma gondii in BALB/c mice

Abstract

Background Toxoplasma gondii (T. gondii) is an obligate intracellular protozoan parasite with a broad host range including most warm-blooded animals, including humans. T. gondii surface antigen 1 (SAG1) is a well-characterized T. gondii antigen. T. gondii expresses five nonmitochondrial rhomboid intramembrane proteases, TgROM1-5. TgROM4 is uniformly distributed on the surface of T. gondii and involved in regulating MIC2, MIC3, MIC6, and AMA1 during T. gondii invasion of host cells. Bioinformatics have predicted ROM4 B-cell and T-cell epitopes. Immunization strategy is also a key factor in determining the effectiveness of the immune response and has gained increasing attention in T. gondii vaccine research. In this study, we used a DNA prime-peptide boost vaccination regimen to assess the protective efficacy of various vaccination strategies using TgROM4.MethodsWe identified a polypeptide (YALLGALIPYCVEYWKSIPR) using a bioinformatics approach, and immunized mice using a DNA-prime and polypeptide-boost regimen. BALB/c mice were randomly divided into six groups, including three experimental groups (peptide, pROM4 and pROM4/peptide) and three control groups (PBS, pEGFP-C1 and pSAG1). Mice were then immunized intramuscularly four times. After immunization, IgG and cytokine productions were determined using enzyme-linked immunosorbent assays. The survival time of mice was evaluated after challenge with tachyzoites of T. gondii RH strain. Additionally, the number of cysts in the brain was determined after intragastric challenge with cysts of T. gondii PRU strain.ResultsMice vaccinated with different immunization regimens (peptide, pROM4 and pROM4/peptide) elicited specific humoral and cellular responses, with high levels of IgG, IgG2a, and interferon (IFN)-γ. Moreover, IgG, IgG2a and IFN-γ levels were highest in the pROM4/peptide group. Immunized mice, especially those in the pROM4/peptide group, had prolonged survival times after challenge with tachyzoites and reduced numbers of brain cysts after infection compared with negative controls.ConclusionA DNA prime-peptide boost regimen based on ROM4 elicited the highest level of humoral and cellular immune responses among immunization regimens, and may be a promising approach to increase the efficacy of DNA immunization.

DNA vaccine ROP29 from Toxoplasma gondii containing R848 enhances protective immunity in mice

“…To date, no vaccine has been proven to provide full protection against a T. gondii cyst challenge . Compared with the studies by Zhang et al and Han et al, a remarkable reduction in T. gondii cysts was found in the present study; however, the new combined vaccine still did not provide full protection. Compared with the other experimental mice, R848/pROP29‐immunized mice had fewer cysts in their brains, indicating that the new combined vaccine could successfully stimulate immune protection against a less virulent strain of T. gondii .…”

The Molecular Characterization and Immunity Identification of Rhoptry Protein 22 of Toxoplasma gondii as a DNA Vaccine Candidate Against Toxoplasmosis

“…Ten microliters of brain mixtures from each animal was used to count the number of cysts quantity for thrice (Han et al. ). The size of cysts in each group was observed with a microscope.…”

“…After 1 mo, the survival rate of mice challenged with the PRU strain was determined, and the brains of these animals were removed and ground in 1 ml of PBS. Ten microliters of brain mixtures from each animal was used to count the number of cysts quantity for thrice (Han et al 2017). The size of cysts in each group was observed with a microscope.…”

SAG4 DNA and Peptide Vaccination Provides Partial Protection against T. gondii Infection in BALB/c Mice

“…SAG4 protein expression is upregulated in bradyzoite, which prompted us to evaluate whether SAG4 could elicit effective immune responses against infection with a low virulence strain of T. gondii in the mouse model. According to previous study, SAG1 was believed to be the most promising vaccine candidate because it was regulated through humoral and cellular immune responses ( Kasper and Khan, 1993 ; Cao et al, 2015 ; Han et al, 2017 ). In order to analyze the antigenicity and immunogenicity of SAG4, we used bioinformatics approaches to analyze and compare linear-B cell epitopes and Th-cell epitopes of SAG4 and SAG1.…”