Abstract
Neospora caninum, an obligate intracellular protozoan, is the major cause for neosporosis and brings serious economic losses to cattle breeding industries worldwide. After invasion, dense granules proteins are abundantly secreted and being important components of parasitophorous vacuole and intravacuolar network where N. caninum survives and replicates. The aim of the present study was to evaluate the protective immunity induced by DNA vaccines with genes encoding dense granules proteins 1 (GRA1), GRA4, GRA9, GRA14, GRA17, and GRA23 against N. caninum tachyzoites in BALB/C mice. Eukaryotic expressing plasmids of pcNcGRAs were constructed and the mice were intramuscularly immunized with pcNcGRAs followed by challenging infection with lethal doses of N. caninum. Immune responses were evaluated through monitoring the levels of serum antibodies, measurement of lymphocyte proliferation, and secretion of cytokines. Immune protection assays were carried out through monitoring survival time, body weight, and parasite burden in the brains. Results showed that all the pcNcGRA DNA vaccines could trigger remarkably specific humoral and cellular responses, with higher levels of IgG and IgG2a antibodies as well as obviously increased secretion of Th1-type IFN-γ cytokines. The immune protective efficacy revealed that pcNcGRA4, pcNcGRA14, and pcNcGRA17 DNA vaccines could individually increase the survival rate to 50, 37.5, and 25% in comparison with 0% in the control group; prolong the survival time more than 20.88 ± 11.12, 18.88 ± 10.83, and 16.63 ± 10.66 days compared with the control group of 4 ± 1.31 days; and decrease parasite burden in the brains to 297.63 ± 83.77, 471.5 ± 110.74, and 592.13 ± 102.2 parasites/100 ng comparing with 1221.36 ± 269.59 parasites/100 ng in the control group. These findings indicated that NcGRA4, NcGRA14, and NcGRA17 are potential vaccine candidates; NcGRA4 displayed better performance in immune protective efficacy and could be further combined with other advantageous antigens applied to the development of safe and effective DNA vaccines against N. caninum.
Highlights
The present study aims to screen excellent DNA vaccine targets by evaluating humoral and cellular immune responses triggered by various reported N. caninum GRA proteins, including granules proteins 1 (GRA1), GRA4, GRA9, GRA14, GRA17, and GRA23, through individual immunization with eukaryotic plasmids of pcNcGRA1, pcNcGRA4, pcNcGRA9, pcNcGRA14, pcNcGRA19, and pcNcGRA23 in BALB/c mice, and its immune protective efficacy after challenging with lethal doses of N. caninum tachyzoites
The present study evaluated the protective immunity of DNA vaccines encoding GRA1, GRA4, GRA9, GRA14, GRA17, and GRA23 of N. caninum in mice for the first time
The present study evaluated the immunogenicity and potency of NcGRA1, NcGRA4, NcGRA9, NcGRA14, NcGRA17, and NcGRA23 using BALB/c mice as models
Summary
The present study aims to screen excellent DNA vaccine targets by evaluating humoral and cellular immune responses triggered by various reported N. caninum GRA proteins, including GRA1, GRA4, GRA9, GRA14, GRA17, and GRA23, through individual immunization with eukaryotic plasmids of pcNcGRA1, pcNcGRA4, pcNcGRA9, pcNcGRA14, pcNcGRA19, and pcNcGRA23 in BALB/c mice, and its immune protective efficacy after challenging with lethal doses of N. caninum tachyzoites. Our findings would lay a foundation for future research on providing new targets for DNA vaccine development
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