Niosomes as a vehicle for excretory/secretory antigens enhance immunization efficacy of Toxoplasma gondii vaccine

Abstract

Till now, there is no well-established vaccine for toxoplasmosis in humans. This study evaluated the efficacy of niosomes to enhance the immunogenicity of Toxoplasma gondii excretory/secretory antigens (ESAs) vaccine in mice. The mice were divided into the following groups: group I (naïve), group II (naïve challenged), group III (alum), group IV (niosomes), group V (ESAs), group VI (ESAs and alum) and group VII (ESAs-loaded niosomes). All immunized mice received three doses of vaccine intraperitoneally two weeks apart. Two weeks later, mice were challenged with intraperitoneal injection of 10³ viable tachyzoites of virulent RH strain. Parasitological, histopathological, and immunological studies were done. ESAs-loaded niosomes offered the best protection as they significantly decreased the mean parasitic count in liver and spleen with reduction rates of 85 and 90 %, respectively. Also, it reduced efficiently the inflammation and parenchymal injury in liver with intense iNOS immunostaining expression. In addition, it was effective in stimulation of humoral and cellular immune responses evidenced by the high significant anti-Toxoplasma IgG, increasing of CD4⁺ and CD8⁺ percentages by flowcytometry and serum IFN-γ levels. Therefore, niosomes were proved to be promising vaccine candidates due to enhancing the antigenicity of ESA and their long acting antiparasitic effect.