Evaluation of the adjuvant effect of pidotimod on the immune protection induced by UV-attenuated Toxoplasma gondii in mouse models

Abstract

The current anti-Toxoplasma gondii drugs have many shortcomings and effective vaccines against T. gondii may contribute to the control of this pathogen. Pidotimod is a synthetic substance capable of stimulating both cellular and humoral immunity. To investigate the possible adjuvant effect of pidotimod on the immune response to T. gondii in Kunming mice induced by ultraviolet-attenuated T. gondii (UV-T.g), in this study, mice were immunized intraperitoneal (i.p.) with UV-T.g or UV-T.g co-administered with pidotimod (UV-T.g + PT). After infection or challenge by i.p. injection of 10(2) RH tachyzoites, the animal survival rate, parasite burden in peritoneal lavage fluids, liver histopathology, the level of serum anti-toxoplasma IgG antibody, and the mRNA expressions of IL-2, IFN-γ, and TNF-α from spleen analyzed using real-time PCR, were compared among different groups. The results showed that, compared with infected controls, infected mice treated with pidotimod had significantly increased survival rate and extended survival time, decreased parasite burden, improved liver histopathology, increased level of anti-toxoplasma IgG antibody, and increased mRNA expressions of Th1-type cytokine (IL-2, IFN-γ, and TNF-α) (P < 0.01), while mice vaccinated with UV-T.g and then challenged had even significantly increased survival rate and extended survival time, decreased parasite burden, improved liver histopathology, and increased mRNA expressions of Th1-type cytokines (IL-2, IFN-γ, and TNF-α) (P < 0.01); furthermore, vaccinated mice co-administered with pidotimod had even more lower parasite burden, milder liver histopathology, and higher levels of Th1-type cytokine and anti-toxoplasma IgG antibody (P < 0.01). Our data demonstrated that pidotimod in vivo could promote strong and specific humoral and cellular immune response to T. gondii challenge infection when co-administered with UV-attenuated T. gondii. It suggests that pidotimod may have the potential to be used as an effective vaccine adjuvant.

One minute ultraviolet exposure inhibits Toxoplasma gondii tachyzoite replication and cyst conversion without diminishing host humoral-mediated immune response

“…Our data are largely consistent with prior studies that utilized UV inactivation of T. gondii tachyzoites (Endo, et al, 1981, Grimwood, 1980, Lu, et al, 1999, Yang, et al, 2010, Zhao, et al, 2013). For example, we also showed that tachyzoites exposed to UV were able to exclude Trypan blue, suggesting irradiation did not damage the tachyzoite membrane (Grimwood, 1980).…”

“…We found that 1 minute UV-exposed tachyzoites did not replicate in vitro, as has been seen by others using UV inactivation of tachyzoites (Endo, et al, 1981, Grimwood, 1980). In addition, we report that mice administered inactivated parasites had a robust serological IgG response without a decrease in body weight, as has been previously published (Yang, et al, 2010, Zhao, et al, 2013). …”

“…In addition, while prior studies using UV inactivation have only measured anti-Toxoplasma IgG levels (Yang, et al, 2010, Zhao, et al, 2013), we also evaluated cytokine expression in the brain and spleen. Consistent with prior reports, we found that infection with live tachyzoites can up-regulate expression of the cytokines IL-12β and IL-1β (Hunter, et al, 1995, Yarovinsky and Sher, 2006).…”

“…Current published protocols are based on a rather prolonged exposure to UV irradiation (i.e. up to 60 minutes) (Lu, et al, 1999, Zhao, et al, 2013), without clear demonstration that the inactivated tachyzoites are able to stimulate the host immune system in the absence of parasite replication or cyst production in rodent brains (Endo, et al, 1981, Grimwood, 1980, Lu, et al, 1999, Yang, et al, 2010, Zhao, et al, 2013). Here we describe a new rapid and effective method for UV inactivation of T. gondii tachyzoites in just 1 minute.…”

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“…It is capable of stimulating humoral and cellular immunity 2 , activate natural killer cell, enhance the phagocytic function of macrophage and neutrophilic granulocyte, promote the proliferation of lymphocyte induced by mitogens, and increase the production of cytokines such as Interleukin 2 and γ-interferon 3,4,5 .…”