Sm-p80-based DNA vaccine formulation induces potent protective immunity against Schistosoma mansoni

Abstract

No effective vaccine exists for the human parasitic disease, schistosomiasis. We have targeted a functionally important antigen, Sm-p80 as a vaccine candidate because of its consistent immunogenicity, protective potential and important role in the immune evasion process. In this study we report that a Sm-p80-based DNA vaccine formulation confers 59% reduction in worm burden in mice. Animals immunized with Sm-p80-pcDNA3 exhibited a decrease in egg production by 84%. Sm-p80 DNA elicited strong immune responses that include IgG2A and IgG2B antibody isotypes in vaccinated animals. Splenocytes proliferated in response to Sm-p80 produced appreciably more Th1 response enhancing cytokines (IL-2, IFN-gamma) than Th2 response enhancing cytokines (IL-4, IL-10). These data reinforce the potential of Sm-p80 as an excellent vaccine candidate for schistosomiasis.

Figure 1

Titers of anti-Sm-p80 antibodies in immunized mice. ELISA was performed with a pool of sera obtained by mixing equal volumes of serum collected from each mouse(biweekly) in their respective groups (VR1020 and Sm-p80-VR1020). IgG (A), IgG1 (B) IgG2a (C), IgG2b (D) IgG3 (E) IgM(F) and IgA (G).The value represent the mean of three experiments ± standard error. Statistic significance (P<0.05) are indicated by (*) compared with VR1020 control group.

Figure 1

Titers of anti-Sm-p80 antibodies in immunized mice. ELISA was performed with a pool of sera obtained by mixing equal volumes of serum collected from each mouse(biweekly) in their respective groups (VR1020 and Sm-p80-VR1020). IgG (A), IgG1 (B) IgG2a (C), IgG2b (D) IgG3 (E) IgM(F) and IgA (G).The value represent the mean of three experiments ± standard error. Statistic significance (P<0.05) are indicated by (*) compared with VR1020 control group.

Figure 1

Titers of anti-Sm-p80 antibodies in immunized mice. ELISA was performed with a pool of sera obtained by mixing equal volumes of serum collected from each mouse(biweekly) in their respective groups (VR1020 and Sm-p80-VR1020). IgG (A), IgG1 (B) IgG2a (C), IgG2b (D) IgG3 (E) IgM(F) and IgA (G).The value represent the mean of three experiments ± standard error. Statistic significance (P<0.05) are indicated by (*) compared with VR1020 control group.

Figure 1

Titers of anti-Sm-p80 antibodies in immunized mice. ELISA was performed with a pool of sera obtained by mixing equal volumes of serum collected from each mouse(biweekly) in their respective groups (VR1020 and Sm-p80-VR1020). IgG (A), IgG1 (B) IgG2a (C), IgG2b (D) IgG3 (E) IgM(F) and IgA (G).The value represent the mean of three experiments ± standard error. Statistic significance (P<0.05) are indicated by (*) compared with VR1020 control group.

Figure 2

Levels of cytokine production by splenocytes after 48 hr stimulation with recombinant Sm-p80 in vitro. Groups of mice were inoculated with VR1020 and Sm-p80-VR1020. Data are shown as mean ± S.D. Statistical significance (P<0.05) are indicated by (*) compared with VR1020 control group using independent sample t- test.

Figure 3

RT-PCR for cytokine expression by splenocytes after 24 hr stimulation with recombinant Sm-p80 in vitro. Panels 1, and 3, control groups inoculated with VR1020; Panels 2, 4, experimental groups inoculated with Sm-p80-VR1020. 1, 2, medium control; 3,4, splenocytes stimulated with recombinant Sm-p80.

Figure 4

Fold relative difference of cytokine mRNA level by splenocytes after 24 hr stimulation with recombinant Sm-p80 in vitro. The fold difference was calculated by comparing the differences in the message levels of the control group (VR1020) with the experimental group (Sm-p80-VR1020) after standardization using respective GAPDH.