Two epitopes shared by Taenia crassiceps and Taenia solium confer protection against murine T. crassiceps cysticercosis along with a prominent T1 response

Abstract

Taenia crassiceps recombinant antigens KETc1 and KETc12 have been shown to induce high level of protection against experimental murine T. crassiceps cysticercosis, an experimental model successfully used to test candidate antigens for use in vaccination against porcine Taenia solium cysticercosis. Based on the deduced amino acid sequence, KETc1 and KETc12 were chemically synthesized in linear form. Immunization with KETc1 induced 66.7 to 100% protection against murine cysticercosis, and immunization with KETc12 induced 52.7 to 88.1% protection. The elicited immune response indicated that both peptides contain at least one B-cell epitope (as demonstrated by their ability to induce specific antibodies) and one T-cell epitope that strongly stimulated the proliferation of T cells primed with either the free peptide or total cysticercal T. crassiceps antigens. The high percentage of spleen cells expressing inflammatory cytokines points to the likelihood of a T1 response being involved in protection. The protective capacity of the peptides and their presence in all developmental stages of T. solium point to these two epitopes as strong candidates for inclusion in a polyepitopic synthetic vaccine against T. solium pig cysticercosis.

FIG. 1

Antibody levels determined by ELISA in individual control (C) and immunized (I) mice against TcAg. The mean level of antibodies was significantly higher in immunized mice than in controls. O.D., optical density.

FIG. 2

Immunofluorescent staining of T. crassiceps (A, C, E, and G) and T. solium (B, D, F, and H) cysticerci. Sections of 6 μm were processed and incubated with pooled sera from noninfected mice (A and B), T. crassiceps-infected mice (C and D), and KETc1-immunized (E and F) and KETc12-immunized (G and H) mice. The tegument (t) and the parenchyma (p) are evident in both cysticerci (C and D). In T. crassiceps cysticerci (E), KETc1 antigen shows a protruding and intensely positive signal in the tegument, while in T. solium cysticerci (F) it is clearly evident in the cuticular folds of the spiral canal (cf). KETc12 is quite abundant in both metacestodes; it is evident in the tegument and in the parenchyma of T. crassiceps (G) as well as in the tegument, parenchyma, and flame cells (arrows) of T. solium (H). Bar, 40 μm.

FIG. 3

Immunofluorescence staining of the T. solium oncosphere (A, C, E, and G) and proglottid tegument (B, D, F, and H). Sections of 6 μm were processed and incubated with pooled sera from noninfected mice (A and B), T. crassiceps-infected mice (C and D), and KETc1-immunized (E and F) and KETc12-immunized (G and H) mice. It is evident that the oncosphere (o) and the distal cytoplasm region (dc) (C and D, respectively) stain positively. Some structures of the perinuclear cytoplasm region (pe), like the protoplasmic extensions of the tegumental cells, are also apparently positive. KETc1 antigen is almost negative in the oncosphere and appears as little positive spots (arrows); in contrast, in adult tissue (F) it is quite evident in the distal cytoplasm region of the tegument. The KETc12 antigen is only slightly present in the oncosphere (o) but is quite conspicuous in the distal cytoplasm region and in the perinuclear cytoplasm region of the adult tissue. Bar, 40 μm.

FIG. 4

Flow cytometer analysis of spleen cells from KETc1- and KETc12-immunized mice with or without in vitro stimulation with the respective peptide or antigen (TcAg) R1 denotes the region of proliferating cells in the SSC/FSC plot (side-scatter/forward-scatter plot), and the number below indicates the percentage of cells in this region. CD4⁺ and CD8⁺ cell percentage expression was determined in the defined R1 gate.