Abstract
We have developed and evaluated an immunodominant respiratory syncytial virus (RSV) F antigen in a mouse model. The antigenic region corresponding to amino acids 255–278 of the RSV F protein was cloned into a vector containing the ctxA2B gene of cholera toxin (CT). The recombinant protein was expressed in Escherichia coli and analyzed on sodium dodecyl sulfate–polyacrylamide gels. The purified protein was evaluated by immunoblot and ganglioside GM1 enzyme-linked immunosorbent assay to confirm the expression of the RSV F protein and to correct association of the recombinant protein to form a holotoxin-like chimera, respectively. We hypothesized that genetic fusion of modified CT-based adjuvant with RSV F immunodominant epitopes (rRF-255) would induce protective humoral and cellular immune responses in mice. Intranasal immunization of mice with rRF-255 overall induced higher concentrations of anti-RSV F-specific antibodies in both serum and saliva as compared with mice immunized intranasally with RSV or phosphate-buffered saline (PBS). Antibody isotype analysis (IgA, IgG1, IgG2a, and IgG2b) was also performed. The predominant IgG2a antibody isotype response in combination with cytokine analysis of helper T cell type 1 (interferon-γ, interleukin [IL]-2, IL-12 p70, and tumor necrosis factor-α) and helper T cell type 2 (IL-4 and IL-10) responses revealed that rRF-255 antigen induces a prominent helper T cell type 1 immune response in mice. The rRF-255 antigen also induced serum neutralizing antibodies in immunized mice. Analysis of RSV load in lungs showed that rRF-255 immunization provided significant protection compared with PBS control animals.
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