The GapC protein is highly conserved surface dehydrogenase among Streptococcus dysgalactiae (S. dysgalactiae) and is shown to be involved in bacterial virulence. Immunization of GapC protein can induce specific CD4(+) T-cell immune responses and protect against S. dysgalactiae infection. However, there are no studies to identify immunodominant CD4(+) T-cell epitopes on GapC protein. In this study, in silico MHC affinity measurement method was firstly used to predict potential CD4(+) T-cell epitopes on GapC protein. Six predictive 15-mer peptides were synthesized and two novel GapC CD4(+) T-cell epitopes, GapC63-77 and GapC96-110, were for the first time identified using CD4(+) T-cells obtained from GapC-immunized BALB/c (H-2(d)) and C57BL/6 (H-2(b)) mice spleen based on cell proliferation and cytokines response. The results showed that peptides containing 63-77 and 96-110 induced significant antigen-specific CD4(+) T-cells proliferation response in vivo. At the same time, high levels of IFN-γ and IL-17A, as well as moderate levels of IL-10 and IL-4 were detected in CD4(+) T-cells isolated from both GapC and peptide-immunized mice in vivo, suggesting that GapC63-77 and GapC96-110 preferentially elicited polarized Th1/Th17-type responses. The characterization of GapC CD4(+) T-cell epitopes not only helps us understand its protective immunity, but also contributes to design effective T-cell epitope-based vaccine against S. dysgalactiae infection.
Keywords: CD4(+) T-cell epitope; GapC; Streptococcus dysgalactiae.
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