Immunization with a peptide mimicking lipoteichoic acid induces memory B cells in BALB/c mice.

BACKGROUND: There is an urgent clinical need for developing novel immunoprophylaxis and immunotherapy strategies against Staphylococcus aureus (S. aureus). In our previous work, immunization with a tetra-branched multiple antigenic peptide, named MAP2-3 that mimics lipoteichoic acid, a cell wall component of S. aureus, successfully induced a humoral immune response and protected BALB/c mice against S. aureus systemic infection. In this study, we further investigated whether vaccination with MAP2-3 can elicit immunologic memory. METHODS: BALB/c mice were immunized with MAP2-3 five times. After one month of the last vaccination, mice were challenged with heat-killed S. aureus via intraperitoneal injection. After a 7-day inoculation, the percentage of plasma cells, memory B cells, effector memory T cells, and follicular helper T cells were detected by flow cytometry. The levels of IL-6, IL-21, IL-2, and IFN-γ were measured by real-time PCR and ELISA. Flow cytometry results were compared by using one-way ANOVA or Mann-Whitney test, real-time PCR results were compared by using one-way ANOVA, and ELISA results were compared by using one-way ANOVA or student's t-test. RESULTS: The percentage of plasma cells and memory B cells in the spleen and bone marrow from the MAP2-3 immunized mice was significantly higher than that from the control mice. The percentage of effector memory T cells in spleens and lymphoid nodes as well as follicular helper T cells in spleens from the MAP2-3 immunized mice were also higher. Moreover, the levels of IL-6 and IL-21, two critical cytokines for the development of memory B cells, were significantly higher in the isolated splenocytes from immunized mice after lipoteichoic acid stimulation. CONCLUSIONS: Immunization with MAP2-3 can efficiently induce memory B cells and memory T cells.

Immunization with a peptide mimicking Lipoteichoic acid protects mice against Staphylococcus aureus infection.

Lipoteichoic acid (LTA), a major component of the cell wall of Staphylococcus aureus (S. aureus), is not generally considered as an ideal vaccine candidate since it is a thymus-independent antigen. In this study, we screened a 12-mer phage peptide library and identified a series of peptide sequences that can mimic the epitope of LTA. A tetra-branched multiple antigenic peptide, named MAP2-3, comprising one of the positive peptide sequences (GHKEDRQWCQHS), was synthesized. Immunization with MAP2-3 induced LTA-specific IgG antibodies, prolonged the survival time, and decreased the bacterial burden in organs of mice infected with S. aureus. Moreover, passive immunization with polyclonal anti-MAP2-3 sera reduced bacterial load in organs of mice with bacteremia, alleviated acute lung injury in mice with pneumonia, and decreased the size of lesions in mice with skin infection. The number of LTA-specific antibody-secreting cells in the spleen of MAP2-3 immunized mice were significantly higher than that in the control mice. In summary, as a surrogate of LTA, vaccination with MAP2-3 elicited humoral immune response and protected mice from S. aureus infection. This study provides a new option to design vaccines against S. aureus.

[A Paralytic shellfish poisoning GTX2,3 mimic peptide isolated from phage display: characterization and potential applications].

AIM: To screen peptide mimics of PSP (Paralytic shellfish poisoning) GTX2,3 from a random 12-mer phage display peptide library and to identify and characterize the specificity and accuracy of the peptide mimotope of GTX2,3. METHODS: The monoclonal antibody against GTX2,3 (mAb E(9);F(10);) was used as a target to screen the 12-mer phage display peptide library and the specificity of phage clones were identified by sandwich ELISA and blocking assay. The peptide sequences of positive phage clones were determined and analyzed by DNA sequencing. The affinity and specificity of synthetic peptide were identified by a competitive ELISA. RESULTS: The 20 clones were identified to be specific reactivity with the mAb E(9);F(10);. Amino acid sequence analysis revealed seven different types of mimotope sequence, most of which contained a common motif DXLXPP(X presents random acid amino), X was random amino acid. The Phage No.2(phage 2), the clone with mimotope sequence WPSLDXLXPPSY showed the strongest binding, and inhibited the reactivity of the mAb with GTX2,3. Another ELISA result showed that synthetic peptide-1 (SP-1) which contain mimotope amino acid sequence was able to inhibit the mAb- GTX2,3 interaction. CONCLUSION: The mimotope peptide of GTX2,3 is obtained by using the phage display technology. The results also showed that SP-1 bind to mAb E(9);F(10); at the same site as GTX2,3.