Enhanced mucosal immunoglobulin A response and solid protection against foot-and-mouth disease virus challenge induced by a novel dendrimeric peptide

Abstract

The successful use of a dendrimeric peptide to protect pigs against challenge with foot-and-mouth disease virus (FMDV), which causes the most devastating animal disease worldwide, is described. Animals were immunized intramuscularly with a peptide containing one copy of a FMDV T-cell epitope and branching out into four copies of a B-cell epitope. The four immunized pigs did not develop significant clinical signs upon FMDV challenge, neither systemic nor mucosal FMDV replication, nor was its transmission to contact control pigs observed. The dendrimeric construction specifically induced high titers of FMDV-neutralizing antibodies and activated FMDV-specific T cells. Interestingly, a potent anti-FMDV immunoglobulin A response (local and systemic) was observed, despite the parenteral administration of the peptide. On the other hand, peptide-immunized animals showed no antibodies specific of FMDV infection, which qualifies the peptide as a potential marker vaccine. Overall, the dendrimeric peptide used elicited an immune response comparable to that found for control FMDV-infected pigs that correlated with a solid protection against FMDV challenge. Dendrimeric designs of this type may hold substantial promise for peptide subunit vaccine development.

FIG. 1.

Serum IgG1- and IgG2-specific responses in pigs following FMDV infection. (A) Peptide-immunized animals. (B) Contact pigs. Titers are expressed as reciprocals of the last dilution of sera (log₁₀), calculated by interpolation to give an A₄₉₂ of 1.0 OD unit. Each bar corresponds to geometric mean of at least two determinations ± standard error. At day 21, pigs 1 to 4 were immunized with a second dose of peptide. Day 49 corresponds to 10 days postchallenge (pigs 1 to 4) or 10 days postcontact (pigs 5 and 6). Day 59 corresponds to 10 days postinoculation for pigs 5 and 6.

FIG. 2.

IgA-specific responses to FMDV. Shown are sera (bars) and nasal fluids (open circles) collected at different days after peptide immunization (pigs 1 to 4) (A) or after contact with peptide-immunized pigs (animals 5 and 6) (B). Mean titers of IgA in sera are expressed as described in the legend to Fig. 1. Titers of IgA in nasal fluids are expressed as the OD at 492 nm (OD₄₉₂) value (shown above each time point) obtained with a 1/10 serum dilution.

FIG. 3.

Specific T-cell responses in peptide-immunized pigs. Samples were collected at days 39 (day of challenge) (A) and 49 (10 days postinfection) (B). Peak lymphoproliferative responses of pigs 1 to 4 to peptide B₄T (20 μg/ml) and to FMDV C-S8c1 (10⁵ TCID₅₀/ml) are shown. Data are shown as SI (see Materials and Methods) and standard deviations are indicated. The cpm obtained in the corresponding control cultures are shown above each bar.

FIG. 4.

In vitro stimulation of cytokines. IFN-γ (A) and IL-10 (B) released by PBMC from peptide-immunized pigs stimulated in vitro with 20 μg/ml of peptide B₄T. Peak values (in pg/ml) were detected by ELISA at 48 h and 72 h of in vitro stimulation for IL-10 and IFN-γ, respectively (see details in Materials and Methods). The detection levels for both cytokines in control cultures (medium alone) were below the sensitivity of the assays (7 pg/ml for IFN-γ and 15 pg/ml for IL-10).