Antigenic and immunogenic investigation of B-cell epitopes in the nucleocapsid protein of peste des petits ruminants virus

Attempts were made to identify and map epitopes on the nucleocapsid (N) protein of peste des petits ruminants virus (PPRV) (Nigeria75/1 strain) using seven monoclonal antibodies (MAbs) and deletion mutants. At least four antigenic domains (A-I, A-II, C-I, and C-II) were identified using the MAbs. Domains A-I (MAb 33-4) and A-II (MAbs 38-4, P-3H12, and P-13A9) were determined to be located on the amino-terminal half (amino acids aa] 1 to 262), and domains C-I (P-14C6) and C-II (P-9H10 and P-11A6) were within the carboxy-terminal region (aa 448 to 521). Nonreciprocal competition between A-II MAbs and MAbs to C-I and C-II domains was observed, indicating that they may be exposed on the surface of the N protein and spatially overlap each other. Blocking or competitive enzyme-linked immunosorbent assay studies using PPRV serum antibodies revealed that epitopes on the domains A-II and C-II were immunodominant, whereas those on the domains A-I and C-I were not. The competition between MAb and rinderpest virus (RPV) serum antibodies raised against RPV strain LATC was found in two epitopes (P-3H12 and P-13A9) on the domain A-II, indicating that these epitopes may cause cross-reactivity between PPRV and RPV. Identification of immunodominant but PPRV-specific epitopes and domains will provide the foundation in designing an N-protein-based diagnostic immunoassay for PPRV.