Identification of a linear B-cell epitope within the Bluetongue virus serotype 8 NS2 protein using a phage-displayed random peptide library.

The NS2 protein of Bluetongue virus (BTV) is an important non-structural protein and plays important roles in viral replication and assembly. In this study, one monoclonal antibody (mAb), 4D4, was raised against BTV8 NS2. Phage display technology was used and identified the consensus binding motif SNYD recognized by mAb 4D4. To define the minimal region required for antibody binding, a panel of synthetic peptides encompassing SNYD derived from the BTV8 NS2 was then used to more specifically define the 4D4 epitope as (149)RSNYDV(154). Furthermore, amino acid sequence alignments of different BTV serotypes and other orbiviruses suggested that this epitope is highly conserved among the BTV serotypes. The mAb reagent generated in this study may be applied to the development of BTV diagnosis and surveillance programs and the epitope defined here can lead to important insights into how BTV might interact with the sheep's immune system.

Identification of two novel BTV16-specific B cell epitopes using monoclonal antibodies against the VP2 protein.

The VP2 protein of bluetongue virus (BTV) is an important structural protein and is the principal antigen responsible for BTV serotype specificity. In this study, we mapped the reactivity of two BTV16-specific monoclonal antibodies (MAbs) and identified two novel serotype-specific linear B cell epitopes on the BTV16 VP2 protein. By screening a series of peptides derived from the BTV16 VP2 protein and expressed as mannose-binding protein fusions, we determined that the linear epitopes recognized by the VP2-specific MAbs 3 G10 and 2B4 were located within the peptides 34EWSGHDVTEIPNRRMF49 and 540KNEDPYVKRTVKPIRA555, respectively. To define the minimal region required for antibody binding within these peptide regions, a series of progressively shorter peptides were synthesized and evaluated for 3 G10 and 2B4 binding. This work defined the motifs 34EWSGHDVTEIPNRRMF49 and 543DPYVKRTVK555 as the minimal linear peptides required for 3 G10 and 2B4 binding, respectively. Alignment of amino acid sequences from a number of BTV16 strains isolated from different regions indicated that these two epitopes are highly conserved among BTV16 strains. Furthermore, these two epitopes are not conserved among other BTV serotypes or prototype members of the genus Orbivirus in the family Reoviridae, as shown by sequence alignments. The MAb reagents and linear epitopes defined here provide the basis for the development of epitope-based serotype-specific differential diagnostic tools and may be useful in the design of epitope-based vaccines.

Identification of three novel linear B-cell epitopes on the VP5 protein of BTV16.

Bluetongue virus (BTV) VP5 protein is an important antigenic protein which is centrally involved in serotype determination and the virus entry process. Very little is known about the B-cell epitopes on the BTV VP5 protein recognized by humoral immune responses. In this study, we generated five BTV16 VP5 protein-specific monoclonal antibodies (MAbs), named 3B11, 2B10, 1H7, 4A6 and 3G9, and defined the linear epitopes recognized by MAbs using a series of peptides expressed as maltose-binding protein (MBP)-fusion polypeptides. Three novel linear B-cell epitopes were identified: 3B11 and 3G9 recognized the motif ITANTREIQHIKEE; 2B10 recognized the motif LSGID; and 4A6 recognized the motif STMVKEYRQKIDALKA. Exact sequences corresponding to the three motifs identified were found in the BTV16 VP5 protein ((310)ITANTREIQHIKEE(323), (265)LSGID(269) and (188)STMVKEYRQKIDALKA(203)). These motifs represent the minimal linear peptide sequence required for MAb reactivity, as binding of each MAb was abolished when additional amino acids were removed from the amino and carboxy termini of the peptide. Amino acid sequence alignment indicated that three epitopes were totally conserved among different BTV16 strains. The MAbs generated along with identified epitopes will be useful for examining VP5 protein function and the development of epitope-based marker vaccines against BTV.

Monoclonal antibodies against VP7 of bluetongue virus.

VP7 is a major group-specific protein of the bluetongue virus (BTV), and is therefore a candidate for use as a diagnostic reagent. In this study, BALB/c mice were immunized with BTV16, and the lymphocyte hybridoma technique and indirect ELISA screening method were employed to obtain two strains of hybridoma cells secreting specific monoclonal antibodies (MAbs) to BTV16. Eukaryotic recombinant plasmids coding for 10 segments of BTV16 separately were transfected into BHK-21 cells, respectively, followed by immunofluorescence, showing that two MAbs only reacted with BTV-VP7. Western blot analysis showed the same result. Indirect immunofluorescence results indicated that two of the MAbs present different response spectrums with BTV1~24 serotypes. These results indicate that these MAbs may be good candidates for a specific diagnostic method and functional exploration of the VP7 protein.