Human defined antigenic region on the nucleoprotein of Crimean-Congo hemorrhagic fever virus identified using truncated proteins and a bioinformatics approach.

Crimean-Congo hemorrhagic fever virus (CCHFV) is a tick-borne viral zoonosis widely distributed in Africa, Asia and eastern Europe. In this study, amino acid sequence data for the CCHFV nucleoprotein (NP) was used to identify potential linear epitopic regions which were subsequently included in the design of large and small truncated recombinant NP antigens and peptide libraries. Two truncated recombinant CCHFV NP antigens were prepared based on results of prediction studies to include epitopic regions and exclude hydrophobic regions that could influence protein expression and solubility. Serum samples were collected from acute and convalescent patients. An IgG antibody response was detected in 16/16 samples tested using the large recombinant NP-based ELISA and in 2/16 using the small recombinant NP-based ELISA. A total of 60 peptides covering predicted epitopic regions of the NP were synthesized and peptide NRGGDENPRGPVSR at amino acid position 182-195, reacted with 13/16 human serum samples. In summary, functional assays are required to determine the biological activity of predicted epitopes for development of peptide based assays for antibody detection. Bacterially expressed complete NP antigens have previously been shown to be useful tools for antibody detection. Truncation of the antigen to remove the hydrophobic C terminus had no impact on the ability of the antigen to detect IgG antibody in human sera. The results indicate that the region from amino acids 123 to 396 includes a highly antigenic region of the NP with application in development of antibody detection assays.