Epitope-mapping of the glycoprotein from Crimean-Congo hemorrhagic fever virus using a microarray approach

<div><p>Crimean-Congo hemorrhagic fever virus (CCHFV) causes severe acute human disease with lethal outcome. The knowledge about the immune response for this human health threat is highly limited. In this study, we have screened the glycoprotein of CCHFV for novel linear B-cell epitopic regions using a microarray approach. The peptide library consisted of 168 synthesized 20mer peptides with 10 amino acid overlap covering the entire glycoprotein. Using both pooled and individual human sera from survivors of CCHF disease in Turkey five peptide epitopes situated in the mucin-like region and GP 38 (G15-515) and G_N G516-1037 region of the glycoprotein were identified as epitopes for a CCHF immune response. An epitope walk of the five peptides revealed a peptide sequence located in the G_N region with high specificity and sensitivity. This peptide sequence, and a sequence downstream, reacted also against sera from survivors of CCHF disease in South Africa. The cross reactivity of these peptides with samples from a geographically distinct region where genetically diverse strains of the virus circulate, enabled the identification of unique peptide epitopes from the CCHF glycoprotein that could have application in development of diagnostic tools. In this study clinical samples from geographically distinct regions were used to identify conserved linear epitopic regions of the glycoprotein of CCHF.</p></div

Reactivity of pooled South African sera.

<p>Four CCHFV survivor pools (red) and one uninfected pool (black)) against 168 peptides representing the complete precursor glycoprotein of CCHFV (Turkish strain).</p

Reactivity of pooled Turkish sera.

<p>Reactivity of eight CCHFV survivor pools (blue) and six uninfected pools (black) against 168 peptides representing the complete precursor glycoprotein of CCHFV (Turkish strain, Kelkit06, Uniprot #C7F6X8).</p

Sequences of scan peptides that showed significant reactivity with pooled Turkish sera of CCHFV survivors (1–14) and with control sera (15–20).

<p>Five possible epitopes (6, 7, 12, 13 and 14) were selected for further evaluation using a single-amino acid epitope walk analysis.</p

Dot-plot after combining intensities of serology with peptide p55 and p96 or EWP p83 (p96 + 3 aa).

<p>Control sera from healthy individuals, Turkish CCHFV survivors and South African CCHFV survivors. The dotted line represents the diagnostic cut-off value. P<0.0001.</p

Strain similarity, comparison of amino acid sequences from eight strains of CCHFV from South Africa and one strain of CCHFV from Turkey.

<p>Sequence data was retrieved from UniProt. Amino acid differences are bolded.</p

Dot-plot of intensities of the selected peptide 55 (⁵⁴¹ETAEIHDDNYGGPGDKITIC⁵⁶⁰) after serology.

<p>This included sera from Turkish CCHFV survivors, control sera from individuals infected with other viral pathogens as controls and Bulgarian indivduals vaccinated against CCHFV. The dotted line represents the diagnostic cut-off value. P<0.0001.</p

Dot-plot of intensities of the selected peptide EWP 83 (p96 + 3 aa, ⁹⁵⁴LAVCKRMCFRATIEASRRAL⁹⁷³) after serology.

<p>This includes sera from Turkish CCHFV survivors, control sera from individuals infected with other viral pathogens as controls and Bulgarian individuals vaccinated against CCHFV. The dotted line represents the diagnostic cut-off value determined from mean of the control group plus two standard deviations. P<0.0001.</p

Epitope walk (EW) of selected five peptides (p24, p55, p56, p78 and p96).

<p>Figure illustrates the RFU of individual serum samples from CCHFV survivors from Turkey to selected peptides. Epitope walk sequences are found in <a href="http://www.plosntds.org/article/info:doi/10.1371/journal.pntd.0006598#pntd.0006598.s003" target="_blank">S3 Table</a>. In general two different patterns were seen when screening the epitopes (colored in blue and orange).</p

Reactivity of Turkish (n = 30) and South African sera (n = 41) against nine selected peptides.

<p>Reactivity of Turkish (n = 30) and South African sera (n = 41) against nine selected peptides.</p