Amino Terminal Region of Crimean‐Congo Hemorrhagic Fever Virus ( CCHFV ) Nucleocapsid ( NP ) Protein Contains Dominant Epitopes Recognised by Cellular Immunity

Crimean-Congo hemorrhagic fever virus (CCHFV) is a tick-borne orthonairovirus associated with severe hemorrhagic fever and high mortality in humans. The genome is comprised of three segments of single-stranded, negative-sense RNA. The nucleocapsid (NP) protein, which is the focus of our study, encoded by the smallest (S) segment, plays a central role in viral RNA encapsidation and is known to be highly immunogenic, eliciting innate, humoral and cellular immune responses. This study aimed to identify the immunodominant regions of the NP that trigger T cell-mediated immune responses. To this end, three truncated variants of the NP from the CCHFV Kelkit'06 strain [NPdelN(1-135 aa), NPdelM(136-295 aa) and NPdelC(296-482 aa)] as well as the full-length NP(1-482 aa) were tested. Following mice immunisations, local lymph node cells were used as the source of lymphocytes and these cells were assessed to gauge the T cell responses. Stimulated splenocytes were analysed for lymphoproliferative responses and cytokine mRNA expression to evaluate T cell polarisation. Based on the data obtained, it appears that the amino-terminal region (1-135 amino acids) of NP is significantly more immunogenic than the other regions. In contrast, the carboxy-terminal region (296-482 aa) appears to play a suppressive role in cellular immune activation. Additionally, the middle region (136-295 aa) of the NP is identified as being responsible for inducing Th17-type cellular immune responses. In conclusion, this study points out to the specific regions of the CCHFV NP that are involved in shaping the cellular immune responses, representing a crucial step toward refining the structural elements contributing anti-viral immunity and providing a sound ground for modulation efforts.