Cellular immunity to nucleoproteins (NP) of Crimean-Congo hemorrhagic fever virus (CCHFV) and Hazara Virus (HAZV).

Crimean-Congo Hemorrhagic Fever Virus (CCHFV) is a globally significant vector-borne pathogen with no internationally-licensed preventative and therapeutic interventions. Hazara virus (HAZV), on the other hand, a related Orthonairovirus, has not been reported as a human pathogen. HAZV has been proposed as a surrogate model for studying CCHFV, bisosafety level 4 (BSL-4) agent. Previously, we investigated the humoral immune responses between NPs of these viruses and in this study, we extended the scrutiny to cellular immune responses elicited by NPs of CCHFV and HAZV. Here, mice were immunized with recombinant CCHFV NP and HAZV NP to evaluate the correlates of cell-mediated immunity (CMI). Delayed-type hypersensitivity (DTH) responses were assessed by challenging immunized mice with CCHFV-rNP or HAZV-rNP on the footpad and lymphocyte proliferation assays (LPAs) were performed by stimulating splenocytes in vitro with CCHFV-rNP or HAZV-rNP to compare cellular immune responses. In all test groups, strong DTH and LPA responses were detected against homologous and heterologous challenging antigens. To assess the cytokine response, an RT-qPCR -specific for cytokine mRNAs was utilized. Interestingly, CCHFV NP stimulated groups exhibited a significantly elevated mRNA level of interleukin 17 A (IL-17) compared to HAZV NP, indicating a notable difference in immune responses. This study presents comparison between CMI elicited by NPs of CCHFV and HAZV and contributes to the understanding of a highly pathogenic virus, particularly in the context of the declaration of CCHFV by World Health Organization's (WHO) as a major viral threat to the world.