Investigation of delayed type hypersensitivity response against crimean-congo hemorrhagic fever virus nucleoprotein

Abstract

Crimean–Congo hemorrhagic fever (CCHF) caused by CCHFV is reported in a wide geographic range with a fatality rate ranging from 5 to 50 %. CCHFV is a member of the family Bunyaviridae and classified in Nairovirus genus. CCHFV genome is composed of tripartite single-stranded negative RNA segments, and RNA dependent viral RNA polymerase is produced by L segment. S segment encodes nucleoprotein (NP) and M segment expresses Gn and Gc. To initiate the viral replication and transcription in the host cell, the segments are needed to be encapsidated by NP. The S segment of CCHFV encodes 53 kDa NP made up of globular domain with a prominent arm. CCHFV infection is generally reported as a mild, nonspecific febrile illness but in some cases, severe hemorrhagic disease is also developed. Persisting hemorrhage, multi-organ failure and shock result in fatality on day 5-14 of illness. In combatting against viral infections, CMI plays a pivotal role. Therefore it is essential to clarify the role of cellular immunity in CCHFV infection. In this study, we aimed to investigate the presence of delayet type hypersensitivity (DTH) reactions against CCHFV in an animal model. For this purpose, CCHFV NP (1449 bp), N-terminal part of NP, NPNT (387 bp) and C-terminal part of NP, NPCT (513 bp) were recombinantly produced in procaryotic expression systems and investigated their effect on DTH. Following immunization steps, antigens were injected in three different dosage (50 μg/μl, 100 μg/μl, 200 μg/μl) and footpad swelling was measured by an electronic caliper. For each protein, DTH response has peaked at 24 hr and decreased by 72 hr. Footpad swelling was statistically significant on right hind pad injected with antigen for each groups, compared to negative control (p<0,05). 100 μg/μl was found to be optimum dose for DTH response. The results of this study demonstrate that, CCHFV NP contains CD4+ T cell epitopes and N-terminal part of CCHFV NP developed stronger antigenicity than C-terminal part. Because, the exact role played by each protein in developing a cellular immunity against the whole virus have not been studied in detail, any information on the individual proteins and on the cellular immune response will be a wellcomed addition to the data on CCHFV. These information would be used in developing strategies in designing vaccines as well as on antiviral approaches.