Cellular Immune Responses Against γ-Inactivated Antigen in the Recovered Cases of Kyasanur Forest Disease

Kyasanur Forest Disease Virus (KFDV) is a tick-borne flavivirus that causes life-threatening hemorrhagic fever in humans with case fatality rates of 3-5%. Relatively little is known about the mechanism of its pathogenesis or host immune responses to KFDV infection. Here, we investigated KFDV-specific cellular immune responses in the recovered cases of Kyasanur Forest Disease (KFD). Peripheral blood mononuclear cells of the recovered KFD cases and healthy controls were exposed to γ-inactivated KFDV antigen ex vivo. The proliferation index was determined using an enzyme-linked immunosorbent assay-based lymphoproliferative assay. The frequencies of CD4⁺ and CD8⁺ T cells expressing intracellular interferon (IFN)-γ in response to stimulation with γ-inactivated KFDV antigen were determined using flow cytometry. A significant increase in lymphoproliferation and a high frequency of CD4⁺ and CD8⁺ T cells secreting IFN-γ against γ-inactivated KFDV antigen were found in the recovered KFD group compared to the healthy control group. In conclusion, the study indicated the generation of cellular immune responses in individuals who recovered from KFD and can be used as indicators of cellular immunity in KFD vaccine studies.