Cellular Immune Responses in Acute Hepatitis E Virus Infection to The Viral Open Reading Frame 2 Protein

Hepatitis E virus (HEV) causes acute viral hepatitis and is endemic in the developing world. Few data are available on cellular immune responses in HEV infection. Using flow cytometry, we studied the frequencies of peripheral blood CD4⁺ /CD8⁺ T cells secreting interferon (IFN)-γ, tumor necrosis factor (TNF)-α, and interleukin (IL)-4 in 21 patients with acute hepatitis E and 18 healthy controls, after stimulation with the HEV capsid (ORF2) protein. Cytokine levels in serum specimens and culture supernatants of ORF2-stimulated peripheral blood mononuclear cells (PBMCs) were estimated in enzyme-linked immunosorbent assays. In addition, cytokine mRNA transcripts were measured in PBMCs by reverse transcription-polymerase chain reaction. In patients with acute hepatitis E, although the total CD4⁺ population was expanded, the proportions of CD4⁺/CD69⁺ and CD8⁺ /CD69⁺ cells producing IFN-γ, TNF-α, and IL-4 in response to HEV ORF2 stimulation were unchanged. However, IFN-γ levels in the supernatants and IFN-γ mRNA transcripts in cells were elevated in ORF2-stimulated PBMCs in acute hepatitis E; levels of IL-2 or TNF-α were unchanged. Our findings suggest that CD4⁺ IFN-γ-secreting cells, which do not belong either to the helper T cell type 1 or type 2 phenotype, as is the case with natural killer T cells, may be involved in the pathogenesis of hepatitis E. Further, the limited immune reactivity we detected in peripheral blood cells may be related to the sequestration of immune events to the intrahepatic compartment, which is the major disease site.