Specific cellular immune response in hepatitis E patients.

AIMS: To evaluate the specific T cell response together with IgM anti-hepatitis-E-virus (HEV) antibodies in acute hepatitis E (HE) patients. METHODS: Blood samples were collected from 11 HE patients every week and assayed for routine blood investigation after onset of disease until their convalescence. Peripheral blood mononuclear cells were separated from some of the blood samples (1-3 samples per patient) and tested for specific T cell response by enzyme-linked immunosorbent spot assay and IgM anti-hepatitis E virus by enzyme-linked immunosorbent assay. RESULTS: A particulate HEV capsid protein, HEV 239, effectively stimulated the response of T cells from HE patients infected by type 1 or type 4 HEV. In acute HE, a burst of HEV-specific cellular immune response occurred, which decreased along with the decreasing IgM anti-HEV antibody titre and normalization of liver function. CONCLUSIONS: HEV open reading frame 2 amino acids 368-606 can effectively stimulate the HEV-specific T cell response in vitro; the specific T cell response decreases along with convalescence and may play a role in the pathogenesis of acute HE and recovery.

Difference of T cell and B cell activation in two homologous proteins with similar antigenicity but great distinct immunogenicity.

The candidate particulate hepatitis E vaccine, HEV 239, has been shown to be an efficacious vaccine in primates, and clinical study to date shows it to be safe and immunogenic for humans. The antigenicity of HEV 239 is virtually identical to its N-terminal 26 amino acids truncated protein, E2, which is not particulate but soluble. However, HEV 239 is over 200 times more immunogenic than E2. In present study, several events underlying this dramatic immunogenicity difference have been addressed. (1) HEV 239 can efficiently evoke a vigorous and predominant T cell response while E2 cannot induce detectable T cell response; (2) the dominant T cell epitopes in HEV 239 are identified, and both are also contained integrally in E2; (3) priming mice with Th epitope peptide can partially rescue the weak immunogenicity of E2 in alum adjuvant and (4) HEV 239 but not E2 can induce significant antibody response in athymic mice, which indicates that HEV 239 can directly activate B cell more efficiently. These results contribute to a better understanding of the mechanisms involved in the significant high immunogenicity of particulate antigen and may provide knowledge for the rational design and development of future vaccines.

[Priming with an HEV Th epitope can improve the humoral immunogenicity of its native protein].

A dominant H-2d restricted Th epitope P34 was found to be contained in recombinant particulate hepatitis E virus (HEV) vaccine HEV 239. In this paper, the cellular immune response induced in P34 immunized BALB/c mice were studied and the priming effect of P34 was characterized. Groups of BALB/c mice were subcutaneously (s. c.) immunized with P34, splenocytes were then stimulated with P34 and HEV 239 protein, cellular immune response was assayed by IFN-gamma-ELISPOT, flow cytometry and T cell proliferation experiments. Results showed that P34 immunized BALB/c splenocytes responsed to P34 and HEV 239 protein stimulation in IFN-gamma-ELISPOT, flow cytometry and T cell proliferation experiments. After depletion of the CD4+ T cells from the immunized splenocytes by magnetic separation, the response decreased to the background level while almost no influence was observed after CD8 + T cells depletion which showed that the cells responsible for IFN-gamma secretion were mainly CD4+ T cells. Then mice were primed with P34 and boosted with its vector protein, E2, the E2 specific antibody titer were assayed. Results showed that after P34 priming, some of the 10 microg, 20 microg E2 boosted mice could develop anti-E2 antibody 1 week later and all the mice had detectable antibody 3 weeks after boosting. In the control peptide P18 priming group, even after boosting with 20 microg E2, anti-E2 antibody couldn't be detected until the end of this experiment. The results showed that priming with P34 epitope could increase the immunogenicity of its vector protein, E2, in BALB/c mice.