Protective Immunity against Hepatitis C

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A small subset of individuals who are exposed to HCV do not develop anti-HCV antibodies, persistent viraemia or chronic hepatitis despite generating HCV-specific CD4+ and CD8+ T cells. These individuals are believed to develop an immune response which rapidly clears viraemia prior to the induction of an antibody response. Cellular immune responses were evaluated in 23 infants born to HCV positive women. Responses were detected in 1/11 infants born to viraemic mothers, with cytokine production observed in an additional 3/5 infants. Responses were also assessed in multiply transfused subjects with thalassaemia. Responses were detected in 6/13 chronically infected subjects (46%), 4/7 subjects who had cleared infection (71%), and 14/17 seronegative subjects (82%). The third cohort were 41 seronegative injecting drug users, with responses detected in 6 (15%). HCV specific cellular immune responses in seronegative subjects were generally broad in specificity, with a generally Th-1 biased pattern of cytokine production. The findings suggest that responses can be maintained for decades after exposure, and may provide protection against repeated exposures.