The nucleocapsid of the hepatitis B virus: a remarkable immunogenic structure.

The hepatitis B virus nucleocapsid or core antigen is extremely immunogenic during infection and after immunization. This review summarizes several features of the nucleocapsid which explain this exceptionally high immunogenicity: a unique three-dimensional folding, the presence of a region that interacts with immunoglobulins outside the classical antibody-binding site, the presence of many CD4+ T cell epitopes, and the presence of encapsidated nucleic acids. Because of these features, nucleocapsids efficiently interact and activate antigen presenting cells, especially nai;ve B cells. This leads to the generation of a dominant Th1 immunity phenotype and the secretion of high levels of IgM and IgG anti-nucleocapsid antibodies.