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The HLA DR13 allele has been associated with a self-limited course of hepatitis B virus infection, possibly through the induction of a more vigorous hepatitis B core antigen (HBcAg) and/or hepatitis B e antigen-specific CD4M T cell response. HBcAg-specific CD4M T cell responses were investigated in three HLA DR13-positive subjects with self-limited, acute hepatitis B. HBcAg-specific, short-term T cell lines derived from these three subjects showed a dominant recognition of HBcAg peptides spanning aa 1–20 (P1), 11–30 (P2), 41–60 (P5), 111–131 (P12) and 141–160 (P15). In order to characterize these epitopes in more detail, CD4M T cell clones and cell lines were generated using HBcAg. Surprisingly, 11 of 12 T cell clones examined recognized P15; one recognized P10 (aa 91–111). Of four T cell lines, two recognized P15 and two recognized P5. By peptide mapping, the minimal epitope of P15 was located to residues 147TVVRRRGRSP156