The IgM antibody responses to the core antigen of hepatitis B virus

Little is known about the immunoglobulin class of antibodies to HBcAg. In the present study sera containing anti‐HBc were fractionated by sucrose density‐gradient centrifugation, and all serum fractions were tested against HBcAg by immunoelectro‐osmophoresis. In addition selected fractions were examined by complement fixation test, immune adherence hemagglutination and immune electron microscopy. Anti‐HBc activity in IgG serum fractions was demonstrated by all four techniques used, but HBcAg‐specific IgM was detected only by immunoelectro‐osmophoresis and by immune electron microscopy. In acute hepatitis B, HBcAg‐specific IgM was detected for up to eight weeks after the onset of jaundice. It was also found transiently in two patients who developed chronic hepatitis B without an icteric episode and in one out of thirteen patients with HBsAg‐positive chronic liver disease, but in none of eight healthy HBsAg carriers. The results suggested that HBc Agspecific IgM is formed transiently in response to primary HBV infection but is generally undetectable in established HBsAg carriers.