Increase in immunoglobulin M antibodies against gut bacteria during acute hepatitis A

The marked increase in the total serum immunoglobulin M (IgM) is a characteristic feature of acute hepatitis A. To study the nature of this IgM, we assayed serial titers of IgM antibodies against various antigens during and after acute hepatitis A. The antibodies against blood group antigen remained unchanged throughout the observation period. Thus, the production or metabolism of IgM was not nonspecifically altered. The IgM antibody against hepatitis A antigen decreased and finally disappeared during convalescence as expected. However, its time course did not correlate quantitatively with the concentration of the total serum IgM. In contrast, IgM antibodies against gut bacteria Bacteroides fragilis and Streptococcus faecalis were considerably elevated in all patients at the onset of the disease, and they normalized similarly to the total IgM during convalescence. IgM antibodies against Escherichia coli were elevated only in some of the patients. The data suggest that the amount of IgM antibodies against gut bacteria contributes significantly to the increase in the total serum IgM in acute hepatitis A.