Hepatic infections. Part I. A serological evaluation of Fab antigens (Fab' and F (ab)2) and antibodies in patients and asymptomatic carriers of hepatitis B virus.

Evidence for the association of Fab (antigen-binding) fragments of IgG and antibodies directed against receptors of these fragments (Fab' and F(ab)2) has been found in patients and asymptomatic carriers of hepatitis B antigen. Fab fragments of IgG are often detected in hepatitis B surface antigen (HBsAg)-positive sera where the intensity of antibody activity to these determinants is significantly reduced. The formation of strong antibodies to Fab fragments is often observed in association with the presence of hepatitis B surface antibodies (HBsAb). Comparative studies show that the appearance of Fab fragments in HBsAg-positive sera is not linked to the presence of hepatitis e antigen. This observation was supported by the finding of autologous Fab fragments of IgG in e antibody-positive sera. It was also established that the amount of Fab fragment in the serum is closely associated with the detection of high HBsAg titres. Preliminary investigations suggest that the Fab fragments of IgG detected in the serum of HBsAg-positive patients represent in vivo-digested HBsAb attached to the surface membrane of virus B particles. Further studies are in progress to determine the relationship of Fab fragments with a variety of other immunological events, especially the role of liver enzymes in the cleavage of intact antibodies.