Abstract
Patients with autoimmune chronic active hepatitis (AICAH) and certain other chronic liver disorders often have very high titres of haemagglutination ‐inhibition (HI) antibodies to rubella virus. In this study it is shown, using floatation centrifugation, that the high rubella HI reactivity is not caused by nonspecific lipoprotein inhibitors but rather by antibodies specific for the rubella haemagglutinin (E1 glycoprotein). After sucrose density gradient ultracentrifugation of sera the major HI reactivity was recovered in the IgG containing fractions. The IgG antibody fraction was strongly reactive by an indirect enzyme‐linked immunosorbent assay (ELISA). Higher prevalence and titres of rubella antibodies were also demonstrated by the complement fixation (CF) test using a haemagglutinin‐free antigen, and by an indirect haemagglutination (IHA) test (Rubacell) using a cell‐associated antigen which is distinct from the antigens used in the HI and CF tests. This high rubella antibody response is therefore demonstrated using three distinct antigen‐antibody systems. By means of absorption experiments and radioimmunoprecipitation assays the coating antigen used in the IHA test was shown to reside in the E2 glycoprotein. The cause of this enhanced antibody response to rubella virus structural proteins remains elusive. © 1994 Wiley‐Liss, Inc.