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.