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Complete congenital heart block (CCHB) is associated with anti-Ro/SS-A and anti-La/SS-B antibodies. Calreticulin, a calcium-binding, multi-functional protein of the endoplasmic reticulum with C-terminal KDEL-sequence, is not part of the Ro/SS-A ribonucleoprotein complex. In this study anti-calreticulin autoantibody responses in serum samples from 18 infants with CCHB, their mothers and in a control group of 11 anti-Ro/SS-A or anti-La/SS-B positive infants without heart block and their mothers were analysed. Specific enzyme-linked immunosorbent assays were performed. Nine out of 18 sera with CCHB contained IgG anti-calreticulin antibodies. Four sera of those with IgG antibodies also had IgM antibodies. One serum contained anti-calreticulin IgM antibodies only. In the non-CCHB group two sera were positive for IgG and one serum was positive for IgM anti-calreticulin antibodies. Sera of healthy infants were negative both for anti-IgG and anti-IgM calreticulin antibodies. Calreticulin is involved in calcium storage and therefore anti-calreticulin antibodies might influence the development of CCHB. The new finding of IgM autoantibodies and the observed differences in antibody response in infants and mothers support the hypothesis of a fetally mediated and passively acquired autoimmune disease.
Orth et al. (Fri,) studied this question.