| Abstract: | Serum antibodies to human fetal antigens were measured by a radiolabeled anti-immunoglobulin binding assay by using human fetal fibroblasts (Flow cell line No. 1000) as target cells. High titers of IgG antibody to the fetal cells were found in sera of patients with systemic lupus erythematosus (SLE). The antibody reacted with surface membrane antigens shared by various fetal tissues of human and murine origin but not by adult tissues. The reaction of the SLE antibody to the fetal cells was inhibited by heterologous antiserum to the Flow 1000 cells and antiserum to murine embryonic fibroblasts, but not by antiserum to human alpha-fetoprotein or human fibronectin. Absorption of SLE serum with isolated nuclei did not abolish the reaction indicating that these were not anti-nuclear antibodies. The antibody activity was found to reside in the F(ab')2 fragment. The serum titer of the anti-fetal antibody was higher in SLE patients with active disease than those in clinical remission. |
