ABSTRACT: Some normal human sera contain cytotoxic antibodies reacting with an antigen expressed on cultured human fibroblasts and on tissues from fetuses less than three months old. We show that the cytotoxic activity is complement-dependent and mediated by both IgG and IgM antibodies; furthermore, the cytotoxic activity of positive sera of various origins is inhibited by fragments of normal IgG, demonstrating a competition for the same antigen. This antigen is not expressed on freshly prepared fibroblasts and is not related to HLA.
We have tested 96 sera from women at various stages of pregnancy, eight cord blood sera, and 24 control sera for the presence of antifibroblast antibodies (AFA). The results show a progressive and significant increase in the frequency of AFA-positive sera in the second and last trimester of pregnancy. A working hypothesis on the significance of this finding is presented.