We detected stable expression of a human embryonic antigen associated with spontaneous abortion (HEAAb) on the cell surface of a tumor promoter (TPA)-treated B-lymphoblastoid cell line (BS-SHY) originating from Bloom syndrome (BS). We used indirect immunofluorescence (IF) and diluted serum from numerous patients who had recurrent spontaneous abortions (RSAs). With the use of the panning procedure, we separated characteristic cells expressing strong HEAAb. The BS-SHY-HEAAb cells separated would be useful for measuring serum antibody (against HEAAb) produced in the immune system of recurrent aborters. Using HEAAb proteins, we conducted Western blot (WB) analysis for the amino acid sequencing (MW, 77 KD). Amino acid sequencing data indicated that HEAAb had 87.5% homology to the immunoglobulin (Ig) VHIII region in the framework, and that differences were due to 2 amino acid alterations; from Gly (G) to Val (V) at the ninth residue and from Gly (G) to asp (D) at the sixteenth residue. No identical mutations were reported in the framework region of IgV(H)III. Even though the exact mechanism of TPA-induced HEAAb expression remains unknown, TPA increases BS SCE from 70 SCE per cell level to approximately 100, thus, it seems plausible that SCE plays some role in the expression of HEAAb, and plays a role in Ig disappearance from BS-SHY-HEAAb cells. Correlation of SCE, mutations causing Ig disappearance and HEAAb expression is discussed.

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