Transforming growth factor (TGF)-β2-related-decidual suppressor factor (DSF) and TJ6 protein are both immunosuppressive molecules present in murine and human pregnancy. Treatment of mice with either anti-TJ6 or anti-TGF-β2 neutralizing antibodies results in increased fetal loss. Western blots of supernatants from pregnant mouse decidua probed with anti-TJ6 (soluble form) showed a doublet at a similar molecular size as when the blot was probed with anti-TGF-β2 antibody. The problem is to determine whether TJ6 and DSF are the same protein. In order to determine if TJ6 and DSF are the same or different proteins, we used affinity column purified TGF-β2-DSF and stained Western blots with anti-TJ6. The TGF-β2-monoclonal antibody affinity column-purified DSF that stained with anti TGF-β2 was not reactive with anti-TJ6 antibody. TJ6 has only a 30% gene sequence homology and a 13% amino acid homology to TGF-β2. TJ6 and TGF-β2-related DSF appear to be different immunosuppressive proteins in decidua.