Fcγ‐Receptor Activity of Placental Annexin II

We have previously produced a MoAb, B1D6, against a plaeental FcR. The antigen isolated using F(ab')2-fragments of B1D6 exhibits Fc-binding properties with low affinity for IgG. The antigen is a single-chained glycoprotein with a molecular weight of approximately 37 kDa and a pi of about 7.0-8.5. Amino acid sequences from enzymatic digests of the antigen indicated that it is annexin II. Immunoreactivity using anti-annexin antisera and purified placental annexin II have further established the specificity of BID6 to annexin II. The B1D6 epitope appears to be intramembraneous and intracellular on placental syncytiotrophoblasts, monoeytes and other cells investigated.