The first example of anti-Oka was found in a Japanese
woman and was identified by Morel and Hamilton. Since she had never been pregnant, the
antibody most likely was the result of a prior blood transfusion. Two of her three
siblings were also found to be Ok(a-). The Ok(a-) phenotype appears to be limited to the
Japanese as the only other (two) donors who were Ok(a-) were also Japanese.
A monoclonal anti-Oka was produced following immunization
with cells from a teratocarcinoma. This was used to study the biochemical properties of
the Oka antigen. The antigen is expressed on a glycoprotein
having molecular weights ranging from 35,000-68,000. The gene for Oka
is located on chromosome 19p13.2, however, its function is unknown.