Studies on the blood of a Co (a-b-) proposita and her family.

The serum of a pregnant woman whose red cells typed as Co(a-b-) contained an alloantibody that, at the time of the infants delivery, was hemolytic in vitro and had a titer of 32,000 by the antiglobulin test. This antibody, which reacted with cells of all Colton-phenotypes except the proposita's own cells, showed very weak reactions with other Co(a-b-) cells and therefore cannot be called anti-Co3. The red cells of the proposita may carry a very weak Co3 antigen. No other persons of the Co(a-b-) phenotype were found in her members, among three of the four generations tested, suggested that an inhibitor gene may be responsible for the unusual Colton phenotypes in this family. The proposita's infant required one exchange transfusion with red cells obtained from the proposita. Red cells from 40,000 donors reacted with the serum of the proposita.